Chapter 1 Introduction

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1.1 Role of geocycle in the introduction of metals into our environment

Air, water, earth and life are strongly interconnected as shown in Figure 1.1,

which constitute the major segments of the environment- atmosphere, hydrosphere,

geosphere and biosphere. Biogeochemical cycles of matter that involve biological,

chemical and geological processes and phenomena manifests the strong interaction

among living organism and various spheres of the abiotic (nonliving) environment. Water

and air are involved in weathering rocks, producing mineral formations and forming

climate; which have profound effects on the geosphere and interchange matter and energy

with it. Living systems (biosphere) which largely exist on the geosphere in turn have

significant effects on it. However, for better or for worse, the environment in which

human must live have been affected irreversibly by technology and industrial activities.

Metals in the environment may be present in the different states as solid, liquid or gaseous

state or in varying forms as individual elements, organic and inorganic compounds. The

movement of metals between environmental reservoirs may or may not involve changes

of state. Gaseous and particulate metals may be inhaled and solid and liquid (aqueous-

phase) metals may be ingested or absorbed, thereby entering the biosphere [1-3].

Figure 1.1 Interaction of human with the environment

Heavy metals are included within the category of environmental toxins:

“Materials which can harm the natural environment even at low concentration, through

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their inherent toxicity and their tendency to accumulate in the food chain and/or have

particularly low decomposition rates”. The redistribution of many toxic metals into the

environment, caused by the gradual increase in industrial activity, has increased the

possibility of human exposure. Among the various toxic elements, heavy metals like

cadmium, lead, and mercury are especially prevalent in nature due to their high industrial

use. These metals serve no biological function and their presence in tissues reflects

contact of the organism with its environment. They are cumulative poison and are toxic

even at low dose [4,5]. The indication of their importance relative to other potential

hazards is their ranking by the U.S. Agency for Toxic Substances and Disease Registry,

which lists all hazards present in the toxic waste sites according to their prevalence and

severity of their toxicity. The first, second, third and sixth hazards on the list are heavy

metals: lead, mercury, arsenic and cadmium, respectively [6]. The other metal ions that

pose potential dangers to human lives include chromium, copper, zinc, nickel, cobalt, iron

and manganese. Herein, sources and effects of these metal ions are discussed.

Lead

Lead is a highly toxic cumulative poison in humans and animals. Its cumulative

poisoning effects are serious hematological damage, anaemia, kidney malfunctioning,

brain damage etc. In humans, chronic lead poisoning is manifested by abnormalities such

as encephalopathy, nervous irritability, kidney disease, altered heme synthesis and

reproductive functions. Such poisoning is associated with low to intermediate levels of

chronic exposure to lead. The principle risk to children from lead is interference with the

normal development of their brains. A number of studies have found small but significant

neuropsychological impairment in young children due to environmental lead absorbed

either before or after birth. In particular, lead appears to have deleterious effects on

children’s behavior and attentiveness, and possibly also on their IQs.

Environmental contamination of lead is widespread; the main anthropogenic

source of this element is burning of leaded gasoline. Lead is used as a construction

material for equipment used in sulfuric acid manufacture, petrol refining, halogenation,

sulfonation, extraction and condensation. It is used in storage batteries, alloys, solder,

ceramics and plastics. It is also used in the manufacture of pigments, tetraethyl lead and

other lead compounds, in ammunition, and for atomic radiation and x-ray protection.

Lead is used in aircraft manufacture, building construction materials (alloyed with

copper, zinc, magnesium, manganese and silicon), insulated cables and wiring, household

utensils, laboratory equipment, packaging materials, reflectors, paper industry, printing

[7].

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inks, glass industry, water purification and waterproofing in the textile industry. The

primary sources, for low to intermediate levels of chronic exposure to lead, are food,

water and air. About 50% of lead is absorbed with inhalation of dusts, 10–15% absorbed

orally, out of which 90% is distributed to bones [8]. In natural water its typical

concentration lies between 2 and 10 ng mL−1, whereas, the upper limit recommended by

WHO is less than 10 ng mL−1

[9].

Copper

Excess copper interferes with zinc, a mineral needed to make digestive enzymes

[10]. Physical conditions associated with copper imbalance include arthritis, fatigue,

adrenal burnout, insomnia, scoliosis, osteoporosis, heart disease, cancer, migraine

headaches, seizures, fungal and bacterial infections including yeast infection, gum

disease, tooth decay, skin and hair problems and female organ conditions including

uterine fibroids, endometriosis and others. Mental and emotional disorders related to

copper imbalance include depression, mood swings, fears, anxiety, phobias, panic attacks,

violence, autism, schizophrenia, and attention deficit disorder [11]. Copper imbalance in

children is associated with delayed development, attention deficit disorder, anti-social and

hyperactive behavior, autism, learning difficulties and infections such as ear infections.

Copper is primarily used as a metal or an alloy (e.g., brass, bronze, gun metal).

Copper sulfate is used as a fungicide, algaecide and herbicide. Copper particulates are

released into the atmosphere by windblown dust; volcanic eruptions; and anthropogenic

sources, primarily copper smelters and ore processing facilities [12]. Copper particles in

the atmosphere will settle out or be removed by precipitation, but can be resuspended into

the atmosphere in the form of dust. Copper is released into waterways by natural

weathering of soil and rocks, disturbances of soil, or anthropogenic sources (e.g., effluent

from sewage treatment plants) [12]. Another source of copper is drinking water that

remained in copper water pipes, or copper added to your water supply.

Zinc

Zinc is an essential trace element of great importance for humans, plants and

animals. It plays an important role in several biochemical processes and its compounds

have bactericidal activity. Zinc phosphide, which is used as an active ingredient in

rodenticide, reacts with water and acid in the stomach to release phosphine gas which in

turn causes cell toxicity with necrosis of the gastrointestinal tract. Oral zinc increases

faecal excretion of copper and blocks the absorption of ingested minerals. In this case, a

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series of complex zinc-copper relationship and metabolism resulted in the inhibition of

copper absorption and increased faecal loss of copper through saliva, gastric juices and

biliary secretions. Breathing large amounts of zinc (as dust or fumes) can cause a specific

short-term disease called metal fume fever. Inhalation of fumes may result in sweet taste,

throat dryness, cough, weakness, generalized aching, chills, fever, nausea and vomiting.

Zinc chloride fumes have caused injury to mucous membranes and pale gray cyanosis.

Ingestion of soluble salts may cause nausea, vomiting and purging [10,13,14].

Zinc has many commercial uses as coating to prevent rust, in dry cell batteries,

and mixed with other metals to make alloys like brass and bronze. Zinc compounds are

widely used in industry to make paint, rubber, dye, wood preservatives, and ointments

[14]. Also used for galvanizing sheet iron; as ingredient of alloys such as bronze, brass,

Babbitt metal, German silver, and special alloys for die-casting; as a protective coating

for other metals to prevent corrosion, for electrical apparatus, especially dry cell batteries,

household utensils, castings, printing plates, building materials, railroad car linings,

automotive equipment; as reducer (in form of the powder) in the manufacture of indigo

and other vat dyes, for deoxidizing bronze; extracting gold by the cyanide process,

purifying fats for soaps; bleaching bone glue; manufacture of sodium hydrosulfite; as

reagent in analytical chemistry, e.g. in the Marsh and Gutzeit test for arsenic; as a reducer

in the determination of iron. Some zinc is released into the environment by natural

processes, but most comes from activities of people like mining, steel production, coal

burning, and burning of waste.

Cadmium

Cadmium may cause renal injuries and may interfere with the renal regulation of

calcium and phosphate balance. It was seen that exposure to abnormal levels of cadmium

can result in its accumulation in the renal cortex, which causes a series of adverse

subclinical reactions such as hypercalciurium, renal stones and renal tubular dysfunction

besides probable development of carcinogenic activity in organisms [15]. The toxicity of

cadmium may involve its binding to key cellular sulfhydryl groups, its competition with

other metals (zinc and selenium) for inclusion in metalloenzymes, and its competition

with calcium for binding sites on regulatory proteins such as calmodulin. The lack of an

effective elimination pathway is responsible for cadmium’s biologic half-life of 10-30

years. Chronic effects of cadmium exposure are dose-dependent and include anosmia,

yellowing of teeth, emphysema, minor changes in liver function, microcytic hypochromic

anemia unresponsive to iron therapy, renal tubular dysfunction characterized by

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proteinuria and increased excretion of β2-microglobulin and (with prolonged poisoning)

Cadmium is an industrial waste or by-product, which has a great environmental

concern. Cadmium is used in many industrial processes, such as a constituent of easily

fusible alloys, soft solder, electroplating and deoxidizer in nickel plating, engraving

processes, electrodes for vapor lamps, photoelectric cells, and nickel-cadmium storage

batteries [16]. It's wide technological use in fertilizers, mining, pigments, as well as its

delivering from oil and coal burning and residues incineration; bring about an extensive

anthropogenic contamination of soil, air and water.

osteomalacia leading to bone lesions and pseudo fractures [6].

Nickel

Nickel is a moderately toxic element as compared with other transition metals.

However, it is known that inhalation of nickel and its compounds can lead to serious

problems, including respiratory system cancer. Moreover, nickel can cause a skin disorder

known as nickel-eczema. The most common adverse health effect of nickel in humans is

an allergic reaction. People can become sensitive to nickel when things containing it are

in direct contact with the skin, when they eat nickel in food, drink it in water, or breathe

dust containing it. Less frequently, allergic people have asthma attacks following

exposure to nickel. Lung effects, including chronic bronchitis and reduced lung function,

have been observed in workers who breathed large amounts of nickel. Headache,

dizziness, shortness of breath, vomiting, and nausea are the initial symptoms of

overexposure; the delayed effects (10 to 36 h) consist of chest pain, coughing, shortness

of breath, bluish discoloration of the skin, and in severe cases, delirium, convulsions, and

death. [10]. Long-term exposure can cause decreased body weight, heart and liver

damage, and skin irritation. High levels of Ni in the diet may be associated with an

increased risk of thyroid problems, cancer, and heart disease [17,18]. Less frequently,

allergic people have asthma attacks following exposure to nickel. Lung effects, including

chronic bronchitis and reduced lung function, have been observed in workers who

breathed large amounts of nickel.

Major sources of exposure are: tobacco smoke, auto exhaust, fertilizers,

superphosphate, food processing, hydrogenated-fats-oils, industrial waste, stainless steel

cookware, testing of nuclear devices, baking powder, combustion of fuel oil, dental work

and bridges. Humans are exposed to it through breathing of air or smoking of tobacco

containing nickel, eating of food containing nickel, as well as drinking of water

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contaminated with nickel and handling of coins and touching of other metals containing

nickel [19].

Arsenic

Once arsenic is in the body, it binds to hemoglobin, plasma proteins, and

leukocytes and is redistributed to the liver, kidney, lung, spleen, and intestines. Arsenic

produces cellular damage through a variety of mechanisms. Arsenic binds to enzyme

sulfhydryl groups and forms a stable ring, which deactivates the enzyme. The process of

deactivating the enzyme causes widespread endothelial cell damage, vasodilation, and

leakage of plasma. Massive transudation of fluid into the bowel lumen, mucosal vesicle

formation, and tissue sloughing may result in large gastrointestinal fluid losses. Arsenic

binds to dihydrolipoic acid, a pyruvate dehydrogenase cofactor, blocking the conversion

of pyruvate to acetyl coenzyme A and inhibiting gluconeogenesis. Arsenic competes with

phosphates for adenosine triphosphate, forming adenosine diphosphate monoarsine,

causing the loss of high-energy bonds. In some forms, arsenic is caustic, exerting a direct

toxic effect on blood vessels and large organs. Long-term exposure results in nerve

damage and may lead to lung, skin, or liver cancer. Once inhaled, arsine gas combines

with hemoglobin in RBCs, causing severe hemolysis and anemia. Patients develop

hemoglobinuria and hematuria within several hours of exposure. One of the early warning

signs of arsenic poisoning is a "pins and needles" sensation in hands and feet. Long-term

oral exposure to inorganic arsenic can result in skin changes including darkening of the

skin and the appearance of small "corns" or "warts" on the palms, soles, and torso.

Arsenite (should be arsenate) (+5) undergoes biomethylation in the liver to the less toxic

metabolites methylarsenic acid and dimethylarsenic acid; biomethylation can quickly

become saturated, however, and the result is the deposition of increasing doses of

inorganic arsenic in soft tissues [20].

Elevated arsenic (As) levels in the environment are attributable to both natural and

anthropogenic sources, including geothermal discharges, industrial products and wastes,

agricultural pesticides, wood preservatives and mine drainage. It is also used in drugs,

war gases and as a homicidal and suicidal weapon. Other uses of arsenic compounds are

in alloys, manufacturing of arsenic compounds (arsenic oxides) and certain glass. Copper

and lead ores contain small amounts of arsenic. Arsenic is also a major ingredient of

Fowler's solution and continues to be found in some folk remedies [14].

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Mercury

Mercury was recognized as causing neuro-developmental disabilities including

dyslexia, attention deficit hyperactivity disorder, intellectual retardation, and autism [21].

Inhalation of very high concentrations causes acute pulmonary edema and interstitial

pneumonitis, which may be fatal. In non-fatal cases dyspnea and coughing may persist.

Kidney effects may occur at exposure levels lower than those causing central nervous

system effects. Also, mercury vapor may cause “Kawasaki” disease, which seems to be

immunologically mediated and is similar to Pink disease. Mercury intoxication also

causes reproductive effects. Contact dermatitis from mercury amalgam fillings and

mercury sensitivity in dental students has been reported. Repeated or prolonged exposure

to mercury vapor is highly toxic to the central nervous system [20]. Exposures to high

levels of metallic, inorganic, or organic mercury can permanently damage the brain,

kidneys, and developing fetus. Embryo toxicity and teratogenicity of organic mercury

compounds have been reported in many test systems. Exposure to methyl mercury is

worse for young children than for adults, because more of it passes into children’s brains

where it interferes with normal development [22-24].

An organic mercury compound, namely methyl mercury, is produced mainly by

small organisms in water and soil. Metallic mercury is used to produce chlorine gas and

caustic soda and also in thermometers, amalgams (dental fillings), and batteries. Mercury

salts are used in skin-lightening creams and as antiseptic creams and ointments. Mercury

is used in scientific and electrical equipments, in the electrolytic production of chlorine

and sodium hydroxide; and as a catalyst in polyurethane foam production [25]. Inorganic

mercury (metallic mercury and inorganic mercury compounds) enters the air from mining

ore deposits, burning coal and waste, and from manufacturing plants. It enters the water

or soil from natural deposits, disposal of wastes, and the use of mercury-containing

fungicides. Breathing of contaminated air or skin contact during use at workplace (dental,

health services, chemical, and other industries that use mercury) represents occupational

exposures. Inhalation of mercury vapor is the most important route of uptake of elemental

mercury [26].

Chromium

Epidemiological studies have consistently shown that human exposure to Cr (VI)

compounds is associated with a higher incidence of respiratory cancers [27]. Acute toxic

effects occur when one breath very high levels of chromium (VI) in air. It can damage

and irritate nose, lungs, stomach, and intestines. People who are allergic to chromium

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may also have asthma attacks after breathing high levels of either chromium (VI) or (III).

Long term exposures to high or moderate levels of chromium (VI) causes damage to the

nose (bleeding, itching, and sores) and lungs and can increase risk of non-cancer lung

diseases. Ingesting very large amounts of chromium can cause stomach upsets and ulcers,

convulsions, kidney and liver damage, and even death. Skin contact with liquids or solids

containing chromium (VI) may lead to skin ulcers [11,13].

Stainless steel welding, particularly the manual metal arc welding method, may

well be the most common source of occupational exposure to Cr(VI), given the fact that

there are millions of stainless steel welders worldwide. Chromium is used in

manufacturing chrome-steel or chrome-nickel-steel alloys (stainless steel) and other

alloys, bricks in furnaces, and dyes and pigments, for greatly increasing resistance and

durability of metals and chrome plating, leather tanning, and wood preserving. Handling

or breathing sawdust from chromium treated wood, manufacturing, disposal of products

or chemicals containing chromium, or fossil fuel burning release chromium to the air,

soil, and underground water [28].

Manganese

Exposure to atmospheric Mn at high concentration is a risk factor in humans that

can manifest as neuronal degeneration resembling Parkinson's disease (PD). Although the

underlying mechanism of Mn and dopamine (DA) interaction-induced cell death remains

unclear, however, Mn exposure alone to mesencephalic cells for 24h induced minimal

apoptotic cell death [29]. Increased manganese intake impairs the activity of copper

metallo-enzymes. Excess manganese interferes with the absorption of dietary iron. Long-

term exposure to excess levels may result in iron-deficiency anemia. High manganese

levels indicate problems with calcium and/or iron metabolism [11,13]. Symptoms of

toxicity mimic those of Parkinson's disease (tremors, stiff muscles) and excessive

manganese intake can cause hypertension in patients older than 40 [30]. Symptoms of

increased manganese levels include psychiatric illnesses, mental confusion, impaired

memory, loss of appetite, mask-like facial expression and monotonous voice, spastic gait

and neurological problems. Manganese toxicity can cause kidney failure, hallucinations,

as well as diseases of the central nervous system.

Uses of Mn include: (i) iron and steel production; (ii) manufacture of dry cell

batteries; (iii) production of potassium permanganate and other Mn chemicals; (iv)

oxidant in the production of hydroquinone; (v) manufacture of glass; (vi) textile

bleaching; (vii) oxidizing agent for electrode coating in welding rods; (viii) matches and

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fireworks; and (ix) tanning of leather [31]. Organic compounds of Mn are present in the

fuel additive, methylcyclopentadienyl manganese tricarbonyl (MMT), fungicides (e.g.,

maneb and mancozeb), and in contrast agents used in magnetic resonance imaging. The

primary anthropogenic sources of Mn in ambient air include emission of Mn from

industrial sources such as ferroalloy production plants, iron and steel foundries, power

plants, and coke ovens and re-entrainment of soils containing Mn [32]. Well water rich in

manganese can be the cause of excessive manganese intake and can increase bacterial

growth in water. Manganese poisoning has been found among workers in the battery

manufacturing industry.

Cobalt

Cobalt metal particles, when inhaled in association with other agents such as

metallic carbides (hard metals) or diamond dust, may produce an interstitial lung disease

termed "hard metal disease" or "cobalt lung". Acute toxicity of cobalt may be observed as

effects on the lungs, including asthma, pneumonia and wheezing, that have been found in

workers who breathed high levels of cobalt in the air. The International Agency for

Research on Cancer (IARC, USA) has determined that cobalt is a possible carcinogen to

humans. Studies in animals have shown that cobalt causes cancer when placed directly

into the muscle or under the skin [11,13,33].

Vast applications of cobalt in various arrays of products and processes such as its

use in alloys, batteries, catalysts, pigments and coloring, make this element to be

considered as an important metal in various industries [34]. Cobalt enters the environment

from natural sources and from the burning of coal and oil. Workers may be exposed to

cobalt in industries that process it or make products containing cobalt [35].

Iron

Excessive iron leads to tissue damage as a result of formation of free radicals [36].

Long term over consumption of iron may cause hemosiderosis, a condition characterized

by large deposits of the iron storage protein hemosiderin in the liver and other tissues.

Iron overload is most often diagnosed when tissue damage occurs, especially in iron-

storing organs, such as the liver. Infections are likely to develop because bacteria thrive

on iron rich blood. Ironically, some of the signs of iron overload are analogous to those of

iron deficiency: fatigue, headache, irritability, and lowered work performance. Other

common symptoms of iron overload include enlarged liver, skin pigmentation, lethargy,

joint diseases, loss of body hair, amenorrhea, and impotence. Untreated hemochromatosis

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aggravates the risks of diabetes, liver cancer, heart disease and arthritis. In cases of iron

overload the natural storage and transport proteins are overwhelmed and the iron spills

over into other tissues and organs, such as the muscle, spleen and liver [37], proving to be

toxic [38].

Iron is included in the quality control of industrial and commercial products such

as petroleum, alloys, foods, beverages etc [20]. Occasionally, iron pipes may also be a

source of iron in water. Water percolating through soil and rock can dissolve minerals

containing iron and manganese and hold them in solution.

1.2 Significance and characteristics of preconcentration

Determination of toxic metal ions in environmental samples, wastewater, various

natural water bodies and biological fluids is necessary for environment monitoring,

assessment of occupational and environmental exposure to toxic metals and its impact on

the ecosystem.

The low concentrations of the metal ions and the strong interference of matrices

present in association with it, in real samples, poses difficulty in its direct determination

despite the availability of sophisticated instrumental methods, with excellent sensitivity

and multielemental analysis capability [39-46]. A radical way to eliminate matrix effects

is a preliminary separation of macro components by a relative, or absolute,

preconcentration of trace metals.

Preconcentration can be of two types: absolute and relative preconcentration.

Absolute prenconcentration involves the transfer of trace elements from a large mass of

sample into a small mass, e.g. by evaporation or by solvent extraction into a small volume

of an organic phase.

Relative preconcentration involves at least partial separation of the components when

their concentrations differ very much. Its main aim is often to exchange the matrix for a

suitable collector (generally of smaller mass) to prevent its interference in the

determination. In some cases, it is difficult to define a boundary between absolute and

relative preconcentration. Relative preconcentration increases the mass ratio of trace

elements to main components (the solvent is not considered as a major component in this

case).

Depending on the purpose, trace elements can be concentrated selectively or in

groups and either separation of the matrix or separation of the trace components can be

used. Removal of the matrix is reasonable if used in combination with multi element

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determination techniques, e.g. spectrochemical analysis, but only if the matrix is of

simple composition. Matrix removal is used especially in analysis of high-purity metals.

If the matrix contains several elements forming complex compounds (geological and

biological materials), it is better to separate the trace elements. Sometimes, there is no

need to remove the matrix completely; the process is then called "enrichment". However,

it is usually more profitable to change to another matrix which better meets the demands

of the subsequent determination, simplifies a calibration, etc. Several such collectors are

suitable for determinations by different techniques. For instance, carbon powder can be

analyzed by a spectrographic method or by flameless atomic-absorption

spectrophotometry [47].

Some quantitative characteristic features used for description of prenconcentration

are listed in Table 1.1

Table 1.1 Characteristic features of preconcentration Recovery (R) R = QT/Q°T, where QT and Q°T are respectively the

quantities of trace element in the concentrate and in the

sample. It is usually expressed as a percentage.

Concentration coefficient (K)

K = (QT/QM) / (Q°T/Q°M), where Q°M and QM are

respectively the amounts of matrix before and after

preconcentration. If R = 100% then K = Q°M/QM

Separation coefficient (S)

.

S = (QM/QT) / (Q°M/Q°T

Preconcentration factor

) = 1/K

Maximum volume of sample / minimum eluent volume

that gives quantitative recovery of analyte

Preconcentration limit (µg L-1 Minimum concentration up to which preconcentration

(maximum volume) is feasible.

)

Of the analytical techniques for preconcentration and separation, SPE has been

preferred over conventional solvent extraction and coprecipitation. The markedly lower

quantity of reagents required, the fact that solid phase can be repeatedly used, higher

concentration factors, and simplicity in handling and transfer are frequently quoted as

advantages [48-51]. Sorption and ion exchange have been studied for different analytical

applications [52–60] using various support materials. Many different methods are used

for analytical preconcentration [61]. They can be classified according to the nature of the

separations (chemical and physical methods) used and the number and nature of the

phases involved in the separation process.

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Solvent extraction [62-64]

Co-precipitation [65-67]

Evaporation methods [68]

Electrochemical Techniques [69-70]

Crystallization [71]

Flotation [72]

Membrane filtration [73]

Cloud point extraction [74]

Solid-phase extraction (SPE) [75,76]

1.3 Solid-phase extraction (SPE ) as a preconcentration method

It is a separation process that is used to remove solid or semi-solid compounds

from a mixture of impurities based on their physical and chemical properties. Analytical

laboratories use solid phase extraction to concentrate and purify samples for analysis. The

separation ability of solid phase extraction is based on the preferential affinity of desired

or undesired solutes in a liquid (mobile phase) for a solid (stationary phase) through

which the sample is passed. Impurities in the sample are either washed away while the

analyte of interest is retained on the stationary phase, or vice-versa. Analytes that are

retained on the stationary phase can then be eluted from the solid phase extraction

cartridge with the appropriate solvent. The preconcentration methods utilizing solid

sorbents are considered to be superior than the liquid-liquid extraction in terms of

simplicity, rapidity, and the ability to obtain a high enrichment factor. Particularly, solid

phase extraction has been demonstrated in various procedures to be a very effective

preconcentration technique in combination with atomic absorption spectrometry. The

main advantage of this technique is the possibility of using a relatively simple detection

system with flame atomization instead of a flameless technique, which require more

expensive equipment and are usually much more sensitive to interferences from

macrocomponents of various natural matrices [39].

1.3.1 History and development of SPE

The history of using solid phases to isolate drugs from biological samples dates

back to 1923 when permutite was used [77] and then subsequently silicic acid [78] for

extracting adrenaline. In the 1950s, alumina columns were used [79] for extracting

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adrenaline and noradrenaline from blood samples. Then successful extraction of catechol

bases, adrenaline and histamine from crude extracts of glands, using Amberlite IRC-50

[80] was performed. Later a method was developed to extract catechol amines from

tissues using cation exchange resin Dowex 50 [81]. By the mid 1960s more complex

samples were being tried. A method using cation exchange paper chromatography [82],

which was qualitative in nature, was developed to detect a number of narcotics,

tranquilizers, amphetamines and barbiturates from urine samples but the method was

more. In the 1970s, the stress was to develop techniques which were more sensitive.

Amberlite XAD-2 resin columns were used to quantify narcotic analgesics from urine and

could determine as low as 0.6 mg mL of urine [83]. It is noted that, in most of the above

cases, the principle of ion exchange was used to separate drugs from biological samples.

Subsequently, adsorption phenomenon was tried on charcoal to concentrate a number of

drugs (barbiturate, glutathimide, ethchlorvynol, amphetamine, phenothiazine, quinine,

morphine, cocaine and its metabolites) from urine and achieved an average detection limit

of 1 mg mL-1

Solid-phase extraction is now emerging as a very important sample preparation

technique. It is preferred over other traditional procedures, such as liquid-liquid extraction

(LLE), mainly because it is more efficient and much less time-consuming.

of urine [84]. By the late 1970s, HPLC technology had made rapid progress

and one of the major developments was the use of silica and bonded silica as the

stationary phase. Waters Associates and Analytichem International were among the first

to develop the concept of using sorbents, similar to those used in HPLC, packed in

miniature columns, to isolate drugs and chemicals from other interfering impurities of test

samples. Specifically, small disposable cartridges containing silica, bonded silica and

other phases were developed for commercial use and these were called SPE columns. Cl8

SepPak@ columns (Waters Associates) were evaluated for the extraction of tricyclic

antidepressants from biological samples [85].

1.3.2 Basic principles

The principle of SPE is similar to that of liquid-liquid extraction (LLE), involving

a partitioning of solutes between two phases. However, instead of two immiscible liquid

phases, as in LLE, SPE involves partitioning between a liquid (sample matrix) and a solid

(sorbent) phase. This sample treatment technique enables the concentration and

purification of analytes from solution by sorption on a solid sorbent.

The basic approach involves passing the liquid sample through a column, a

cartridge, a tube or a disk containing an adsorbent that retains the analytes. After the

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entire sample has been passed through the sorbent, retained analytes are subsequently

recovered upon elution with an appropriate solvent. The first experimental applications of

SPE started fifty years ago [86,87].

1.3.3 Technique

An SPE method always consists of three to four successive steps, as illustrated in

Figure 1.2.

Figure 1.2 SPE operation steps.

STEP 1: The solid sorbent should be conditioned using an appropriate solvent, followed

by the same solvent as the sample solvent.

Significance:

This step is crucial, as it enables the wetting of the packing material and the

solvation of the functional groups.

In addition, it removes possible impurities initially contained in the sorbent or the

packaging.

Also, this step removes the air present in the column and fills the void volume with

solvent.

The nature of the conditioning solvent depends on the nature of the solid sorbent.

Care must be taken not to allow the solid sorbent to dry between the conditioning

and the sample treatment steps, otherwise the analytes will not be efficiently

retained and poor recoveries will be obtained.

If the sorbent dries for more than several minutes, it must be reconditioned.

STEP 2: The second step is the percolation of the sample through the solid sorbent.

Depending on the system used, volumes can range from 1 mL to 1000 mL. The

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sample may be applied to the column by gravity, pumping, aspirated by vacuum

or by an automated system.

Significance:

The sample flow-rate through the sorbent should be low enough to enable efficient

retention of the analytes, and high enough to avoid excessive duration.

During this step, the analytes are concentrated on the sorbent.

Even though matrix components may also be retained by the solid sorbent, some of

them pass through, thus enabling some purification (matrix separation) of the

sample.

STEP 3: The third step (which is optional) may be the washing of the solid sorbent with

an appropriate solvent, having low elution strength, to eliminate matrix

components that have been retained by the solid sorbent, without displacing the

analytes.

Significance:

A drying step may also be advisable, especially for aqueous matrices, to remove

traces of water from the solid sorbent.

This will eliminate the presence of water in the final extract, which, in some cases,

may hinder the subsequent concentration of the extract and or the analysis.

STEP 4: The final step consists in the elution of the analytes of interest by an appropriate

solvent, without removing retained matrix components.

Significance:

The solvent volume should be adjusted so that quantitative recovery of the analyte is

achieved with subsequent low dilution.

In addition, the flow-rate should be correctly adjusted to ensure efficient elution.

It is often recommended that the solvent volume be fractionated into two aliquots,

and before the elution to let the solvent soak the solid sorbent.

1.3.4 Mechanism of retention

Adsorption of trace elements on the solid sorbent is required for preconcentration

(Figure 1.3). The mechanism of retention depends on the nature of the sorbent, and may

include simple adsorption, chelation or ion-exchange. Active functional groups of the

16

ligand moiety are responsible for the selective chelation with the metal ions whereas

macro porous polymeric support offers large surface area.

Adsorption

Trace elements are usually adsorbed on solid phases through van der Waals forces

or hydrophobic interaction. Hydrophobic interaction occurs when the solid sorbent is

highly non-polar (reversed phase). The most common sorbent of this type is octadecyl-

bonded silica (C18-silica). More recently, reversed polymeric phases have appeared,

especially the styrene-divinylbenzene copolymer that provides additional pi-pi interaction

when p-electrons are present in the analyte [88]. Elution is usually performed with

organic solvents, such as methanol or acetonitrile. Such interactions are usually preferred

with online systems, as they are not too strong and thus they can be rapidly disrupted.

However, because most trace element species are ionic, they will not be retained by such

sorbents.

Chelation

Several functional group atoms are capable of chelating trace elements. The

atoms most frequently used are nitrogen (e.g. N present in amines, azo groups, amides

and nitriles), oxygen (e.g. O present in carboxylic, hydroxyl, phenolic, ether, carbonyl,

phosphoryl groups) and sulfur (e.g. S present in thiols, thiocarbamates and thioethers).

The nature of the functional group will give an idea of the selectivity of the ligand

towards trace elements. In practice, inorganic cations may be divided into 3 groups:–

1. Group I-‘hard’ cations: these preferentially react via electrostatic interactions (due to

a gain in entropy caused by changes in orientation of hydration water molecules); this

group includes alkaline and alkaline-earth metals (Ca2+, Mg2+, Na2+

2. Group II-‘borderline’ cations: these have an intermediate character; this group

contains Fe

) that form rather

weak outer-sphere complexes with only hard oxygen ligands.

2+, Co2+, Ni2+, Cu2+, Zn2+, Pb2+, Mn2+

3. Group III-‘soft’ cations: these tend to form covalent bonds. Hence, Cd

. They possess affinity for both hard

and soft ligands. 2+and Hg2+

Chelating agents may be directly added to the sample for chelating trace elements,

the chelates being further retained on an appropriate sorbent. An alternative is to

possess strong affinity for intermediate (N) and soft (S) ligands. For soft metals, the

following order of donor atom affinity is observed: O<N<S.

17

introduce the functional chelating group into the sorbent. For that purpose, three different

means are available:

1. The synthesis of new sorbents containing such groups (new sorbents);

2. The chemical bonding of such groups on existing sorbents (functionalized sorbents);

and

3. The physical binding of the groups on the sorbent by impregnating the solid matrix

with a solution containing the chelating ligand (impregnated, coated or loaded

sorbents).

The latter remains the most simple to be used in practice. Its main drawback is the

possible flush of the chelating agent out of the solid sorbent during sample percolation or

elution that reduces the lifetime of the impregnated sorbent. Different ligands

immobilized on a variety of solid matrices have been successfully used for the

preconcentration, separation and determination of trace metal ions. Chelating agents with

a hydrophobic group are retained on hydrophobic sorbents (such as C18-silica). Similarly,

ion-exchange resins are treated with chelating agents containing an ion exchange group,

such as a sulfonic acid derivative of dithizone (i.e. diphenylthiocarbazone) (DzS), 5-sulfo-

8-quinolinol, 5-sulfosalicylic acid, thiosalicylic acid, chromotropic acid, or

carboxyphenylporphyrin (TCPP) [89-92].

Binding of metal ions to the chelate functionality is dependent on several factors:

nature, charge and size of the metal ion;

nature of the donor atoms present in the ligand;

buffering conditions which favor certain metal extraction and binding to active

donor or groups; and

nature of the solid support (e.g. degree of cross-linkage for a polymer).

In some cases, the behavior of immobilized chelating sorbents towards metal

preconcentration may be predicted using the known values of the formation constants of

the metals with the investigated chelating agent [93]. However, the presence of the solid

sorbent may also have an effect and lead to the formation of a complex with a different

stoichiometry than the one observed in a homogeneous reaction [94, 95]. In fact, several

characteristics of the sorbent should be taken into account, namely the number of active

groups available in the resin phase [93-96], the length of the spacer arm between the resin

and the bound ligand [97], and the pore dimensions of the resin [98].

18

Ion-pairing

When a non-polar sorbent is to be used, an ion-pair reagent (IP) can be added to

the sorbent [99]. Such reagents contain a nonpolar portion (such as a long aliphatic

hydrocarbonated chain) and a polar portion (such as an acid or a base). Typical ion-pair

reagents are quaternary ammonium salts and sodium dodecylsulfate (SDS) [100,101]. The

non-polar portion interacts with the reversed-phase non-polar sorbent, while the polar

portion forms an ion-pair with the ionic species present in the matrix (that could be either

free metallic species in solution or complexes).

Ion exchange

Ion-exchange sorbents usually contain cationic or anionic functional groups that

can exchange the associated counter-ion. Strong and weak sites refer to the fact that

strong sites are always present as ion-exchange sites at any pH, while weak sites are only

ion-exchange sites at pH values greater or less than the pKa. Strong sites are sulfonic acid

groups (cation-exchange) and quaternary amines (anion-exchange), while weak sites

consist of carboxylic acid groups (cation-exchange) or primary, secondary and tertiary

amines (anion-exchange). These groups can be chemically bound to silica gel or polymers

(usually a styrene-divinylbenzene copolymer), the latter allowing a wider pH range. An

ion-exchanger may be characterized by its capacity, resulting from the effective number

of functional active groups per unit of mass of the material. The theoretical value depends

upon the nature of the material and the form of the resin. However, in the column

operation mode, the operational capacity is usually lower than the theoretical one, as it

depends on several experimental factors, such as flow-rate, temperature, particle size and

concentration of the feed solution. As a matter of fact, retention on ion-exchangers

depends on the distribution ratio of the ion on the resin, the stability constants of the

complexes in solution, the exchange kinetics and the presence of other competing ions.

Even though ion-exchangers recover hydrated ions, charged complexes and ions

complexed by labile ligands, they are of limited use in practice for preconcentration of

trace elements due to their lack of selectivity and their retention of major ions [102]. Yet,

for some particular applications they may be a valuable tool. Hence, iron speciation is

possible through selective retention of the negative Fe(III)-ferron complex on an anion-

exchanger [103]. Selenium speciation is also feasible by selectively eluting Se(IV) and

Se(VI) retained on a anion-exchanger [104].

19

Figure 1.3 Interactions occurring at the surface of the solid sorbent

F-functional group; TE-trace element; MS-matrix solvent; MI-matrix ions; ES-elution

solvent.

1.3.5 Mechanism of elution of trace elements from the sorbent

Similar kinds of interactions (as mentioned in the previous section) usually occur

during the elution step. The type of solvent must be correctly chosen to ensure stronger

affinity of the trace element to the solvent, to ensure disruption of its interaction with the

sorbent (Figure 1.3). Thus, if retention on the sorbent is due to chelation, the solvent

could contain a chelating reagent that rapidly forms a stronger complex with the trace

metal. Elution may also be achieved using an acid that will disrupt the chelate and

displace the free trace element. Similarly, if retention is due to ion exchange, its pH

dependence enables the use of eluents with different pH to be used, such as acids. Of

prime importance is to selectively elute only the target species. So, if they are more

strongly retained on the sorbent than the interfering compounds, a washing step with a

solvent of moderate elution strength is highly advisable before elution of the target

species with the appropriate solvent.

1.3.6 Selection of Solid Sorbents

The nature and properties of the sorbent are of prime importance for effective

retention of metallic species. In practice, the main requirements for a solid sorbent are:

20

The possibility to extract a large number of trace elements over a wide pH range

(along with selectivity towards major ions);

Kinetically faster quantitative sorption and elution;

A high capacity;

Regenerability; and

Accessibility

Solid sorbents may be reversed-phase sorbents or normal-phase sorbents.

Reversed-phase sorbents usually refer to the packing materials that are more

hydrophobic than the sample, which are frequently used with aqueous samples. When

hydrophobic supports are used, retention of ionic metal species will require the formation

of hydrophobic complexes. This can be achieved through addition of the proper reagent to

the sample or through immobilization of the reagent on the hydrophobic solid sorbent.

Normal-phase sorbents refer to materials more polar than the sample and they are

used when the sample is an organic solvent containing the target compounds.

Nascent polymeric resins as sorbent

Nascent styrene–DVB resins such as Amberlite XAD-1180 [105,106], XAD-4

[107], and XAD-16 [108-112] are used directly for enrichment of inorganic species as

their halide or thiocyanate complex. The type and quantity of sorbent, hydrophobicity,

ionizability of the analytes, sample volume and pH interactively determine the

breakthrough volume. Using a styrene–divinylbenzene sorbent, the primary interaction

mechanism is via Vander Waals forces; therefore, the more hydrophobic the compound

the larger the breakthrough volume will be and the larger the sample size from which

quantitative recovery can be expected. This observation can be generalized to other

sorbents by stating that regardless of the primary interaction mechanism between the

analyte and the sorbent, it holds true that the stronger the interaction, the larger the

breakthrough volume will be.

Modification of nascent polymeric resins

. Macroporous hydrophobic resins of the Amberlite XAD series

[polystyrenedivinylbenzene (PS-DVB) resins] are good supports for developing chelating

matrices. Amberlite XAD resins, as the copolymer backbone for the immobilization of

chelating ligands, have some physical superiority, such as porosity, uniform pore size

distribution, high surface area and chemical stability towards acids, bases, and oxidizing

agents, as compared to other resins. In addition to the hydrophobic interaction that also

21

occurs with C18-silica, such sorbents also allow π-π interactions. Due to the hydrophobic

character of PS-DVB, retention of trace elements on such sorbents requires the addition

of a ligand to the sample. The use of surface-modified PS–DVB copolymers with

different polar substituent overcomes the following disadvantages suffered by standard

silica-based material used for SPE:

lack of pH stability under acidic or basic conditions,

low breakthrough for polar analytes,

they are not wettable by water alone and always need a conditioning step with a

wetting solvent, such as methanol.

However, in practice, the resins prepared by impregnation of the ligand are difficult

to reuse, due to partial leaching of the ligand (thus resulting in poor repeatability). To

overcome this problem, the resin may be chemically functionalized. Chemical

modification of PS–DVB copolymers have been carried out by immobilizing varying

substituents through different bridging groups.

Amberlite XAD-2

Surface modification: Amberlite XAD-2 resin modified by surface adsorption with oxime

[113,114] 1-(2-thiazolylazo)-2-naphthol [113,115], pyrocatechol violet [113], 4-(2-

pyridylazo) resorcinol [114], eriochrome blue black R [114], ammonium pyrollidine

dithiocarbamate (APDC) [116], tropolone [117], 1-(2-pyridylazo)- 2-naphthol (PAN)

[118], 2-(2-thiazolylazo)-p-cresol [119], calmagite [120,121], and organophosphinic acid

[122] were used as solid phase extractant sorbents in off-line or online column

preconcentration modes.

Chemical modification: Singh et al. chemically immobilized AmberliteXAD-2 with

alizarin Red S [123], tiron [124], catechol [125], thiosalicylic acid [126], o-aminophenol

[127], chromotropic acid [128], catechol violet [129], salicylic acid [130], and pyrogallol

[125] via azo (-N=N-) spacer. A similar synthetic scheme was employed by Jain et al.

[131, 132] to chemically immobilize o-vanilline thiosemicarbazone on to Amberlite

XAD-2 resin. Dogutan et al. [133] synthesized palmitoyol-8-hydroxyquinoline

functionalized Amberlite XAD-2 by a modified procedure described by Suebert et al.

[134] through chloromethylation. In 1992, Trojanowicz group [135] chemically

immobilized Eriochrome blue black R onto Amberlite XAD-2. Yuan and Shuttler [136]

immobilized quinoline-8-ol onto Amberlite XAD-2 and controlled pore glass, and

22

reported higher enrichment factors with the former as it gave higher flow rates during

quantitation of aluminum by FIA-ETAAS.

Amberlite XAD-4

Surface modification: Surface adsorption of Amberlite XAD-4 resin beads with oxine

[137-140], APDC [137, 138], 2[2-(5-chloropyridyl)azo]- 5-dimethyl amino phenol (5-

ClDMPAP) [139,140], butane–2,3-dionebis(N-pyridinoacetylhydrazone)[141], 2-(5-

bromo-2-pyridylazo)-5-diethyl aminophenol (5-Br PADAP) [142-144], 5-phenyl azo-8-

quinolinol [145], 1-nitroso-2-napthol [146], and N-benzoylphenylhydroxylamine [147]

were used as solid-phase extractants for the trace determination of inorganics using a

variety of detection techniques which include spectral and X-ray techniques.

Chemical modification: Azotization was used for immobilzation of o-aminobenzoic acid

onto Amberlite XAD-4 resin by Cekic et al. [148]. Jain et al. [149] employed similar

synthetic scheme for functionalizing Amberlite XAD-4 with o-vanilline-semicarbazone.

Amberlite XAD-4 was functionalized with N-hydroxy ethyl ethylene diamine via

acylation by Hirata et al. [150] as per the synthesis procedure described by Dev and Rao

[151]. Acid chloride was grafted onto Amberlite XAD-4 [152], Yakin and Apak [153]

immobilized maleic acid by electrophilic substitution of the Amberlite XAD-4 resin with

maleic anhydride by a Friedel-Crafts reaction. Quinoline-8-ol functionalized Amberlite

XAD-4 resin was synthesized by Gladis and Rao [154] through acetylation.

Amberlite XAD-16

Surface modification: Traces of inorganics were enriched on Amberlite XAD-16 resin

beads after surface adsorption with a variety of chelates, namely PAN [155], NaDDTC

[156,157], 4-(2-thiazoylazo) resorcinol [158,159], N,N-dibutyl-N-benzoylthiourea

(DBBT) [160], and di-(2-ethylhexyl phosphoric acid (D2EHPA) [161].

Chemical modification: Azotization was employed to functionalize (bis-2,3,4-trihydroxy

benzyl)ethylene diamine(BTBED) [162], 2-{[1-(3,4-Dihydroxyphenyl)methylidene]

amino}-benzoic acid (DMABA) [163], 4-{[(2-Hydroxyphenyl)imino]methyl}-1,2-

benzenediol (HIMB) [164] and Nitrosonaphthol [165] on to Amberlite XAD-16. D.

Prabhakaran et. al. immobilized 1,3-dimethyl-3-aminopropan-1-ol onto Amberlite XAD-

16 via simple condensation mechanism [166].

23

Apart from this a number of different solid sorbents have been investigated for the

preconcentration of trace metals from an aqueous solution. They include:

Silica gel (Inorganic based sorbents) [167-172]

C-bonded silica gel (Inorganic based sorbents) [173-178]

Other inorganic oxides (Inorganic based sorbents)[179-182]

Divinylbenzene-vinylpyrrolidone copolymers (polymeric organic sorbents)[183-

184]

Polyacrylate polymers (polymeric organic sorbents)[185-187]

Polyurethane polymers (polymeric organic sorbents)[188-192]

Polyethylene polymers (polymeric organic sorbents)[193]

Polytetrafluoroethylene polymers (polymeric organic sorbents)[194-196]

Polyamide polymers (polymeric organic sorbents)[197]

Iminodiacetate-type chelating resins (polymeric organic sorbents)[198-201]

Propylenediaminetetraacetate-type chelating resins (polymeric organic

sorbents)[202]

Polyacrylonitrile based resins (polymeric organic sorbents)[203-206]

Ring-opening metathesis polymerization based polymers (polymeric organic

sorbents)[207,208]

Carbon sorbents (non-polymeric organic sorbents)[209-215]

Cellulose (non-polymeric organic sorbents)[216-218]

Naphthalene based sorbents (non-polymeric organic sorbents)[219-226]

Molecularly Imprinted Polymers (MIP) [227,228]

1.3.7 Advantages of SPE

Reduced detection limit

This step is used if the detection limit of the analytical technique is higher than

the concentration of trace elements in the sample. Concentration often involves separation

of the matrix or the bulk of it, and sometimes a number of interfering minor constituents

as well. In a prepared concentrate, the relative concentration of trace elements is usually

higher than in the initial sample. Moreover, the possibility of increasing the amount of

sample analyzed means that the absolute amounts of elements to be determined can also

be increased. As a result, it is possible to reduce the detection limit of trace elements

(sometimes very significantly; by a factor of 100 or 1000). This is the main but not the

only reason for the widespread use of preconcentration [229].

24

Preparation of a representative sample

Preconcentration is almost essential if trace elements are non-homogeneously

distributed in the material. In this case, a representative sample must be quite large; it is

difficult to analyze it directly, especially if the method of determination needs a small

sample as, for instance, spark-source mass-spectrometry or spectrochemical analysis. In

many other cases, preconcentration with preliminary dissolution and production of a

small volume of concentrate facilitates the preparation of a representative sample.

Samples can be homogenized during other operations also. SPE enjoys superiority over

solvent extraction as it is free from difficult phase separation, which is caused by the

mutual solubility between water and organic solvent layers [230].

Facilitates calibration

Concentration facilitates calibration, especially if there is a lack of standard

reference materials. It makes it possible to obtain concentrates with identical matrices in

analysis of quite different materials, for example, concentrates on carbon powder in

spectrochemical analysis. Reference samples are prepared as concentrates of the same

type. There is then no necessity to have standard reference materials for all substances

analyzed. Preconcentration with exhaustive removal of the matrix is desirable in the

analysis of toxic, radioactive or, if the matrix can be recovered, very expensive materials.

Moreover, it is convenient to add elements as internal standards, if necessary, during

decomposition of the sample and concentration. Sometimes, preconcentration allows an

increase in the number of trace elements which can be determined by a selected technique

or makes it possible for the determination technique to be used at all. These advantages of

preconcentration make it an important part of trace analysis. In spite of the progress in

sensitive instrumental methods of direct analysis, the significance of concentration does

not diminish. On the contrary, its possibilities increase, particularly because of new

combinations with methods of determination [39,231].

Other attractive features

This technique is attractive as it reduces consumption of and exposure to solvents,

their disposal costs and extraction time [232]. It also allows the achievement of high

recoveries, along with possible elevated enrichment factors. However, different results

between synthetic and real samples may be observed [233]; recoveries should be

estimated in both cases as far as possible. Its application for preconcentration of trace

metals from different samples is also very convenient due to sorption of target species on

25

the solid surface in a more stable chemical form than in solution. Use of carcinogenic

organic solvents is avoided and thus the technique is ecofriendly to nature. Finally, SPE

affords a broader range of applications due to the large choice of solid sorbents.

High preconcentration factor

The use of SPE enables the simultaneous preconcentration of trace elements,

removal of interferences, and reduces the usage of organic solvents that are often toxic

and may cause contamination. Upon elution of the retained compounds by a volume

smaller than the sample volume, concentration of the extract can be easily achieved.

Hence, concentration factors of up to 1000 may be attained [229].

Preservation and storage of the species

SPE allows on-site pre-treatment, followed by simple storage and transportation

of the pre-treated samples with stability of the retained metallic species for several days

[234,235]. This point is crucial for the determination of trace elements, as the transport of

the sample to the laboratory and its storage until analysis may induce problems, especially

changes in the speciation. In addition, the space occupied by the solid sorbents is minimal

and avoids storage of bulky containers and the manpower required to handle them.

Selective extraction

SPE offers the opportunity of selectively extracting and preconcentrating only the

trace elements of interest, thereby avoiding the presence of major ions. This is crucial in

some cases, such as with spectrophotometric detection, since the determination of heavy

metals in surface waters may necessitate the removal of non-toxic metals, such as Fe or

Zn, when they occur at high concentrations [236]. It may also be possible to selectively

retain some particular species of a metal, thereby enabling speciation. For example, salen

I modified C18-silica is quite selective towards Cu(II) [237], while chemical binding of

formylsalicylic acid on amino-silica gel affords selectivity towards Fe(III) [238]. This

high selectivity may also be used to remove substances present in the sample that may

hinder metal determination, such as lipid substances in the case of biological samples

[239]. The chelating resin method is an economical method since it uses only a small

amount of ligand and extraction solvent and this also increases the sensitivity of the

system.

26

Automation and possible on-line coupling to analysis techniques

SPE can be easily automated, and several commercially available systems have

been recently reviewed [239]. In addition, SPE can be coupled online to analysis

techniques. On-line procedures avoid sample manipulation between preconcentration and

analysis steps, so that analyte losses and risk of contamination are minimized, allowing

higher reproducibility [240]. In addition, all the sample volume is further analyzed, which

enables smaller sample volume to be used. However, in the case of complex samples, off-

line SPE should be preferred due to its greater flexibility, and the opportunity to analyze

the same extract using various techniques.

1.3.8 Challenges

Some of the challenges of preconcentration are as follows:

Preconcentration increases the analysis time and complicates the analysis for large

volume. However, this can be minimized with online systems using flow injection

(FI) techniques because of their potential for automation, minimization of reagent

and/or sample consumption, and reduced risk of contamination. It ffers all

essential prerequisites for trace analysis [241].

It may also lead to losses or contamination of trace elements to be determined.

Special working procedures, reagents of high purity, specially equipped laboratories

and special materials for equipments are necessary.

1.3.9 Common SPE applications

The common SPE application includes:

Metal ions in various complex real samples,

Pharmaceutical compounds and metabolites in biological fluids,

Drugs of abuse in biological fluids,

Environmental pollutants in drinking and waste water,

Pesticides and antibiotics in food/agricultural matrices,

Desalting of proteins and peptides,

Fractionation of lipids, and

Water and fat soluble vitamins

1.4 Types of analytical techniques coupled with preconcentration method

27

Some frequently used analytical techniques in combinations with preconcentration

may be described as follows:

1.4.1 Adsorptive stripping Voltammetry

In trace analysis, mainly of heavy metal ions, Anodic Stripping Voltammetry

(ASV) is popular because of the low limit of determination – ranging to sub ppb

concentrations, its accuracy and precision, as well as the low cost of instrumentation for

this analytical method. ASV is based on previous electrolytical accumulation of the

compound to be determined on the working electrode, followed by voltammetric

dissolution (oxidation) of the reduced substance formed. In addition, some anions or

organic compounds can be accumulated on a mercury electrode to form an insoluble

compound with the mercury ions obtained by dissolution of the mercury electrode at

positive potentials. In this type of cathodic stripping voltammetry (CSV), the reduction

process of the mercury compound on the electrode surface is studied. The most important

step, leading to a substantial increase in the sensitivity in both

types of methods is electrolytic accumulation of the species on the working electrode.

The high sensitivity of adsorptive stripping method is obviously their greatest

advantage. On the other hand, a serious drawback is interference from other surface-

active substances that may be present in the solution. In this case, competitive adsorption

usually occurs and leads to a decrease in the measured current or, at very high surface-

active substance (s.a.s.) concentrations, to significant suppression of the signal.

Interfering effects depend on the nature of both the analyzed and interfering substances

and on their concentration ratio in the determination.

Evidently, the interfering effect of s.a.s. can be minimized by employing short

accumulation times; however, this approach is not suitable in the determination of trace

amounts of analyte. It is then necessary to employ suitable separation of interfering

compounds, e.g. the application of LC or gel chromatography and extraction procedures

[242-244].

1.4.2 X –Ray fluorescence analysis

For the analysis of liquid samples by X-ray fluorescence (XRF) spectrometry, the

liquid in a specially designed liquid sample holder is irradiated directly with X-rays.

However, for direct analysis of liquid samples, the abundance of effective amounts of

analytes in the irradiated volume is insufficient for the determination of trace metals in

natural water. Therefore, for the quantitation of trace metals in aqueous samples by XRF,

28

it is necessary to preconcentrate the analytes through accepted sample pretreatments

[245,246].

In this case, group concentratration, and more rarely individual concentration, is

used and the concentrate should preferably be a solid which can be analyzed directly.

Otherwise, several operations must be successively performed. Thus for example, extracts

are often decomposed and the trace elements sorbed on cellulose powder or silica gel

carrying functional groups. It is more convenient to do the extraction with low-melting

reagents at increased temperature. In this case, the solidified concentrate may at once be

pressed into a tablet and analyzed.

1.4.3 Spectrophotometric determination

Combinations of concentration, especially extractive, with spectrophotometry in

the visible and ultraviolet regions are widely known. Individual concentration steps or

successive separations of several elements are usually used. The matrix is very rarely

separated in this case. Most frequently, the reagent used for concentration also gives a

colored complex with the element to be determined. However, two reagents may also be

used: first, the most selective reagent is used for the separation and then, for the

determination, a reagent which may not be selective but is the most suitable form for the

photometry is employed. The second reagent may also be added after back-extraction or

mineralization of the extract [248-250].

1.4.4 Neutron-activation analysis

There are two distinct ways of trace concentration in this method: before

irradiation and after it. Separation of the matrix before irradiation is necessary if it is

strongly activated and the radioisotopes formed have long half-lives. In the concentration,

trace components which are strongly activated (but are not to be determined) may also be

separated. However, concentration before irradiation nullifies one of the main advantages

of activation analysis-that a blank correction is unnecessary. This advantage is still valid,

however, in the case of concentration after irradiation. In analytical practice, both variants

are used but the second is used more frequently [251-253].

1.4.5 Electrothermal Atomic Absorption Spectrometry

Nowadays, electrothermal atomic absorption spectrometry (ETAAS) is most

powerful and popular analytical tools for the determination of low concentration of metal

ions present in environmental samples and biological materials due to their high

29

selectivity and sensitivity for analyte determination. Nevertheless, they are potentially

prone to spectroscopic and/or non-spectroscopic interferences. Various schemes have

been suggested to alleviate the interfering effects and facilitate reliable analysis such as

protocols ranging from instrument modifications (e.g. background correction) to

experimental designs (e.g. standard addition or internal standardization). However,

instead of implementing such approaches, there is a much simpler and effective solution

to the problem, namely to subject the sample to appropriate pretreatments before it is

presented to the detector. Preconcentration addresses these serious problems for the

determination of metal ions. Concentration of the desired trace elements can extend the

detection limits, remove interfering constituents, and improve the precision and accuracy

of the analytical results [254-256].

1.4.6 Inductively coupled plasma optical emission spectrometry (ICP-OES) Inductively coupled plasma optical emission spectrometry is an analytical

technique often employed to determine metal ions in various types of samples [257]. But,

their sensitivity and selectivity are usually insufficient for direct determination of these

contaminants at a very low concentration level in complex matrix environmental samples.

Moreover, several types of spectral interference have been reported in the determination

of metal ions by ICP-OES. Thus, preconcentration and separation procedures have been

devised to allow trace amounts of metal ions to be determined in complex matrices using

ICP-OES [258,259].

1.4.7 Inductively coupled plasma mass spectrometry (ICP-MS)

Although inductively coupled plasma-mass spectrometry (ICP-MS) capable of the

rapid simultaneous analysis of multiple elements over a large range of concentrations

from a single aliquot of sample, the high salinity concentrations of open ocean samples

can cause substantial salt precipitation and build-up, unpredictable suppression or

enhancement effects as well as mask the analyte signal through the formation of isobaric

and polyatomic interferences due to the presence of high salt content in the samples. In

particular, the matrix elements in the sample can combine with carbon in the atmosphere

and/or argon in the plasma and result in the formation of polyatomic species which may

interfere with the determination of numerous analytes including transition metals and rare

earth elements. In addition, when the sample contains a very high concentration of

dissolved salts, e.g. seawater; clogging of the sample introduction system or of the

injector tube of the torch may occur. Therefore, direct sample injection is impractical,

30

requiring sample pre-treatment to remove the high salinity matrix by either dilution of the

sample or using analyte extraction/separation techniques. Despite the sensitivity of ICP-

MS, open ocean trace metal concentrations are often at or below the detection limit,

prohibiting the further dilution of samples. It is therefore advisable to concentrate and

separate the trace metals from the seawater matrix prior to ICP-MS analysis [260,261].

1.4.8 Inductively coupled plasma atomic emission spectrometry (ICP-AES)

Inductively coupled plasma atomic emission spectrometry (ICP-AES) is widely

recognized as a multi-element technique for the determination of elemental species,

though direct determinations in environmental and biological samples at trace level is

difficult, because the aspiration of solutions with high salt concentrations in the plasma

can cause problems such as blockage of the nebulizer, considerable background emission,

and transport and chemical interferences with a consequent drop in sensitivity and

precision. This limitation can be overcome by using enrichment methods in that metals

ions of interest from solutions are selectively separated and preconcentrated into smaller

volumes to achieve better detection by ICP-AES [262,263].

1.4.9 Atomic absorption spectrometry

Flame atomic absorption is a very common technique for detecting metals and

metalloids in environmental samples [264]. It is a well established technique for the

quantification of nearly 70 elements in a variety of sample types with sensitivity at the

ppm level or less. Aqueous samples can be determined with no sample preparation; solid

samples must be dissolved or digested. This sample preparation for solids can be time

consuming. Although atomic absorption spectroscopy dates to the nineteenth century, the

modern form was largely developed during the 1955s by a team of Australian chemists.

They were led by Alan Walsh and worked at the CSIRO (Commonwealth Science and

Industry Research Organization) Division of Chemical Physics in Melbourne, Australia.

The time since 1955 can be divided into seven years period. The first was an induction

period (1955-1961) when atomic absorption received attention from only a very few

people. This was followed by a growth period (1962-1969) when most of what we see

today was developed, and then by a period of relative stability (1969-1976) when atomic

absorption contributed greatly to other fields. We are now in a period of great change,

which started in about 1876, due to the impact of computer technology on individual

laboratory instruments [265]. Flame atomic absorption spectrometry is among the most

widely used methods for the determination of the heavy metals at trace levels. This

31

technique presents desirable characteristics such as operational facilities, good selectivity

and low cost. However, in the presence of very high excess of diverse ions compared with

the level of analyte, some limitations, mainly those related to the sensitivity are observed.

In trace analysis, therefore, a preconcentration and/or separation of trace elements from

the matrix are frequently necessary to improve the detection limit and selectivity of their

determination [39,266]. Particularly, solid phase extraction has been demonstrated in

various procedures to be a very effective preconcentration technique in combination with

atomic absorption spectrometry. The main advantage of this technique is the possibility of

using a relatively simple detection system with flame atomization instead of a flameless

technique, which require more expensive equipment and are usually much more sensitive

to interferences from macro components of various natural matrices [39].

The technique (Figure 1.4) makes use of absorption spectrometry to assess the

concentration of an analyte in a sample. It relies therefore heavily on Beer-Lambert law.

In short, the electrons of the atoms in the atomizer can be promoted to higher orbitals for

a short amount of time by absorbing a set quantity of energy (i.e. light of a given

wavelength). This amount of energy (or wavelength) is specific to a particular electron

transition in a particular element, and in general, each wavelength corresponds to only

one element. This gives the technique its elemental selectivity.

Principles

As the quantity of energy (the power) put into the flame is known, and the

quantity remaining at the other side (at the detector) can be measured, it is possible, from

Beer-Lambert law, to calculate how many of these transitions took place, and thus get a

signal that is proportional to the concentration of the element being measured.

In order to analyze a sample for its atomic constituents, it has to be atomized. The

sample should then be illuminated by light. The light transmitted is finally measured by a

detector. In order to reduce the effect of emission from the atomizer (e.g. the black body

radiation) or the environment, a spectrometer is normally used between the atomizer and

the detector.

The technique typically makes use of a flame to atomize the sample [267], but

other atomizers such as a graphite furnace [268] or plasmas, primarily inductively

coupled plasma, are also used [269].

Types of Atomizer

32

Figure 1.4 Atomic absorption spectrometer block diagram

When a flame is used it is laterally long (usually 10 cm) and not deep. The height

of the flame above the burner head can be controlled by adjusting the flow of the fuel

mixture. A beam of light passes through this flame at its longest axis (the lateral axis) and

hits a detector.

A liquid sample is normally turned into an atomic gas in three steps:

Analysis of liquids

1. Desolvation (Drying) – the liquid solvent is evaporated, and the dry sample remains.

2. Vaporization (Ashing) – the solid sample vaporises to a gas.

3. Atomization – the compounds making up the sample are broken into free atoms.

The radiation source chosen has a spectral width narrower than that of the atomic

transitions.

Radiation Sources

Hollow cathode lamps are the most common radiation source in atomic absorption

spectroscopy. Inside the lamp, filled with argon or neon gas, is a cylindrical metal

cathode containing the metal for excitation, and an anode. When a high voltage is applied

across the anode and cathode, gas particles are ionized. As voltage is increased, gaseous

ions acquire enough energy to eject metal atoms from the cathode. Some of these atoms

Hollow cathode lamps

33

are in excited states and emit light with the frequency characteristic to the metal [270].

Many modern hollow cathode lamps are selective for several metals.

Atomic absorption spectroscopy can also be performed by lasers, primarily diode

lasers because of their good properties for laser absorption spectrometry [271]. The

technique is then either referred to as diode laser atomic absorption spectrometry

(DLAAS or DLAS) [272], or since wavelength modulation most often is employed,

wavelength modulation absorption spectrometry.

Diode lasers

Interferences

Various factors which may interfere with the determination of metal ions are as follows:

Chemical interferences may also be eliminated by separating the metal from the

interfering material. Although complexing agents are employed primarily to

increase the sensitivity of the analysis, they may also be used to eliminate or reduce

interferences.

The presence of high dissolved solids in the sample may result in interference from

non-atomic absorbance such as light scattering. If background correction is not

available, a non-absorbing wavelength should be checked. Preferably, samples

containing high solids should be extracted.

Ionization interferences occur when the flame temperature is sufficiently high to

generate the removal of an electron from a neutral atom, giving a positively charged

ion. This type of interference can generally be controlled by the addition, to both

standard and sample solutions, of a large excess (1,000 mg/L) of an easily ionized

element such as K, Na, Li or Cs.

Spectral interference can occur when an absorbing wavelength of an element

present in the sample but not being determined falls within the width of the

absorption line of the element of interest. The results of the determination will then

be erroneously high, due to the contribution of the interfering element to the atomic

absorption signal.

Interference can also occur when resonant energy from another element in a

multielement lamp, or from a metal impurity in the lamp cathode, falls within the

band-pass of the slit setting when that other metal is present in the sample. This type

of interference may sometimes be reduced by narrowing the slit width.

34

The interference, known as background absorption, arises from the presence in the

flame of gaseous molecules, molecular fragments and some time smoke. In addition

background effects can be caused by light scatter.

Procedures for reduction of interferences

Ensure if possible that standard and sample solutions are of similar bulk

composition to eliminate matrix effects.

Alteration of flame composition or of flame temperature can be used to reduce the

likelihood of stable compound formation within the flame.

Selection of an alternative resonance line will overcome spectral interferences from

other atom or molecules and from molecular fragments.

Separation, for example by solvent extraction or an ion exchange process, may

occasionally be necessary to remove an interfering element.

The narrow bandwidth of hollow cathode lamps makes spectral overlap rare. That

is, it is unlikely that an absorption line from one element will overlap with another.

Molecular emission is much broader, so it is more likely that some molecular absorption

band will overlap with an atomic line. This can result in artificially high absorption and

an improperly high calculation for the concentration in the solution. Three methods are

typically used to correct this, namely

Background Correction methods

Zeeman correction- A magnetic field is used to split the atomic line into two sidebands.

These sidebands are close enough to the original wavelength to still overlap with

molecular bands, but are far enough not to overlap with the atomic bands. The absorption

in the presence and absence of a magnetic field can be compared, the difference being the

atomic absorption of interest.

Smith-Hieftje correction- The hollow cathode lamp is pulsed with high current, causing a

larger atom population and self-absorption during the pulses. This self-absorption causes

a broadening of the line and a reduction of the line intensity at the original wavelength

[273].

Deuterium lamp correction- In this case, a separate source (a deuterium lamp) with broad

emission is used to measure the background emission. The use of a separate lamp makes

this method the least accurate, but its relative simplicity (and the fact that it is the oldest

of the three) makes it the most commonly used method.

35

1.5 Statistical Treatment of Data

Analytical chemistry besides providing the methods and tools needed for insight

into our material world [274], seeks to improve the reliability of existing techniques to

meet the demands for better chemical measurements which arise constantly in our society

[275]. Statistical analysis is necessary to understand the significance of collected data and

to set limitations on each step of the analysis. The design of experiments is determined

from proper understanding of what the data will represent. It is impossible to perform

chemical analysis that is totally free from errors, or uncertainties. Every measurement is

influenced by many uncertainties, which combine to produce a scatter of results. It is

seldom easy to estimate the reliability of experimental data. However, the probable

magnitude of the error in a measurement can often be evaluated statistically. Limits

within which the true value of a measured quantity lies at a given level of probability can

then be defined.

Chemical analyses are affected by at least two types of errors namely systematic

and random based on their source. Systematic errors have definitive value, assignable

cause and unidirectional of nature. Systematic errors can be reduced to a negligible level

if an analyst pays careful attention to the details of the analytical procedure including

methods, periodic calibration of the instruments and self discipline. Random errors are the

accumulated effect of the individual indeterminate uncertainties. It is caused by the

uncontrollable variables that are an inevitable part of physical and chemical measurement.

It causes the data to scatter more or less symmetrically around the mean in a random

manner which are assumed to be distributed according to the normal error law (Gaussian

curve). They are revealed by small differences in replicate measurements of a single

quantity and affect the precision of the results. They are more difficult for an analyst to

eliminate, but they can be minimized by increasing the number of replicate

measurements. The random error in the result of an analysis can be evaluated by the

method of statistics [276].

The most common applications of statistics to analytical chemistry include:

To establish confidence limits for the mean of a set of replicate data.

To determine the number of replicate measurements required to decrease the

confidence limit for a mean to a given probability level.

To determine at a given probability whether an experimental mean is different from

the accepted value for the quantity being measured (t test or test for bias in an

analytical method).

36

To determine at a given probability level whether two experimental means (different

methods) are different.

To determine at a given probability level whether the precision of two sets of

measurements differs (F test).

To decide whether a questionable data is probably the result of a gross error and

should be discarded in calculating a mean (Q test).

To define an estimate detection limit of a method.

The commonly used terms in the statistical analysis

Mean- The mean (x ) is obtained by dividing the sum of the replicate measurements

(Σxi

) by the number of observations (N) performed in a set. The mean is considered to be

the best estimate of the true value, which can only be obtained if an infinite number of

measurements are performed.

Accuracy- The term accuracy as used in analytical chemical literature is a measure of the

degree to which a mean (x ) obtained from a series of experimental measurements,

agrees with the value, which is accepted as the true or correct value for the quantity. It is

expressed by the error; either absolute or relative error. There are two types of errors

according to their nature and source- systematic errors and random errors. Systematic

error causes the mean of a set of data to differ (unidirectional) from the accepted value.

They have definitive value, assignable cause and affect the accuracy of results. Random

error causes data to be scattered more or less symmetrically around a mean value. It

mainly affects the precision of measurement.

Precision- Precision describes the agreement among the replicate measurements and is

generally expressed as standard deviation, coefficient of variation (relative standard

deviation) and variance.

Standard deviation- Standard deviation(s) measures how closely the data are clustered

about the mean. When measurements are repeated, the scatter of the results will be around

the expected value of the results, if no bias exists.

In analytical chemistry, this scatter is more often than not of such a nature that it can be

described as a normal distribution. The mean gives the centre of the distribution. Standard

deviation measures the width of the distribution. Therefore, an experimental technique

( )2

1−−Σ

=N

xxis

Nix

x∑

=

37

that produces a small standard deviation is more reliable (precise) than one that produces

a large standard deviation provided that they are equally accurate. The square of the

standard deviation, s2

Coefficient of variation- Precision is more often expressed as the coefficient of variation

which is the standard deviation divided by the average and multiplied by 100. Since the

average and standard deviation have same dimension, the coefficient of variation is

dimensionless; it is only a relative measure of precision. Therefore, it is sometimes also

known as relative standard deviation (RSD).

, is known as variance.

Confidence limit and confidence interval- Calculation of s (standard deviation) for a set of

data provides an indication of the precision inherent in a particular method of analysis.

But unless there is a large number of data, it does not by itself give any information about

how close the experimentally determined mean (x ) might be to the true mean value µ

(population mean). Statistical theory, though, allows us to estimate the limits around an

experimentally determined mean(x ) within which the population mean or true value (µ

) expected to lie, within a given degree of probability. The likelihood that the true value

lies within the range is called confidence level or probability usually expressed as a

recent.

Confidence limit for µN

tsx ±=

where t is the student’s t value which depends on the desired confidence level and this

equation holds when σ, population standard deviation is not known.

Correlation coefficient- The correlation coefficient is a measure of the linear relationship

between two variables. In order to establish the linear relationship between variables xi

and yi

RSD sx

= ×100

the Pearson’s correlation coefficient r is used. The r may have values between +1

and –1. When the r is +1, there is a perfect correlation, i.e. an increase in one variable is

associated with an increase in the other. When the r is –1, there is perfect negative

correlation, i.e., one variable increases where as the other decreases. When r is zero, one

variable has no linear relationship to the other. The correlation coefficient r is calculated

by using the above equation.

( )[ ] ( )[ ]r

n x y x y

n x x n y yi i i i

i i i i

=−

− −

Σ Σ

Σ Σ Σ Σ2 2 2 2

38

Regression equation- When two variables exhibit a linear relationship, we may be

interested in quantifying the relationship so that a value of one variable may be estimated

from the other. A common example is the construction of calibration curve, which relates

the concentration of analyte to absorbance or any measurable property. The least square

curve fitting technique is the most commonly accepted mathematical procedure known

for this purpose. The equation derived by this technique produces a line whose position is

such that the sum of the squares of the vertical distances of each data point to the line is a

minimum if the line is to be used to predict y from x values, or the sum of the squares of

the horizontal distances is a minimum if x is to be predicted from y. If y = bx + a

represents the equation for a straight line, where y is dependent variable and x is

independent variable, then slope ‘b’ and intercept ‘a’ are derived from the following

equations [276-278].

Sensitivity- It is measure of the ability of an instrument or method to discriminate between

small differences in analyte concentration. There are two factors which limit the

sensitivity:

the slope of the calibration curve.

reproducibility or precision of the measuring device.

Of two methods that have equal precision, the one that has the steeper calibration

curve will be the more sensitive. A corollary to this statement is that if two methods have

calibration curves with equal slopes, the one that exhibits the better precision will be the

more sensitive. The quantitative definition of sensitivity that is accepted by the

International Union of Pure and Applied Chemists (IUPAC) is calibration sensitivity,

which is the slope of the calibration curve at the concentration of interest. Most

calibration curves that are used in analytical chemistry are linear and may be represented

by the equation: S = mc + Sbl, where S is the measured signal, c is the concentration of

the analyte, Sbl is the instrumental signal of the blank, and m is the slope of the straight

line. The quantity Sbl

( )b

n x y x yn x x

i i i i

i

=−

−

Σ Σ Σ

Σ Σ2 2

should be the intercept of the straight line. With such curves, the

calibration sensitivity is independent of the concentration c and is equal to m. The

calibration sensitivity as a figure of merit suffers from its failure to take into account the

precision of individual measurements.

a y bx= −

39

To include precision in a meaningful mathematical statement of sensitivity,

analytical sensitivity is proposed (γ): γ = m/ss; where ss = standard deviation of

measurement and m is the slope of the calibration

curve [270,279].

Detection limits- It is defined as the minimum concentration or mass of analyte that can

be detected at a known confidence level. This limit depends upon the ratio of the

magnitude of the analytical signal to the size of the statistical fluctuations in the blank

signal. The limit of detection (CL) according to the definition of International Union of

Pure and Applied Chemists can be expressed as [280]: CL = x + k.sbl ; where x = mean of

blank signal, sbl

The estimation of the detection limit is best understood by considering a

calibration graph. Using the linear regression method, it is possible to obtain the intercept

and slope of the best-fit line. The value of the intercept can be used as x; and errors in the

slope and the intercept of the regression line is acceptable as a measure of s

= standard deviation of the blank measures and k = numerical constant. A

value of k=3 was strongly recommended by IUPAC. The Analytical Methods Committee

of the Royal Society of Chemistry sought to clarify the IUPAC definition [281].

bl. Hence, the

detection limit (CL) may also be expressed as: CL = 3sbl

/b; where b is the slope of the

calibration line [270,277,282,283].

1.6 Present work and its scope

SPE has found its most effective use as a sample clean-up and concentration

method prior to further analysis. Solid phase extraction, in combination with atomic

absorption spectrometry, has been developed as the technique for preconcentration prior

to determination of trace metal ions in varying complex matrices, which includes both

biological and environmental samples.

Amberlite XAD-4 and 16 resins have been successfully used as the polymeric

supports in previous works (Table 1.2 and 1.3). Hence, we have used the same because of

its good surface area (725 m2 g-1 and 800 m2 g-1) and high porosity. The functional groups

used satisfactorily for this work are salicylic acid, o-hydroxybenzamide, salicylanilide

and p-aminobenzene sulfonic acid on account of their smaller size and good number of

chelating sites. This functionalities would render the modified resin more hydrophilic so

as to facilitate faster equilibrium (of solute between solid and aqueous phases) whereby

enhancing the extraction ability.

40

The modification of polystyrene-divinyl benzene adsorbent resin has been

accomplished through azotization reaction, by conventional reaction techniques, by

incorporating neutral organic hydrophilic group through –N=N- spacer. It is important to

note that these functional groups are neutral, that is they bear no positive or negative

charge but, however, they possess the characteristic features of a chelating agent. This is

important in order to allow for effective contaminant removal of the inorganics since

either anionic or cationic charged resins may often pick up undesirable materials that are

present such as other matrices. However, neutral functionalized or modified resins such as

those described here in act differently than charged resins and take up the inorganics by

adsorbtion/chelation rather than ion exchange.

Chelating resin and the aqueous solution containing the heavy metals along with

other matrices may be contacted using both batch and column methods which would

result in intimate contact between the resin and the solution. The columns used for

extractions were packed with 100 to 500 mg of resin. Varying volume of aqueous

solutions of a sample, containing metals in the concentration of the order of parts per

million, is passed through the column at the optimum flow rate whereby the solute gets

retained onto the resin.

Investigations of the optimum experimental conditions sorption and elution have

been carried out by considering the following influential parameters.

Synthesis and Characterization

The introduction of the organic groups onto the polymeric material (XAD-series

resin) can make the stable chelating compounds for the uptake of trace metal ions. The

aim of chemical modification with different organic reagent, which has mainly N and O

donor atoms, is to make the material have excellent coordination properties with trace

metal ions and to obtain a novel sorbent with high loading of metal ions. The FT-IR

analysis is a very useful technique in identifying the immobilization process by

comparing the precursor and modified resin. The thermogravimetric analysis (TGA)

curve of the chelating resin shows mass loss in two steps. In first step, it may be due to

the loss of sorbed water of the resin and second step, due to the loss of functional moieties

of the chelating resin. It was also use to performed, to study the water-regaining capacity

of the resin matrix in order to evaluate its hydrophilic character. The CHN analysis was

performed during each stage of chemical modification to study the extent of ligand

functionalization to the polymeric matrix.

41

The modified resin soaked in acidic (HCl/HNO3, 1-5 mol L-1) and basic medium

(NaOH, 1-4 mol L-1) for 6 h, filtered and then washed with triply distilled water until free

from acid or alkali. The resin shows no loss in sorption capacity. Hence, the resin

exhibited high chemical stability. The water regain capacity and hydrogen ion capacity

have also been studied. This value reflects the high hydrophilicity of the resin which is

satisfactory for column operation. In case of AXAD-16-SALD, the overall hydrogen ion

capacity amounts to 6.08 mmol g-1 of resin, which may be contributed both by the

hydroxylic and amide groups present within the molecule. Theoretically, if 2.65 mmol of

the reagent constituted per gram of the resin, the hydrogen ion capacity, due to the

hydroxylic group should have been 2.65 mmol g-1

. The durability and reusability nature

of the chelating resin was tested with metal ions solutions by batch equilibration method.

Thereafter, the sorption and desorption of metal ions were repeated on the same resin.

The capacity of the resin found to be constant up to the several cycles (35-55) showing

the multiple use of chelating resin without any loss in its physical and chemical

properties.

Sorption studies

Effect of pH of the sample

Sample pH is of prime importance for efficient retention of the trace elements on

the sorbent. Its influence strongly depends on the nature of the sorbent used. Careful

optimization of this parameter is thus crucial to ensure quantitative retention of the trace

elements and in some cases selective retention. In particular with ion exchangers, correct

adjustment of sample pH is required to ensure preconcentration. Thus, in the case of

cationic-exchangers, low pH usually results in poor extraction due to competition

between protons and cationic species for retention on the sorbent. When retention of trace

elements is based on chelation (either in the sample or on the solid sorbent), the sample

pH is also a very important factor as most chelating ligands are conjugated bases of weak

acid groups and accordingly, they have a very strong affinity for hydrogen ions. The pH

will determine the values of the conditional stability constants of the metal complexes. By

contrast, pH may have no influence with some non-ionizable organic ligands [284]. For

inorganic oxides, pH is also of prime importance. In particular, on amphoteric oxides

such as TiO2 or Al2O3

, cations are adsorbed at elevated pH due to the deprotonation of

functional groups, whereas anion retention requires acidic conditions for the protonation

of functional groups.

42

Adsorption isotherm

The isotherm parameters of Langmuir and Frendlich for the sorption of metal ions

have been studied. The results showed that the regression coefficients R2

obtained from

Langmuir model were very close to 1, suggesting the Langmuir model could well

interpret the studied adsorption procedure. From the comparison of correlation

coefficients, it can be concluded that the data were fitted better by Langmuir equation

than by Freundlich equation. Langmuir equation is applicable to homogeneous

adsorption, where the adsorption of each adsorbate molecule onto the surface had equal

adsorption activation energy. The fact shows that the adsorption of the hybrid sorbent is

attributed to monolayer adsorption [285].

Kinetics of sorption

In order to determine the uptake rate of metal ions on the synthesized resin and get

access to the equilibrium time, studies on sorption kinetics were carried out. The

sorbents characterized by good kinetic properties determined by the macroporous

structure of the support, large surface area and total accessibility of the functional groups

(without steric hindrance). The kinetic studies also showed that the temperature affected

the rate constants significantly, that is, saturation was reached at a faster rate at higher

temperature. This temperature effect may be a manifestation of the fact that the resin

swells more completely at higher temperature, which allows metal ions to diffuse more

easily into the interior of the resin, and that the sorption was an endothermic process and

hence high temperature facilitates higher sorption. Moreover, both pseudo-first-order

equation and pseudo second- order equation were used to express the sorption process of

the chelating resin. The results showed that regression coefficients values (R2

) of the

pseudo-second-order model (>0.99) were better than those of the pseudo-first-order

model for the sorbent, suggesting the pseudo-second-order model was more suitable to

describe the sorption kinetics of chelating resin [285,286].

Sample flow-rate

The sample flow-rate has been optimized to ensure quantitative retention along

with minimization of the time required for sample processing. This parameter may have a

direct effect on the breakthrough volume, and elevated flow-rates may reduce the

breakthrough volume [284]. As a rule, cartridges and columns require lower maximum

flow-rates than disks ranging typically from 0.5 to 5 mL min-1. This value may be

43

increased by a factor of 10 using disks. High flow rate has been found for the sorption of

metal ions, such high flow rates support the superiority of present chelating resins.

Elution studies

Nature of the eluent

The nature of the eluent is of prime importance and should optimally meet three

criteria: efficiency, selectivity and compatibility, as discussed below. In addition, it may

be desirable to recover the analytes in a small volume of eluent to ensure a significant

enrichment factor. The eluent may be an organic solvent (when reversed-phase sorbents

are used), an acid (usually with ion-exchangers), or a complexing agent. Firstly, the

eluting agent has been carefully chosen to ensure efficient recovery of the retained target

species and quantitative recovery as far as possible [287]. A further characteristic of the

eluent arises with the possibility of introducing selectivity. Using an eluent with a low or

moderate eluting power, the less retained analytes can be recovered without eluting the

strongly retained compounds. Thus, if the elements of interest are those that remain on the

sorbent another elution step with a more eluent will ensure their quantitative recovery. In

that way interfering analytes were removed during the first eluting step (also called

washing step). On the opposite, if the compounds of interest are the less retained on the

sorbent their elution with a low or moderate eluting agent ensures their selective recovery,

as the interferent compounds will remain on the sorbent due to stronger interactions with

the solid support. In some cases, this selectivity may favour speciation. For example, 1

mol L-1 HCOOH removed only Se4+ from an anion-exchange resin, leaving Se6+ retained

on the sorbent, which was further eluted using 2 mol L-1 HCl [104]. Finally, the eluent

should be compatible with the analysis technique. In particular, when using both flame

and electrothermal AAS, HNO3 has been preferred to other acids (namely H2SO4

, HCl),

as nitrate ion is a more acceptable matrix [288].

Effect of pH of eluent

As retention of trace elements on solid sorbents is usually pH-dependent, careful

choice of the eluent pH may enhance selectivity in the SPE procedure. As an example,

once retained on Eriochrome black-T (ERT)-functionalized- silica gel, Mg2+ could be

eluted first at a pH approximately 4, while increasing the pH to 5–6 was required for

eluting Zn2+

[237].

44

Elution mode

Most of the time, for practical reasons, sample loading and elution steps are

performed in a similar manner. However, to avoid irreversible adsorption and ensure

quantitative recoveries, elution in the back flush mode is recommended in some cases.

This means that the eluent is pumped through the sorbent in the opposite direction to that

of the sample during the preconcentration step. This is especially crucial when carbon-

based sorbents have to be used due to possible irreversible sorption of the analytes.

Flow-rate of eluent

The flow-rate of the elution was found to be high enough to avoid excessive

duration, and low enough to ensure quantitative recovery of the target species. Typical

flow-rates are in the range of 0.5 to 5 ml min-1 for cartridges/ columns and of 1 to 20 ml

min-1

for disks [289]. As a rule, the higher the flow-rate, the larger the eluent volume

required for complete elution [290,291].

Volume of Eluent

The elution volume may be determined either experimentally or estimated

theoretically [292]. The elution volume can usually be reduced by increasing the

concentration of the eluent (e.g. acid). However, in this case, problems with subsequent

analysis may be encountered (e.g. FAAS). Alternatively, the use of micro-sized disks may

allow reduced solvent volume [293]. The elution step should enable sufficient time and

elution volume to permit the metallic species to diffuse out of the solid sorbent pores. As

a rule, 2 elution cycles are usually recommended as compared to a single step (e.g. two 5

ml elution should be preferred to a single 10 ml elution). Soaking time is also critical and

2 to 5 minute soak is most of the time allowed before each elution.

Breakthrough profile

Sample volume to be percolated

An important parameter to control in SPE is the breakthrough volume, which is

the maximum sample volume that has been percolated through a given mass of sorbent

after which analytes start to elute from the sorbent resulting in non-quantitative recoveries

(Figure 1.5). The breakthrough volume is strongly correlated to the chromatographic

retention of the analyte on the same sorbent and depends on the nature of both the sorbent

and the trace element, as well as on the mass of sorbent considered and the analyte

concentration in the sample [294]. In addition, it depends on the sorbent containers, as

45

disks usually offer higher breakthrough volumes than cartridges. This volume may be

determined experimentally or estimated using several methods [292]. For that purpose the

nature of the sample has to be taken into account, as the possible presence of ligands may

dramatically reduce the breakthrough volume [295].

Figure 1.5 Typical representation of the breakthrough curve (i.e. concentration of

the analyte at the outlet of the SPE system vs. sample volume percolated through the system).

VB is the breakthrough volume, VR the chromatographic elution volume, VC the sample

volume corresponding to the retention of the maximum amount of analyte and C0

Preconcentration is a process in which the ratio of the quantity of a desired trace

element to that of original matrix is increased but it does not necessarily mean increase in

the concentration of the analyte. In order to demonstrate the preconcentration factor,

preconcentration limit column procedure has been applied. The closeness of the dynamic

capacity to the total sorption capacity reflects the applicability of the column technique

for preconcentration.

is the

initial analyte concentration in the sample.

Interference of sample matrix

The presence of ligands in the sample matrix may affect trace element retention

when stable complexes are formed in the sample with these ligands, as trace elements are

less available for further retention. Thus, if metals are present in the sample as strong

complexes, they may not dissociate resulting in no retention of the free metal on the

sorbent. As an example, reduction in the retention of Cu2+ on Amberlite CG50 occurs in

the presence of ligands such as glycine [296]. In the case of real samples, the presence of

natural organic matter is of great concern as it may form complex with trace elements as

observed for Cu2+ [296,297]. The most important class of complexing agents that occurs

46

naturally are the humic substances [298]. Their binding of metals through chelation is one

of the most important environmental qualities. Yet, in some cases the presence of ligands

may be a valuable tool for adding selectivity to the SPE step. This requires that the added

ligands be correctly chosen to complex only the elements that are not of interest so that

they are not retained on the sorbent [235]. The presence of ions other than the target ones

in the sample may also cause problems during the SPE step. In particular, due to their

usually high levels (e.g. Ca2+

), they may hinder the preconcentration step by overloading

the sorbent or cause interferences during spectrophotometric analysis. Therefore, their

influence has been studied before validating a SPE method. Sometimes the addition of a

proper masking agent (such as EDTA, thiourea or ethanolamine for example) may

prevent the formation of interferences due to ions present in the sample [287]. Finally, the

ionic strength of the sample is another parameter to control for an efficient SPE, as it may

influence the retention of trace elements, and thus the value of the breakthrough volume

for a given sorbent [299,300]. The chelating resin was found to tolerate high contents of

various naturally occurring alkali and alkaline earth metals, anions and complexing agents

in the determination of these metal ions.

Analytical method validation

Great care has been taken to ensure that accurate results are obtained in the

analysis. Every measurement has some imprecision associated with it, which results in

random distribution of results. The experiment can be designed to narrow the range of

this (confidence limit is set around the mean at some degree of probability), but it cannot

be eliminated. Precision of the method is expressed either standard deviation or relative

standard deviation. Systematic errors of instrumental and personal type are minimized by

periodic calibration of the instruments and volumetric glassware, and self-discipline.

However, systematic method errors are difficult to detect and introduces bias in the

method. Bias of the analytical method has been estimated by the following procedures:

Analyzing Standard Reference Materials (SRM) of biological, environmental and alloy

type having complex sample matrix obtained from National Institute of Environmental

studies (NIST), Iron and Steel institute of Japan (JSS) and National bureau of Standards

Using a Second Independent and Reliable Analytical Method in parallel with the method

being evaluated when standard samples are not available. The independent method should

(NBS). In order to demonstrate whether the difference of the observed mean of the

replicate analysis of SRM and its certified value is due to merely the random error of the

measurement or bias in the method, statistical t test is applied.

47

differ as much as possible from the one under study. This minimizes the possibility that

some common factor in the sample has the same effect on both methods. Then a statistical

t and f test must be used to determine whether any difference is a result of random errors

in the two methods or due to bias in the method under study.

Performing Recovery Experiment which requires the spiking of the sample with known

amounts of the analyte. The amount determined (recovered) by the method is expressed in

terms of percentage recovery which shows accuracy of the developed method. By varying

the sample size, the presence of a constant error can be detected.

Applications

In order to explore the potential applicability of the chelating resin the developed

methods were successfully applied for the determination of metal ions in natural and

sewage water, mint leaves, mango pulp, fish, urine, multivitamins tablets, infant milk

substitute and hydrogenated oil (ghee).

1.7 Merits of the present work

The main advantage of the present procedure is the simple and fast preparation of

the chelating resin and no requirement of organic solvents in the metal elution step.

The excellent ability for the exclusion of alkali and alkaline earth elements makes it

desirable for use in the separation and preconcentration of trace elements because

their presence often interfere in the subsequent FAAS determination.

The use of a column preconcentration technique allows for the assessment of low

trace metal concentrations, even by less sensitive determination methods such as

FAAS.

Preconcentration by this material from river water samples do not require any prior

digestion of the samples. It can be successfully applied for the analysis of both

environmental and biological samples as indicated by the high precision (low

relative standard deviation).

The designing and characterization of these four Amberlite XAD-4/16 based

chelating resins and the investigation of their metal sorption behavior with their

subsequent applications for analysis of various real samples containing varying complex

matrices define the scope of the present thesis.

48

Table 1.2 Chelating agents used for modification of Amberlite XAD-4 resin

Reagent Mode of

preparation Techniques coupled Metals Ref.

N-(dithiocarboxy)- sarcosine Chelate

complex Spectrophotometry Co 301 2+

8-Hydroxyquinoline (Oxine) Impregnation Spectrophotometry UO2 302 2+

o-Aminobenzoic acid Chemically

modified FAAS Pb2+,Cd2+,Ni2+, Co2+,Zn 303 2+

2,3-Dihydroxy-naphthalene Chemically

modified ICP-AES Cu2+, Ni2+, Co2+, Cd 304 2+

Ammoniumpyrrolidine-

dithiocarbamate Impregnation ICP-AES

Cd2+,Cu2+,Mn2+,Ni2+,Pb2+,

Zn305 2+

2-Acetylmercapto-

phenyldiazoaminoazobenzene

Chelate

complex FAAS Cd2+,Co2+,Cu2+,Ni2+, Zn 306 2+

2,6-dihydroxyphenyl-

diazoaminoazobenzene

Chelate

complex FAAS Cd2+, Co2+, Cu2+, Zn 307 2+

Diethyldithiocarbamates Chelate

complex FAAS

Cu2+, Fe2+, Pb2+, Ni2+,

Cd2+, Bi308 2+

1-Hydrazinophthalazine Chelate

complex AAS

Cd2+, Co2+,Cu2+, Ni2+,

Pb2+, Fe2+, Cr3+Zn309 2+

1-(2-pyridylazo)-2-naphthol Impregnation FI-FAAS Cu 234 2+

1-(2-pyridylazo)-2-naphthol Chelate

complex AAS

Cd2+, Cu2+, Ni2+, Pb2+,

Cr3+, Mn310 2+

Salen Chemically

modified AAS Cu2+, Pb2+, Bi 311 2+

Succinic acid Chemically

modified Spectrophotometry U 312 6+

Schiff bases Chemically

modified FI–FAAS

Cd2+, Co2+, Cu2+, Ni2+,

Pb313 2+

O,O-Diethyldi-thiophosphate Chelate

complex FI-FAAS Cd 314 2+

m-Phenylendi-amine Chemically

modified ICP-AES

Rh

3+ 315

2,3-Diamino-naphtalene Chemically

modified Se 316 6+

Chemically

modified 2-Aminothiophenol FAAS Cd2+, Ni 317 2+

49

Table 1.3 Chelating agents used for modification of Amberlite XAD-16 resin

Reagent Mode of

preparation

Techniques coupled Metals Ref.

1,6-bis(2-carboxy

aldehydephenoxy)butane

Chemically

modified FAAS Cu2+, Cd 318 2+

2,6-dichlorophenyl-3,3-

bis(indolyl)methane Impregnation FAAS Cu2+,Zn2+, Mn 319 2+

Gallic acid Chemically

modified FAAS Cr3+,Mn2+,Fe3+,Co2+,

Ni2+, Cu320

2+ 4-{[(2-hydroxyphenyl)imino]

methyl}-1,2-benzenediol Chemically

modified FAAS

Zn2+, Mn2+, Ni2+, Pb2+,

Cd2+, Cu2+, Fe3+, Co164 2+

Acetylacetone Chemically

modified AAS Cr 3+, Cr 321 6+

3,4-dihydroxy benzoyl methyl

phosphonic acid

Chemically

modified FAAS U6+ ,Th4+ 322

Phthalic acid Chemically

modified AAS Pb 323 2+

N,N-dibutyl-N_-

benzoylthiourea Impregnation Spectrophotometry U6+ 160

(bis-2,3,4-trihydroxybenzyl)

ethylene diamine

Chemically

modified Spectrophotometry U6+, Th4+, Pb2+, Cd 162 2+

Thiocyanate Impregnation FAAS Ag 324 2+

1,5-diphenylcarbazone Impregnation FAAS Cr6+ ,Cr 325 3+

Nitrosonaphthol Chemically

modified AAS Ni2+, Cu 165 2+

50

References

[1] E.S. Deevey, Mineral Cycles. In: The Biosphere. A Scientific American Book, 1970, p. 83.

[2] G.D. Guthrie Jr., Biological effects of inhaled minerals. Am. Mineral 77 (1992) 225.

[3] W.S. Fyfe, Toward 2050: the past is not the key to the future- challenges for the science of geochemistry, Environ Geol. 33 (1998) 92.

[4] H. Hu, Exposure to metals, Prim. Care 2 (2000) 983.

[5] B.A. Chowdhury, R.K. Chandra, Biological and health implications of toxic heavy metal and essential trace element interactions, Prog. Food Nutr. Sci. 11 (1987) 55.

[6] H. Hu, Heavy metal poisoning, in: Harrison’s Principles of internal medicine, Mc Graw-Hill, Medical Publishing Divison, New York, vol. 2, 16th

[7] D. Bellinger, A. Leviton, C. Waternaux, H. Needleman, M. Rabinowitz,

edn, 2005, p. 2577.

Longitudinal Analyses of Prenatal and Postnatal Lead Exposure and Early Cognitive Development, New Engl. J. Med. 316 (1987) 1037.

[8] J.M. Schwartz, B.S. Simon, D.B. Roche, K. Stewart, W.F. Characterization of toxicokinetics and toxicodynamics with linear systems theory: application to lead-associated cognitive decline, Environ. Health Perspect. 109 (2001) 361.

[9] WHO, Lead in drinking-water. Background document for preparation of WHO Guidelines for drinking-water quality. World Health Organization, Geneva, 2003 (WHO/SDE/WSH/03.04/9).

[10] L. Friberg, Handbook on the Toxicology of Metals. Vol. I: General Aspects. Elsevier, Amsterdam, 1986.

[11] R.B. Martin, Metal Ion Toxicity, in: Encyclopedia of Inorganic Chemistry, Robert H. rabtree (Ed), John Wiley & Sons, 2006.

[12] E.A. Boyle, in: J.O. Nriagu (Ed), Copper in the environment, Wiley, New York, 1979.

[13] D.L. Nelson, M.M. Cox, Lehninger, Principles of Biochemistry, 3rd

[14] L.G. Cockerham, B.S. Shane, Basic Environmental Toxicology, CRC Press, Boca Raton, Ann Arbor, London, 1994.

Edn., Worth Publishing, New York, 2000.

[15] International agency for research on cancer (IARC), in: Proceedings of the meeting of the IARC working group on beryllium, cadmium, mercury and exposures in the glass manufacturing industry, Scand. J. Work. Environ. Health. 19 (1993) 360.

[16] J.H. Martin, G.A. Knauer, A.R. Flegal, in: J.O. Nriagu (Ed), Cadmium in the environment, Wiley, New York, 1979.

51

[17] M. Stoeppler, Analysis of nickel in biological materials and natural waters, in: J.O. Nriagu (Ed.), John Wiley, New York, 1980.

[18] E. Nieboer, D.M. Templeton, Nickel biogeochemistry, Sci. Total Environ. 148 (1994) 109.

[19] W.E. Davis, National Inventory of Sources and Emissions of Cadmium, Copper, Nickel and Zinc, Report no. PB-210678, National Techn. Info. Service, Springfield, 1972.

[20] C. Baird, Environmental Chemistry, W.H. Freeman and Company, New York, 1995.

[21] S.E. Manahan, Environmental Chemistry, Lewis Publisher-CRC Press, Boca Raton, 6th

[22] B. Weiss, P.J. Landrigan, The developing brain and the environment: an introduction, Environ. Health Perspect. 108 (2000) 373.

edn. Florida, 1994.

[23] P. Bulat, Activity of Gpx and SOD in workers occupationally exposed to mercury, Arch. Occup. Environ. Health 71 (1998) 37.

[24] S.J. Stohs, D. Bagchi, Oxidative mechanisms in the toxicity of metal ions, Free Radic. Biol. Med. 18 (1995) 321.

[25] D. Jay, Glutathione inhibits SOD activity of Hg, Arch. Inst. Cardiol. Mex. 68 (1998) 457.

[26] WHO, Environmental Health Criteria 101: Methyl Mercury. World Health Organization, Geneva, 1990.

[27] B. Weiss, Vulnerability of children and the developing brain to neurotoxic hazards. Environ. Health Perspect. 108 (2000) 375.

[28] IARC, Monograph on the evaluation of carcinogenic risk to humans, vol. 49. Chromium, Nickel and welding. International Agency for Research on Cancer, Lyon, 1990.

[29] J.O. Nriagu, Global inventory of natural and anthropogenic emissions of trace metals to the atmosphere, Nature 279 (1979) 409.

[30] K. Prabhakaran, D. Ghosh, G.D. Chapman, P.G. Gunasekar, Molecular mechanism of manganese exposure-induced dopaminergic toxicity, Brain Res. Bull. 76 (2008) 361.

[31] J. Crossgrove, W. Zheng, Manganese toxicity upon overexposure, NMR Biomed. 17 (2004) 544.

[32] M. Saric, Manganese. Handbook on the toxicology of metals, vol. II: Specific metals, Elsevier Science Publishing Co; New York, 1986. p. 354.

[33] ASTDR. Toxicological profile for manganese. Atlanta Georgia: US Department of Health and Human Services, Agency for Toxic Substances and Disease Registry; 2000. p. 1.

52

[34] A. Street, W. Alexander, Metals in the Service of Man, 4th edn, Penguin, London, 1962.

[35] Ullman’s Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim, 2003.

[36] P.T. Lieu, M. Heiskala, P.A. Peterson, Y. Yang, Molecular Aspects of Medicine, 22 (2001) 1.

[37] D.J. Weatherall, J.B. Clegg (Eds.), The Thalassemia Syndromes, Blackwell Scientific Publication, Oxford, 1981.

[38] A.E. Martell, R.D. Hancock, Metal Complexes in Aqueous Solutions, Plenum Press, New York, 1996.

[39] K. Pyrzynska, M. Trojanowicz, Functionalized cellulose sorbents for preconcentration of trace metals in environmental analysis, Crit. Rev. Anal. Chem. 29 (1999) 313.

[40] Y.C.J. Kantipuly, A.D. Westland, Review of methods for the determination of lanthanides in geological samples, Talanta 35 (1988) 1.

[41] C. Karadas, D. Karaa, A. Fisher, Determination of rare earth elements in seawater by inductively coupled plasma mass spectrometry with off-line column preconcentration using 2,6-diacetylpyridine functionalized Amberlite XAD-4, Anal. Chim. Acta 689 (2011) 184.

[42] S. Qian, Z. Huang, J. Fu, J. Kuang, C. Hu, Preconcentration of ultra-trace arsenic with nanometre-sized TiO2 colloid and determination by AFS with slurry sampling, Anal. Methods 2 (2010) 1140.

[43] M. Grabarczyk, A. Koper, Selective, sensitive and economical method for the adsorptive voltammetric determination of trace amounts of Mo(VI) in organic matter rich environmental sample, Talanta 84 (2011) 393.

[44] W.R.L. Cairns, A. De Boni, G. Cozzi, M. Asti, E.M. Borla, F. Parussa, E. Moretto, P. Cescon, C. Boutron, J. Gabrieli, C. Barbante, The use of cation exchange matrix separation coupled with ICP-MS to directly determine platinum group element (PGE) and other trace element emissions from passenger cars equipped with diesel particulate filters (DPF), Anal. Bioanal. Chem. 399 (2011) 2731.

[45] D. Kara, A. Fisher, S. J. Hill, Comparison of some newly synthesized chemically modified Amberlite XAD-4 resins for the preconcentration and determination of trace elements by flow injection inductively coupled plasma-mass spectrometry (ICP-MS), Analyst 131 (2006)1232.

[46] F. Sabermahani, M.A. Taher, Flame atomic absorption determination of palladium after separation and preconcentration using polyethyleneimine water-soluble polymer/alumina as a new sorbent, J. Anal. At. Spectrom. 25 (2010) 1102.

[47] Y.A. Zolotov, Preconcentration In Inorganic Trace Analysis, Pure & Appi. Chem. 50 (1978) 129.

53

[48] S. Kagaya, E. Maeba, Y. Inoue, W. Kamichatani, T. Kajiwara, H. Yanai, M. Saito, K. Tohda, A solid phase extraction using a chelate resin immobilizing carboxymethylated pentaethylenehexamine for separation and preconcentration of trace elements in water samples, Talanta 79 (2009) 146.

[49] S. Sadeghi, E. Sheikhzadeh, Solid phase extraction using silica gel modified with murexide for preconcentration of uranium (VI) ions from water samples, J. Hazard. Mater. 163 (2009) 861.

[50] T. Madrakian, M. A. Zolfigol, M. Solgi, Solid phase extraction method for preconcentration of trace amounts of some metal ions in environmental samples using silica gel modified by 2,4,6-trimorpholino-1,3,5-triazin, J. Hazard. Mater. 160 (2008) 468.

[51] M. Ghaedi, B. Karami, S. Ehsani, F. Marahel, M. Soylak, Preconcentration-separation of Co(II), Ni(II), Cu(II) and Cd(II) in real samples by solid phase extraction of a calix[4] resorcinarene modified Amberlite XAD-16 resin, J. Hazard. Mater. 172 (2009) 802.

[52] M. Ezoddin, F. Shemirani, Kh. Abdi, M. Khosravi Saghezchi, M.R. Jamali, Application of modified nano-alumina as a solid phase extraction sorbent for the preconcentration of Cd and Pb in water and herbal samples prior to flame atomic absorption spectrometry determination, J. Hazard. Mater. 178 (2010) 900.

[53] X. Huang, X. Chang, Q. He, Y. Cui, Y. Zhai, N. Jiang, Tris(2-aminoethyl) amine functionalized silica gel for solid phase extraction and preconcentration of Cr(III), Cd(II) and Pb(II) from waters, J. Hazard. Mater. 157 (2008) 154.

[54] Z. Li, X. Chang, Z. Hu, X. Huang, X. Zou, Q. Wu, R. Nie, Zincon-modified activated carbon for solid phase extraction and preconcentration of trace lead and chromium from environmental samples, J. Hazard. Mater. 166 (2009) 133.

[55] A.S. Pereira, G. Ferreira, L. Caetano, M.A.U. Martines, P.M. Padilha, A. Santos, G.R. Castro, Preconcentration and determination of Cu(II) in a fresh water sample using modified silica gel as a solid phase extraction adsorbent, J. Hazard. Mater. 175 (2010) 399.

[56] I. Lopez-Garcia, P. Vinas, R. Romero-Romero, M. Hernández-Cordoba, Preconcentration and determination of boron in milk, infant formula, and honey samples by solid phase extraction-electrothermal atomic absorption spectrometry, Spectrochimica Acta Part B 64 (2009) 179.

[57] A.A. Ensafi, A.Z. Shiraz, On-line separation and preconcentration of lead(II) by solid phase extraction using activated carbon loaded with xylenol orange and its determination by flame atomic absorption spectrometry, J. Hazard. Mater. 150 (2008) 554.

[58] M. Faraji, Y. Yamini, S. Shariati, Application of cotton as a solid phase extraction sorbent for on-line preconcentration of copper in water samples prior to inductively coupled plasma optical emission spectrometry determination, J. Hazard. Mater. 166 (2009) 1383.

54

[59] Jing Fan, Chunlai Wu, Haizhu Xu, Jianji Wang, Chuanyun Peng, Chemically functionalized silica gel with alizarin violet and its application for selective solid phase extraction of lead from environmental samples, Talanta 74 (2008) 1020.

[60] R. Gao, Z. Hu, X. Chang, Q. He, L. Zhang, Z. Tu, J. Shi, Chemically modified activated carbon with 1-acylthiosemicarbazide for selective solid phase extraction and preconcentration of trace Cu(II), Hg(II) and Pb(II) from water samples, J. Hazard. Mater. 172 (2009) 324.

[61] J. Pawliszyn (Ed), Sampling and sample preparation in field and laboratory: fundamentals and new directions in sample preparation, in: Comprehensive analytical chemistry, D. Barcelo (Ed), vol. 37, Elsevier B.V., 2002.

[62] T. Braun, G. Gersini (Eds), Extraction chromatography, Akaddmiai Kiadd, Budapest, 1975.

[63] Y. Sekizura, T. Kojima, T. Yano, K. Ueno, Analytical application of organic reagents in hydrophobic gel media-I: General principle and the use of dithizone gel, Talanta 20 (1973) 979.

[64] S. Mitra, Sample preparation techniques in analytical chemistry, in: Chemical analysis: A series of monographs on analytical chemistry and its applications, J. D. Winefordner (Ed), vol. 162, John Wiley & Sons, Inc., Hoboken, New Jersey, 2003.

[65] I. Komjarova, R. Blust Comparison of liquid–liquid extraction, solid-phase extraction and co-precipitation preconcentration methods for the determination of cadmium, copper, nickel, lead and zinc in seawater, Anal. Chim. Acta, 576 (2006) 221.

[66] X. Tang, Z. Xu, J. Wang, A hydride generation atomic fluorescence spectrometric procedure for selenium determination after flow injection on-line co-precipitate preconcentration, Spectrochim. Acta Part B 60 (2005) 1580.

[67] D. Atanassove, V. Stefanove, E. Russeva, Co-precipitative pre-concentration with sodium diethyldithiocarbamate and ICP-AES determination of Se, Cu, Pb, Zn, Fe, Co, Ni, Mn, Cr and Cd in water, Talanta 47 (1998) 1237.

[68] V.P. Bukar, Fractional Evaporation as a Method for Trace Element Preconcentration in the Analysis of Rocks and Minerals, J. Anal. Chem. 58 (2003) 657.

[69] A.J. Bard, Electroanalytical chemistry, vol. 16, Marcel Dekker, New York, 1989.

[70] G. Gillain, Studies of pretreatments in the determination of Zn, Cd, Pb, Cu, Sb and Bi in suspended particulate matter and plankton by differential-pulse anodic-stripping voltammetry with a hanging mercury drop electrode, Talanta 29 (1982) 651.

[71] H.E. Usdowski, Fraktionierung der spurenelemente bei der kristallisation, Springer-Verlag, Berlin, 1975.

55

[72] N. Hagadone, H. Zeitlin, The separation of vanadium from sea water by adsorption colloid flotation, Anal. Chim. Acta, 86 (1976) 289.

[73] M. Soylak, Y.E. Unsal, N. Kizil, A. Aydin, Utilization of membrane filtration for preconcentration and determination of Cu(II) and Pb(II) in food, water and geological samples by atomic absorption Spectrometry, Food Chem. Toxicol. 48 (2010) 517.

[74] D. Citak, M. Tuzen, A novel preconcentration procedure using cloud point extraction for determination of lead, cobalt and copper in water and food samples using flame atomic absorption spectrometry, Food Chem. Toxicol. 48 (2010) 1399.

[75] M. J. M. Wells, Essential guides to method development in solid-phase extraction, in: I. D. Wilson, E. R. Adlard, M. Cooke, and C. F. Poole (Eds), Encyclopedia of separation science, vol. 10, Academic Press, London, 2000, p 4636.

[76] J.S. Fritz, Analytical solid-phase extraction, Wiley-VCH, New York, 1999, p. 264.

[77] J.C. Whitehorn, PERMUTIT” AS A REAGENT FOR AMINES, J. Biol. Chem. 56 (1923) 751.

[78] J.C. Whitehorn, A CHEMICAL METHOD FOR ESTIMATING EPINEPHRINE IN BLOOD, J. Biol. Chem. 108 (1935) 633.

[79] A. Lund, Simultaneous Fluorimetric Determinations of Adrenaline and Noradrenaline in Blood, Acta Pharmacol. 6 (1950) 137.

[80] S. Bergstrom, G. Hansson, The use of Amberlite IRC-50 for the purification of adrenaline and histamine, Acta Physiol. Scand. 22 (1951) 87.

[81] A. Bertler, A. Carlsson, E. Rosengren, A Method for the Fluorimetric Determination of Adrenaline and Noradrenaline in Tissues, Acta Physiol. Scand. 44 (1958) 273.

[82] V.P. Dole, W.K. Kim, I. Eglitis, Detection of Narcotic Drugs, Tranquilizers, Amphetamines, and Barbiturates in Urine, JAMA 198 (1966) 349.

[83] J.M. Fujimoto, R.I.H. Wang, A method of identifying narcotic analgesics in human urine after therapeutic doses, Toxicol. App. Pharmacol. 16 (1970) 186.

[84] J.M. Meola, M. Vanko, Use of Charcoal to Concentrate Drugs from Urine before Drug Analysis, Clin. Chem. 20 (1974) 184.

[85] N. Narasimhachari, Evaluation of C18, J. Chromatogr. 225 (1981) 189.

Sep-Pak cartridges for biological sample clean-up for tricyclic antidepressant assays

[86] I. Liska, Fifty years of solid-phase extraction in wateranalysis-historical development and overview, J. Chromatogr. A 885 (2000) 3.

[87] M.C. Hennion, Sample handling strategies for the analysis of non-volatile organic compounds from environmental water samples, Trends Anal. Chem. 10 (1991) 317.

56

[88] J.L. Lundgren, A.A. Schilt, Analytical studies and applications of ferroin type chromogens immobilized by adsorption on a styrene-divinylbenzene copolymer, Anal. Chem. 49 (1977) 974.

[89] M. Chikuma, M. Nakayama, T. Itoh, H. Tanaka, K. Itoh, Chelate-forming resins prepared by modification of anion-exchange resins, Talanta 27 (1980) 807.

[90] H. Akaiwa, H. Kawamoto, K. Ogura, Kinetic studies of ion-exchange of cobalt(II) and nickel(II) on a resin loaded with 5-sulfo-8-quinolinol, Talanta 28 (1981) 337.

[91] K.S. Lee, W. Lee, D.W. Lee, Selective separation of metal ions by a chelating agent-loaded anion exchanger, Anal. Chem. 50 (1978) 255.

[92] K. Kilian, K. Pyrzynska, Preconcentration of metal ions on porphyrin-modified sorbents as pretreatment step in AAS determination, Fresenius J. Anal. Chem. 371 (2001) 1076.

[93] A.A. Atia, A.M. Donia, K.Z. Elwakeel, Selective separation of mercury (II) using a synthetic resin containing amine and mercaptan as chelating groups, React .Funct. Polym. 65 (2005) 267.

[94] M. Pesavento, R. Biesuz, M. Gallorini, A. Profumo,Sorption mechanism of trace amounts of divalent metal ions on a chelating resin containing iminodiacetate groups, Anal. Chem. 65 (1993) 2522.

[95] M. Pesavento, R. Biesuz, J.L. Cortina, Sorption of metal ions on a weak acid cation-exchange resin containing carboxylic groups, Anal. Chim. Acta 298 (1994) 225.

[96] X. Ma, Y. Li, Z. Ye, L. Yang, L. Zhou, L. Wang, Novel chelating resin with cyanoguanidine group: Useful recyclable materials for Hg(II) removal in aqueous environment, J. Hazard. Mater. 185 (2011) 1348.

[97] H. Kumagai, Y. Inoue, T. Yokoyama, T.M. Suzuki, T.Suzuki, Chromatographic selectivity of rare earth elements on iminodiacetate-type chelating resins having spacer arms of different lengths: importance of steric flexibility of functional group in a polymer chelating resin, Anal. Chem. 70 (1998) 4070.

[98] J. Seneviratne, J.A. Cox, Sol–gel materials for the solid phase extraction of metals from aqueous solution, Talanta 52 (2000) 801.

[99] M.C. Carson, Ion-pair solid-phase extraction, J. Chromatogr. A 885 (2000) 343.

[100] V. Porta, E. Mentasti, C. Sarzanini, M.C. Gennaro, Ionpair liquid–solid extraction for the preconcentration of trace metal ions, Talanta 35 (1988) 167.

[101] P. Janos, K. Stulik, V. Pacakova, An ion-exchange separation of metal cations on a C-18 column coated with dodecylsulfate, Talanta 39 (1992) 29.

[102] R. Van Grieken, Preconcentration methods for the analysis of water by X-ray spectrometric techniques, Anal. Chim. Acta 143 (1982) 3.

57

[103] A.B. Tawali, G. Schwedt, Combination of solid phase extraction and flame atomic absorption spectrometry for differentiated analysis of labile iron(II) and iron(III) species, Fresenius J. Anal. Chem. 357 (1997) 50.

[104] J.L. Gomez-Ariza, J.A. Pozas, I. Giraldez, E. Morales, Use of solid phase extraction for speciation of selenium compounds in aqueous environmental samples, Analyst 124 (1999) 75.

[105] S. Tokaliglu, S. Kartal, L. Elci, Determination of some trace elements in high purity aluminium, zinc and commercial steel by AAS after preconcentration on Amberlite XAD-1180 resin, Microchim. Acta 127 (1997) 281.

[106] M. Soylak, L. Elci, M. Dogan, Spectrophotometric determination of trace amounts of tungsten in geological samples after preconcentration on Amberlite XAD-1180, Talanta 42 (1995) 1513.

[107] S. Tokalioglu, S. Kartal, L. Elci, Determination of copper, cadmium, lead and bismuth in high purity zinc metal samples by atomic absorption spectrometry after preconcentration using Amberlite XAD-1180 resin, Anal. Sci. 10 (1994) 779.

[108] M. Soylak, L. Elci, Solid phase extraction of trace metal ions in drinking water samples from Kayseri-Turkey, J. Trace Microprobe Tech. 18 (2000) 397.

[109] A. Tunceli, A.R. Turker, Determination of gold in geological samples and anode slimes by atomic absorption spectrometry after preconcentration with Amberlite XAD-16 resin, Analyst 122 (1997) 239.

[110] A. Tunceli, A.R. Turker, Determination of palladium in alloy by flame atomic absorption spectrometry after its preconcentration if its iodocomplex on Amberlite XAD-16, Anal. Sci. 16 (2000) 81.

[111] M.A. Abdullah, L. Chiang, M. Nadeem, Comparative evaluation of adsorption kinetics and isotherms of a natural product removal by Amberlite polymeric adsorbents, Chem. Eng. J. 146 (2009) 370.

[112] L. Elci, M. Soylak, A. Uzym, E. Buyukpatir, M. Dogan, Determination of trace impurities in some nickel compounds by flame atomic absorption spectrometry after solid phase extraction using Amberlite XAD-16 resin, Fresenius J. Anal. Chem. 368 (2000) 358.

[113] E. Mentasti, V. Porta, O. Abollino, C. Sarzanini, Metal trace determinations in sea water samples from Antarctica, Anal. Chim. 81 (1991) 343.

[114] A.M. Nagmush, M. Trojanowicz, E. Olbrychleszynska, Flow injection flame atomic absorption spectrometric determination of copper with preconcentration ligand loaded Amberlite XAD-2, J. of Anal. At. Spectrom. 7 (1992) 323.

[115] S.L.C. Ferreira, H.C. Dossantos, J.R. Ferriera, N.M.L. Dearaujo, A.C.S. Costa, D.S. Dejesus, Preconcentration and determination of copper and zinc in natural water samples by ICP-AES after complexation and sorption on Amberlite XAD-2, J. Brazilian Chem. Soc. 9 (1998) 525.

58

[116] O. Abollino, M. Aceto, M.C. Bruzzoniti, E. Mentasti, C. Sarzamini, Determination of metals in highly saline matrices by solid phase extraction and slurry-sampling inductively coupled plasma atomic emission spectrometry, Anal. Chim. Acta 375 (1998) 293.

[117] P. Bermejo-Barrera, G. Gonzalez-Campos, M. Ferron-Novais, A. Bermejo-Barrera, Column preconcentration of organotin with tropolone-immobilized and their determination by electrothermal atomization absorption spectrometry, Talanta 46 (1998) 1479.

[118] S. L.C. Ferreira, C.F. Debrito, A.F. Dantas, N.M. Lopode Araujo, A.C.S. Costa, Nickel determination in saline matrices by ICP-AES after sorption on Amberlite XAD-2 loaded with PAN, Talanta 48 (1999) 1173.

[119] S.L.C. Ferreira, C.F. Debrito, Separation and preconcentration of cobalt after sorption onto Amberlite XAD-2 loaded with 2-(2-thiazolylazo)-p-cresol, Anal. Sci. 15 (1999) 189.

[120] S.L.C. Ferreira, J.R. Ferreira, A.F. Dantas, V.A. Lemos, N.M.L. Araujo, A.C.S. Costa, Copper determination in natural water samples using FAAS after preconcentration onto Amberlite XAD-2 loaded with calmagite, Talanta 50 (2000) 1253.

[121] S.L.C. Ferreira, V.A. Lemos, B.C. Moveira, A.C.S. Costa, R.E. Santelli, An on-line continuous flow system for copper enrichment and determination by flame atomic absorption spectrometry, Anal. Chim. Acta 403 (2000) 259.

[122] M. Karve, R.V. Rajgor, Amberlite XAD-2 impregnated organophosphinic acid extractant for separation of uranium(VI) from rare earth elements, Desalination 232 (2008) 191.

[123] R. Saxena, A.K. Singh, S.S. Sambi, Synthesis of a chelating polymer matrix by immobilizing alizarin red-S on Amberlite XAD-2 and its application to preconcentration of lead(II), cadmium(II), zinc(II) and nickel(II), Anal. Chim. Acta 295 (1994) 199.

[124] M. Kumar, D.P.S. Kathore, A.K. Singh, Metal ion enrichment with Amberlite XAD-2 functionalized with Tiron: analytical applications, Analyst 125 (2000) 1221.

[125] M. Kumar, D.P.S. Rathore, A.K. Singh, Pyrogallol immobilized Amberlite XAD-2: A newly designed collector for enrichment of metal ions prior to their determination by flame atomic absorption spectrometry, Microchim. Acta 137 (2001) 127.

[126] P.K. Tewari, A.K. Singh, Thiosalicylic acid-immobilized Amberlite XAD-2: Metal sorption behavior and applications in estimation of metal ions by flame atomic absorption spectrometry, Analyst 125 (2000) 2350.

[127] M. Kumar, D.P.S. Rathore, A.K. Singh, Amberlite XAD- 2 functionalized with o-aminophenol: synthesis and applications as extractant for copper(II), cobalt(II), cadmium(II), nickel(II), zinc(II) and lead(II), Talanta 51 (2000) 1187.

59

[128] P.K. Tewari, A.K. Singh, Amberlite XAD-2 functionalized with chromatropic acid: Synthesis of a new polymer matrix and its applications in metal ion enrichment for their determination by flame atomic absorption spectrometry, Analyst 124 (1999) 1847.

[129] R. Saxena, A.K. Singh, Pyrocatechol violet immobilized Amberlite XAD-2: Synthesis and metal-ion uptake properties suitable for analytical applications, Anal. Chim. Acta 340 (1997) 285.

[130] R. Saxena, A.K. Singh, D.P.S. Rathore, Salicylic acid functionalized polystyrene sorbent Amberlite XAD-2. Synthesis and applications as a preconcentrator in the determination of zinc(II) and lead(II) by using atomic absorption spectrometry, Analyst 120 (1995) 403.

[131] V.K. Jain, S.S. Sait, P.S. Shrivastav, Y.K. Agrawal, Application of chelate forming resin Amberlite XAD-2-o-vanillin vanillinthiosenicarhazone to the separation and preconcentration of copper(II), zinc(II) and lead(II), Talanta 45 (1997) 397.

[132] V.K. Jain, S.S. Sait, P. Shrivastav, Y.K. Agrawal, Sequential separation and trace enrichment of thorium(IV) and uranium(VI) on chelating resin Amberlite XAD-2-orthovanillin thiosemicarbazone (O-Vtsc), Sep. Sci. Technol. 33 (1998) 1803.

[133] M. Dogutan, H. Filik, S. Demirci, R. Apak, The use of palmitoylhydroxyquinoline functionalized Amberlite XAD-2 copolymer resin for the preconcentration and speciation analysis of gallium(III), Sep. Sci. Technol. 35 (2000) 2083.

[134] A. Suebert, G. Petzold, J.W. McLaren, Synthesis and application of an inert type of 8-hydroxyquinoline-based chelating ion exchanger for seawater analysis using on-line inductively coupled plasma mass spectrometry detection, J. Anal. At. Spectrom. 10 (1995) 371.

[135] E. Obrychsleszynska, K. Brazter, W. Matu-Zewski, M. Trojanowicz, W. Frenzel, Modification of nonionic adsorbent with eriochrome blue black R for selective nickel(II) preconcentration in conventional and flow injection atomic absorption spectrometry, Talanta 39 (1992) 779.

[136] D. Yuan, I.L. Shuttler, Flow injection column preconcentration directly coupled with electrothermal atomization atomic absorption spectrometry for the determination of aluminium. Comparison of column packing materials, Anal. Chim. Acta 316 (1995) 313.

[137] L. Elci, M. Soylak, M. Dogan, Preconcentration of trace metals in river waters by the application of chelate adsorption on Amberlite XAD-4, Fresenius J. Anal. Chem. 342 (1992) 175.

[138] M. Soylak, L. Elci, M. Dogan, Determination of some trace metals in dialysis solutions by atomic absorption spectrometry after preconcentration, Anal. Lett. 26 (1993) 1997.

[139] A.N. Masi, R.A. Olsima, Amberlite XAD copolymers loaded with 8- hydroxyquinoline and 2-(2-5-chloropyridylazo)-5-dimethylaminophenol as chelating agents for rare earth preconcentration, Ann. Chim. 89 (1993) 341.

60

[140] A.N. Masi, R.A. Olsima, Preconcentration and determination of Ce, La and Pr by X-ray fluorescence analysis using Amberlite XAD resins loaded with 8-quinolinol and 2-(2-5-chloropyridylazo)-5-dimethylamino)-phenol, Talanta 40 (1993) 931.

[141] H. Yang, K. Huang, S. Jiang, C. Wu, C. Chou, Determination of trace metal ions in water samples by on-line preconcentration and inductively coupled plasma mass spectrometry, Anal. Chim. Acta 282 (1993) 437.

[142] N. Uehra, A. Katamine, Y. Shijo, High-performance liquid chromatographic determination of cobalt(II) as the 2-(5-bromo-2-pyridylazo)-5-diethyl aminophenol chelate after preconcentration with a cation-exchange resin, Analyst 119 (1994) 1333.

[143] A.N. Masi, R.A. Olsima, Preparation and characterization of chelating resins loaded with 2-(5-bromo-2-pyridylazo)-5-(diethylamino) phenol for preconcentration of rare earth elements, Fresenius J. Anal. Chem. 357 (1997) 65.

[144] A.N. Masi, R.A. Olsima, Preparation of thin films with loaded resins for the preconcentration and determination of rare elements by X-ray fluorescence spectroscopy, X-ray Spectrom. 25 (1996) 221.

[145] A.N. Masi, R.A. Olsima, Determination by XRF of trace amounts of Ga and in geological samples preconcentrated with macroporous resins loaded with 5-phenylazo-8-quinolinol (5-phaq), J. Trace Microprobe Tech. 17 (1999) 315.

[146] M. Soylak, L. Elci, M. Dogan, Flame atomic absorption spectrometric determination of cadmium, cobalt, copper, lead and nickel in chemical grade potassium salts after an enrichment and separation procedure, J. Trace Microprobe Tech. 17 (1999) 149.

[147] Y.N. Lee, H.S. Choi, Determination of copper(II) in various samples by flame atomic absorption spectrophotometry after column preconcentration onto pulverized Amberlite XAD-4 loaded with N-benzoylphenylhydroxylamine, J. Anal. Chem. 62 (2007) 845.

[148] S.D. Cekic, H. Filik, R. Apak, Use of o-aminobenzoic acid functionalized XAD-4 copolymer resin for the separation and preconcentration of heavy metal(II) ions, Anal. Chim. Acta 505 (2003) 15.

[149] V.K. Jain, A. Handa, S.S. Sait, P. Shrivastav, Y.K. Agrawal, Preconcentration, separation and trace determination of lanthanum(III), cerium(III), thorium(IV) and uranium(VI) on polymer supported o-vanillin semicarbazone, Anal. Chim. Acta 429 (2001) 237.

[150] S. Hirata, H. Yoshihara, M. Aihara, Determination of iron(II) and total iron in environmental water samples by flow injection analysis with column preconcentration of chelating resin functionalized with N-hydroxyethylene diamine ligands and chemiluminescence detection, Talanta 49 (1997) 1059.

[151] K. Dev, G.N. Rao, Synthesis, characterization and metal sorption studies of a chelating resin functionalized with N-hydroxyethylenediamine ligands, Analyst 120 (1995) 2509.

61

[152] J. Boudenne, S. Boussetta, C. Brach-Papa, C. Branger, A. Margaillan, F. Theraulaz, Modification of poly(styrene-co-divinylbenzene) resin by grafting on an aluminium selective ligand, Poly. Int. 51 (2002) 1050.

[153] S. Yalcin, R. Apak, Chromium(III, VI) speciation analysis with preconcentration on a maleic acid-functionalized XAD sorbent, Anal. Chim. Acta 505 (2003) 25.

[154] J.M. Gladis, T.P. Rao, Quinoline-8-ol immobilized Amberlite XAD-4: synthesis, characterization and uranyl ion uptake properties suitable for analytical applications, Anal. Bioanal. Chem. 373 (2002) 867.

[155] A.R. Turker, A. Tunceli, Preconcentration of copper, nickel and zinc with Amberlite XAD-16 resin, Fresenius J. Anal. Chem. 345 (1993) 755.

[156] M. Soylak, M. Dogan, Separation and enrichment of zinc, copper, iron, cadmium, cobalt and nickel from urine with Amberlite XAD-16 resin, Trace Elem. Electrolytes 13 (1996) 130.

[157] M. Soylak, L. Elci, Preconcentration and separation of trace metal ions from seawater samples by sorption on AmberliteXAD-16 after complexation with sodium diethyl dithiocarbamate, Int. J. Environ. Anal. Chem. 66 (1997) 51.

[158] M. Soylak, V. Divrikli, M. Dogan, Column separation and enrichment of trace amounts of Cu, Ni and Fe on XAD-16 resin in industrial fertilizers after complexation with 4-(2-thiazolylazo) resorcinol, J. Trace Microprobe Tech. 15 (1997) 197.

[159] M. Soylak, L. Elci, M. Dogan, Determination of trace amounts of cobalt in natural water samples as 4-(4-thiazolylazo) resorcinol complex after adsorptive preconcentration, Anal. Lett. 30 (1997) 623.

[160] M. Merdivan, M.Z. Ouz, C. Hamamci, Sorption behaviour of uranium(VI) with N,N-dibutyl-N’-benzoylthiourea impregnated in Amberlite XAD-16, Talanta 55 (2001) 639.

[161] K. Shakir, M. Aziz, S.G. Beheir, Studies on uranium bearing phosphatic sandstone by a combined Heap leaching liquid gel extraction process 2-liquid gel extraction, Hydrometallurgy 31 (1992) 41.

[162] D. Prabhakaran, M.S. Subramanian, Selective extraction and sequential separation of actinide and transition ions using AXAD-16-BTBED polymeric sorbent, React. Funct. Polym. 57 (2003) 147.

[163] G. Venkatesh, A.K. Singh, 2-{[1-(3,4-Dihydroxyphenyl)methylidene]amino}ben-zoic acid immobilized Amberlite XAD-16 as metal extractant, Talanta 67 (2005) 187.

[164] G. Venkatesh, A.K. Singh, 4-{[(2-Hydroxyphenyl)imino]methyl}-1,2-benzene-diol (HIMB) anchored Amberlite XAD-16: Preparation and applications as metal extractants, Talanta 71 (2007) 282.

62

[165] S.Q. Memon, M.I. Bhanger, S.M. Hasany, M.Y. Khuhawar, The efficacy of nitrosonaphthol functionalized XAD-16 resin for the preconcentration/sorption of Ni(II) and Cu(II) ions, Talanta 72 (2007) 1738.

[166] D. Prabhakaran, M.S. Subramanian, A new chelating sorbent for metal ion extraction under high saline conditions, Talanta 59 (2003) 1227.

[167] M.E. Mahmoud, M.M. Osman, M.E. Amer, Selective pre-concentration and solid phase extraction of mercury( II) from natural water by silica gel-loaded dithizone phases, Anal. Chim. Acta 415 (2000) 33.

[168] M.E. Mahmoud, G.A. Gohar, Silica gel-immobilizeddithioacetal derivatives as potential solid phase extractors for mercury(II), Talanta 51 (2000) 77.

[169] Z. Tu, Z. Hu, X. Chang, L. Zhang, Q. He, J. Shi, R. Gao, Silica gel modified with 1-(2-aminoethyl)-3-phenylurea for selective solid-phase extraction and preconcentration of Sc(III) from environmental samples, Talanta 80 (2010) 1205.

[170] M.E. Mahmoud, M.S.M. Al Saadi, Selective solid phase extraction and preconcentration of iron(III) based on silica gel-chemically immobilized purpurogallin, Anal.Chim. Acta 450 (2001) 239.

[171] K.S. Abou-El-Sherbini, I.M.M. Kenawy, M.A. Hamed, R.M. Issa, R. Elmorsi, Separation and preconcentration in a batch mode of Cd(II), Cr(III, VI), Cu(II), Mn(II,VII) and Pb(II) by solid-phase extraction by using of silica modified with N-propylsalicylaldimine, Talanta 58 (2002) 289.

[172] R. Garcia-Valls, A. Hrdlicka, J. Perutka, J. Havel, N.V. Deorkard, L.L. Tavlarides, M. Munoz, M. Valiente, Separation of rare earth elements by high performance liquid chromatography using a covalent modified silica gel column, Anal. Chim. Acta 439 (2001) 247.

[173] J. Saurina, C. Leal, R. Compano, M. Granados, R. Tauler, M.D. Prat, Determination of triphenyltin in seawater by excitation–emission matrix fluorescence and multivariate curve resolution, Anal. Chim. Acta 409 (2000) 237.

[174] M. Akhond, G. Absalan, L. Sheikhian, M.M. Eskandari, H. Sharghi, Di (n-propyl) thiuram disulfide bonded on silica gel as a new sorbent for separation, preconcentration, and measurement of silver ion from aqueous samples, Separ. Sci. Technol. 52 (2006) 53.

[175] M. Shamsipur, F. Raoufi, H. Sharghi, Solid phase extraction and determination of lead in soil and water samples using octadecyl silica membrane disks modified by biswl-hydroxy-9,10-anthraquinone-2-methylxsulphide and flame atomic absorption spectrometry, Talanta 52 (2000) 637.

[176] G. Philippeit, J. Angerer, Determination of palladium in human urine by high-performance liquid chromatography and ultraviolet detection after ultraviolet photolysis and selective solid-phase extraction, J. Chromatogr. B 760 (2001) 237.

[177] W. Ngeontae, W. Aeungmaitrepirom, T. Tuntulani, Chemically modified silica gel with aminothioamidoanthraquinone for solid phase extraction and

63

preconcentration of Pb(II), Cu(II), Ni(II), Co(II) and Cd(II), Talanta 71( 2007) 1075.

[178] M.H. Pournaghi-Azar, Dj. Djozan, H.A. Zadeh, Determination of trace bismuth by solid phase extraction and anodic stripping voltammetry in non-aqueous media, Anal. Chim. Acta 437 (2001) 217.

[179] E. Vassileva, K. Hadjiinov, T. Stoychev, C. Daiev, Chromium speciation analysis by solid-phase extraction on a high surface area TiO2

[180] S.J. Kumar, P. Ostapczuk, H. Emons, Chromium speciation in water by electrothermal AAS after simultaneous adsorption of Cr(III) and Cr(VI) on activated alumina mini column, At. Spectrosc. 20 (1999) 194.

, Analyst 125 (2000) 693.

[181] A.C. Sahayam, Speciation of Cr(III) and Cr(VI) in potable waters by using activated neutral alumina as collector and ET-AAS for determination, Anal. Bioanal. Chem. 372 (2002) 840.

[182] P. Liang, Y. Qin, B. Hu, C. Li, T. Peng, Z. Jiang, Study on the adsorption behavior of heavy metal ions on nanometer-size titanium dioxide with ICP–AES, Fresenius J. Anal. Chem. 368 (2000) 638.

[183] C.W. Huck, G.K. Bonn, Recent developments in polymer-based sorbents for solid-phase extraction, J. Chromatogr. A 885 (2000) 51.

[184] E. Gonzalez-Toledo, M. Benzi, R. Compano, M. Granados, M.D. Prat, Speciation of organotin compounds in shellfish by liquid chromatography-fluorimetric detection, Anal. Chim. Acta 443 (2001) 183.

[185] R. Compano, R. Ferrer, J. Guiteras, M.D. Prat, Spectrofluorimetric detection of zinc and cadmium with 8-(benzene sulfonamido)-quinoline immobilized on a polymeric matrix, Analyst 119 (1994) 1225.

[186] P.K. Tewari, A.K. Singh, Preconcentration of lead with Amberlite XAD-2 and Amberlite XAD-7 based chelating resins for its determination by flame atomic absorption spectrometry, Talanta 56 (2002) 735.

[187] P.K. Tewari, A.K. Singh, Amberlite XAD-7 impregnated with xylenol orange; a chelating collector for preconcentration of Cd(II), Co(II), Cu(II), Ni(II), Zn(II) and Fe(III) ions prior to their determination by flame AAS, Fresenius J. Anal. Chem. 367 (2000) 562.

[188] C.S.L. Ferreira, D.S. Jesus, R.J. Cassella, A.C.S. Costa, M.S. Carvalho, R.E. Santelli, An on-line solid phase extraction system using polyurethane foam for the spectrophotometric determination of nickel in silicates and alloys, Anal. Chim. Acta 378 (1999) 287.

[189] S.M. Abdel Azeem, W.A.A. Arafa, M.F. El-Shahat, Synthesis and application of alizarin complexone functionalized polyurethane foam: Preconcentration/separation of metal ions from tap water and human urine, J. Hazard. Mater. 182 (2010) 286.

64

[190] E.M. Gama, A. da S. Lima, V.A. Lemos, Preconcentration system for cadmium and lead determination in environmental samples using polyurethane foam/Me-BTANC, J. Hazard. Mater. 136 (2006) 757.

[191] S.P. Quinaia, J.B.B. Da Silva, M.C.E. Rollemberg, A.J. Curtius, Preconcentration of lead complexed with O,O-diethyl-dithiophosphate by column solid-phase extraction using different sorbents in a flow injection system coupled to a flame atomic absorption spectrometer, Talanta 54 (2001) 687.

[192] I.A. Veselova, T.N. Shekhovtsova, Visual determination of lead(II) by inhibition of alkaline phosphatase immobilized on polyurethane foam, Anal. Chim. Acta 413 (2000) 95.

[193] A.N. Anthemidis, G.A. Zachariadis, J.A. Stratis, Online solid phase extraction system using PTFE packed column for the flame atomic absorption spectrometric determination of copper in water samples, Talanta 54 (2001) 935.

[194] A.N. Anthemidis, G.A. Zachariadis, J.S. Kougoulis, J.A. Stratis, Flame atomic absorption spectrometric determination of chromium(VI) by on-line preconcentration system using a PTFE packed column, Talanta 57 (2002) 15.

[195] G.A. Zachariadis, A.N. Anthemidis, P.G. Bettas, J.A. Stratis, Determination of lead by on-line solid phase extraction using a PTFE micro-column and flame atomic absorption spectrometry, Talanta 57 (2002) 919.

[196] S. Tsakovski, K. Benkhedda, E. Ivanova, F.C. Adams, Comparative study of 8-hydroxyquinoline derivatives as chelating reagents for flow-injection preconcentration of cobalt in a knotted reactor, Anal. Chim. Acta 453 (2002) 143.

[197] I.E. De Vito, R.A. Olsina, A.N. Masi, Enrichment method for trace amounts of rare earth elements using chemofiltration and XRF determination, Fresenius J. Anal. Chem. 368 (2000) 392.

[198] M. Pesavento, R. Biesuz, Sorption of divalent metal ions on an iminodiacetic resin from artificial seawater, Anal. Chim. Acta 346 (1997) 381.

[199] P. Hashemi, A. Olin, Equilibrium and kinetic properties of a fast iminodiacetate based chelating ion exchanger and its incorporation in a FIA-ICP–AES system, Talanta 44 (1997) 1037.

[200] O. Abollino, M. Aceto, M.C. Bruzzoniti, E. Mentasti, C. Sarzanini, Speciation of copper and manganese in milk by solid-phase extraction by inductively coupled plasma-atomic emission spectrometry, Anal. Chim. Acta 375 (1998) 299.

[201] C. Gueguen, C. Belin, B.A. Thomas, F. Monna, P.Y. Favarger, J. Dominik, The effect of freshwater UV irradiation prior to resin preconcentration of trace metals, Anal. Chim. Acta 386 (1999) 155.

[202] H. Kumagai, T. Yokoyama, T.M. Suzuki, T. Suzuki, Liquid chromatographic selectivity and retention behavior of rare-earth elements on a chelating resin having a propylenediaminetetraacetate type functional group, Analyst 124 (1999) 1595.

65

[203] B. Gong, Y. Wang, ICP–AES determination of traces of noble metal ions pre-concentrated and separated on a new polyacrylacylaminothiourea chelating fiber, Anal. Bioanal. Chem. 372 (2002) 597.

[204] B. Wen, X.Q. Shuan, R.X. Liu, H.X. Tang, Preconcentration of trace elements in sea water with poly(acrylaminophosphonicdithiocarbamate) chelating fiber for their determination by inductively coupled plasma mass spectrometry, Fresenius J. Anal. Chem. 363 (1999) 251.

[205] B. Wen, X.Q. Shuan, J. Lian, Separation of Cr(III) and Cr(VI) in river and reservoir water with 8-hydroxyquinoline immobilized polyacrylonitrile fiber for determination by inductively coupled plasma mass spectrometry, Talanta 56 (2002) 681.

[206] B. Wen, X.Q. Shuan, S.G. Xu, Preconcentration of ultratrace rare earth elements in seawater with 8-hydroxyquinoline immobilized polyacrylonitrile hollow fiber membrane for determination by inductively coupled plasma mass spectrometry, Analyst 124 (1999) 621.

[207] M.R. Buchmeiser, R. Tessadri, G. Seeber, G.K. Bonn, Selective extraction of rare-earth elements from rocks using a high-capacity cis-1,4-butanedioic acid-functionalized resin, Anal. Chem. 70 (1998) 2130.

[208] F. Sinner, M.R. Buchmeiser, R. Tessadri, M. Mupa, K. Wurst, G.K. Bonn, Dipyridyl amide-functionalized polymers prepared by ring-opening-metathesis polymerization (ROMP) for the selective extraction of mercury and palladium, J. Am. Chem. Soc. 120 (1998) 2790.

[209] A. Afkhami, T. Madrakian, Kinetic-spectrophotometric determination of selenium in natural water after preconcentration of elemental selenium on activated carbon, Talanta 58 (2002) 311.[209]

[210] Q. He, Z. Hu, Y. Jiang, X. Chang, Z. Tu, L. Zhang, Preconcentration of Cu(II), Fe(III) and Pb(II) with 2-((2-minoethylamino)methyl)phenol-functionalized activated carbon followed by ICP-OES determination, J. Hazard. Mater. 175 (2010) 710.

[211] M. Soylak, I. Narin, L. Elci, M. Dogan, Atomic absorption-spectrometric determination of copper, cadmium, lead and nickel in urine samples after enrichment and separation procedure on an activated carbon column, Trace Elem. Electrolytes 16 (1999) 131.

[212] Y. Zhao, C. Liu, M. Feng, Z. Chen, S. Li, G. Tian, L. Wang, J. Huang, S. Li, Solid phase extraction of uranium(VI) onto benzoylthiourea-anchored activated carbon, J. Hazard. Mater. 176l (2010) 119.

[213] M. Ghaedi, A. Shokrollahi, A.H. Kianfar, A.Pourfarokhi, N. Khanjari, A.S. Mirsadeghi, M. Soylak, Preconcentration and separation of trace amount of heavy metal ions on bis(2-hydroxy acetophenone)ethylendiimine loaded on activated carbon, J. Hazard. Mater.162 (2009) 1408.

66

[214] L. Zhang, X. Chang, Z. Li, Q. He, Selective solid-phase extraction using oxidized activated carbon modified with triethylenetetramine for preconcentration of metal ions, J. Mol. Struct. 964 (2010) 58.

[215] Yeuk-Ki Tsoi, K. Sze-Yin Leung, Toward the use of surface modified activated carbon in speciation: Selective preconcentration of selenite and selenate in environmental waters, J. Chromatogr. 1218 (2011) 2160.

[216] K. Zih-Perenyi, A. Lasztity, S. Pusztai, Study of interference of pharmaceuticals with complexing characteristics in solid phase microextraction of lead on chelating celluloses, Microchem. J. 85 (2007) 149.

[217] M. Chen, T. Yang, J. Wang, Precipitate coating on cellulose fibre as sorption medium for selenium preconcentration and speciation with hydride generation atomic fluorescence spectrometry, Anal. Chim. Acta 631 (2009) 74.

[218] N. Rajesh, M.S. Hari, Spectrophotometric determination of inorganic mercury (II) after preconcentration of its diphenylthiocarbazone complex on a cellulose column, Spectrochim. Acta Part A 70 (2008) 1104.

[219] A. Bhalotra, B.K. Puri, Preconcentration of bismuth(III) and copper(II) by solid-phase extraction and subsequent determination by differential pulse polarography, J. AOAC Intern. 84 (2001) 47.

[220] N. Pourreza, R. Hoveizavi, Simultaneous preconcentration of Cu, Fe and Pb as methylthymol blue complexes on naphthalene adsorbent and flame atomic absorption determination, Anal. Chim. Acta 549 (2005) 124.

[221] B.K. Puri, S. Balani, Preconcentration of iron(III), cobalt(II) and copper(II) nitroso-R-complexes on tetradecyldimehtylbenzylammonium iodide-naphthalene adsorbent, Talanta 42 (1995) 337.

[222] B.K. Puri, K.W. Jackson, M. Katyal, Analytical applications of the technique of solid-liquid separation after liquid-liquid extraction, Microchem. J. 36 (1987) 135.

[223] A.P. dos Anjos, L. Cornejo-Ponce, S. Cadore, N. Baccan, Determination of manganese by flame atomic absorption spectrometry after its adsorption onto naphthalene modified with 1-(2-pyridylazo)-2-naphthol (PAN), Talanta 71 (2007) 1252.

[224] M. Satake, T. Nagahiro, B.K. Puri, Column preconcentration of cobalt in alloys and pepperbush using 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol and ammonium tetraphenylborate adsorbent supported on naphthalene with subsequent determination using atomic absorption spectrometry, Analyst 118 (1993) 85.

[225] S. Balani, B.K. Puri, Column chromatographic preconcentration of palladium in alloys with 9, 10 phenanthrenequinonemonoxime-naphthalene, Talanta 39 (1992) 815.

[226] M. Satake, T. Nagahiro, B.K. Puri, Column preconcentration of titanium in aluminium and zinc alloys with oxalic acid-ascorbic acid and the ion-pair of sodium 1,2-dihydroxybenzene-3,5-disulphonic acid and tetradecyldimethyl

67

benzylammonium chloride supported on naphthalene using spectrometry, Talanta 39 (1992) 1349.

[227] S. Walas, A. Tobiasz, M. Gawin, B. Trzewik, M. Strojny, H. Mrowiec, Application of a metal ion-imprinted polymer based on salen–Cu complex to flow injection preconcentration and FAAS determination of copper, Talanta, 76 (2008) 96.

[228] S.J. Ahmadi, O. Noori-Kalkhoran, S. Shirvani-Arani, Synthesis and characterization of new ion-imprinted polymer for separation and preconcentration of uranyl (UO2

2+ J. Hazard. Mater. 175 (2010) 193.

) ions,

[229] T.P. Rao, P. Metilda, J.M. Gladis, Preconcentration techniques for uranium(VI) and thorium(IV) prior to analytical determination-an overview, Talanta 68 (2006) 1047.

[230] T.R. Krishnan, I. Ibraham, Solid-phase extraction technique for the analysis of biological samples, J. Pharm. Biomed. Anal. 12 (1994) 287.

[231] A. Mizuike, Enrichment Techniques for Inorganic Trace Analysis, Springer, Berlin, 1983.

[232] R.E. Majors, Sample preparation for HPLC and gas chromatography using solid-phase extraction, LG-GC 4 (1989) 972.

[233] T.M. Florence, G.E. Batley, Trace metals species in seawater- I. Removal of trace metals from sea-water by a chelating resin, Talanta 23 (1976) 179.

[234] M.C. Yebra, N. Carro, M.F. Enriquez, A. Moreno-Cid, A. Garcia, Field sample pre-concentration of copper in sea water using chelating minicolumns subsequently incorporated on a flow-injection-flame atomic absorption spectrometry system, Analyst 126 (2001) 933.

[235] D. M. Sanchez, R. Martin, R. Morante, J. Marin, M.L. Munuera, Preconcentration speciation method for mercury compounds in water samples using solid phase extraction followed by reversed phase high performance liquid chromatography, Talanta 52 (2000) 671.

[236] E. Castillo, J.-L. Cortina, J.-L. Beltran, M.-D. Prat, M. Granados, Simultaneous determination of Cd(II), Cu(II) and Pb(II) in surface waters by solid phase extraction and flow injection analysis with Spectrophotometric detection, Analyst 126 (2001) 1149.

[237] M. Shamsipur, A.R. Ghiasvand, H. Sharghi, H. Naeimi, Solid phase extraction of ultra trace copper(II) using octadecyl silica membrane disks modified by a naphthol- derivative Schiff’s base, Anal. Chim. Acta 408 (2000) 271.

[238] M.E. Mahmoud, E.M. Soliman, Silica-immobilized formylsalicylic acid as a selective phase for the extraction of iron(III), Talanta 44 (1997) 15.

68

[239] C.S.L. Ferreira, H.C. Santos, D.S. Jesus, Molybdenum determination in iron matrices by ICP–AES after separation and preconcentration using polyurethane foam, Fresenius J. Anal. Chem. 369 (2001) 187.

[240] J.F. Tyson, Flow injection atomic spectrometry, Spectrochim. Acta Rev. 14 (1991) 169.

[241] Y. Li, Yan-Feng Huang, Y. Jiang, Bo-lin Tian, F. Han, Xiu-Ping Yan, Displacement solid-phase extraction on mercapto-functionalized magnetite microspheres for inductively coupled plasma mass spectrometric determination of trace noble metals, Anal. Chim. Acta 692 (2011) 42.

[242] R. Kalvoda, M. Kopanica, Adsorptive Stripping Voltammetry In Trace Analysis, Pure & Appl. Chem. 61 (1989) 97.

[243] M.A. Taher, E. Rezaeipour, D. Afzali, Anodic stripping voltammetric determination of bismuth after solid-phase extraction using amberlite XAD-2 resin modified with 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol, Talanta 63 (2004) 797.

[244] D. Afzali, A. Mostafavl, M.A. Taher, E. Rezaeipour, M.K. Mahani, Natural Analcime Zeolite Modified with 5-Br-PADAP for the Preconcentration and Anodic Stripping Voltametric Determination of Trace Amount of Cadmium, Anal. Sci. 21 (2005) 383.

[245] W. Abe, S. Isaka, Y. Koike, K. Nakano, K. Fujita, T. Nakamura, X-ray fluorescence analysis of trace metals in environmental water using preconcentration with an iminodiacetate extraction disk, X-Ray Spectrom. 35 (2006) 184.

[246] H. Barros, Lué-Merú M. Parra, L. Bennun, E.D. Greaves, Determination of arsenic in water samples by Total Reflection X-Ray Fluorescence using pre-concentration with alumina, Spectrochim. Acta Part B 65 ( 2010) 489.

[247] A.A. Menegário, D.C. Pellegrinotti, M.F. Giné, V.F. N. Filho, On-line preconcentration flow system for multi-elemental analysis by total reflection X-ray fluorescence spectrometry, Spectrochimica Acta Part B 58 (2003) 543.

[248] C. Sivani , G.R. Naidu , J. Narasimhulu , D. Rekha , J.D. Kumar , P. Chiranjeevi, Determination of Co(II) in water and soil samples using spectrophotometry coupled with preconcentration on 4-amino methyl pyridine anchored silica gel column, J Hazard Mater. 146 (2007) 137.

[249] M. Soylak, Y.E. Unsal, M. Tuzen, Spectrophotometric determination of trace levels of allura red in water samples after separation and preconcentration, Food Chem. Toxicol. 49 (2011) 1183.

[250] P. Liang, J. Yang Cloud point extraction preconcentration and spectrophotometric determination of copper in food and water samples using amino acid as the complexing agent , J Food Compos Anal. 23 (2010) 95.

69

[251] P.R. Devi, T. Gangaiah, G.R.K. Naidu, Determination of trace metals in water by neutron activation analysis after preconcentration on a poly(acrylamidoxime) resin, Anal. Chim. Acta 249 (1991) 533.

[252] R.R. Rao, A. Chatt, Preconcentration neutron activation analysis of trace elements in seawater by coprecipitation with 1-(2-thiazolylazo)-2-naphthol, pyrrolidinedithio carbamate and N-nitroso-phenylhydroxylamine, J. Radioanal. Nucl. Chem. 168 (1993) 439.

[253] M. Nomura, M. Sato, H. Amakawa, Y. Oura, M. Ebihara, Precise determination of Sc in natural waters by neutron activation analysis coupled with preconcentration of Sc, Anal. Chim. Acta 553 (2005) 58.

[254] T. Asadollahi, S. Dadfarnia, A.M.H. Shabani, Separation/preconcentration and determination of vanadium with dispersive liquid–liquid microextraction based on solidification of floating organic drop (DLLME-SFO) and electrothermal atomic absorption spectrometry, Talanta 82 (2010) 208.

[255] J. Sardans, F. Montes, J. Penuelas, Determination of As, Cd, Cu, Hg and Pb in biological samples by modern electrothermal atomic absorption spectrometry, Spectrochim. Acta Part B 65 (2010) 97.

[256] M.T. Naseri, M.R.M. Hosseini, Y. Assadi, A. Kiani, Rapid determination of lead in water samples by dispersive liquid–liquid microextraction coupled with electrothermal atomic absorption spectrometry, Talanta 75 (2008) 56.

[257] A. Montaser, D.W. Golightly, Inductively Coupled Plasmas in Analytical Atomic Spectrometry, second ed., VCH, New York, 1992.

[258] R.E.S. Froes, W.B. Neto, R.L.P. Naveira , N.C. Silva , C.C. Nascentes, J.B.B. da Silva, Exploratory analysis and inductively coupled plasma optical emission spectrometry (ICP-OES) applied in the determination of metals in soft drinks, Microchem. J. 92 (2009) 68.

[259] L.A. Escudero, L.D. Martinez, J.A. Salonia, J.A. Gasquez, Determination of Zn(II) in natural waters by ICP-OES with on-line preconcentration using a simple solid phase extraction system, Microchem. J. 95 (2010) 164.

[260] Tsung-Ting Shih, Wei-Yu Chen, Yuh-Chang Sun, Open-channel chip-based solid-phase extraction combined with inductively coupled plasma-mass spectrometry for online determination of trace elements in volume-limited saline samples, J. Chromatogr. A, 1218 (2011) 2342.

[261] F.A. Aydin, M. Soylak, Separation, preconcentration and inductively coupled plasma-mass spectrometric (ICP-MS) determination of thorium(IV), titanium(IV), iron(III), lead(II) and chromium(III) on 2-nitroso-1-naphthol impregnated MCI GEL CHP20P resin, J. Hazard. Mater. 173 (2010) 669.

[262] S. Baytaka, F. Zereenb, Z. Arslanb, Preconcentration of trace elements from water samples on a minicolumn of yeast (Yamadazyma spartinae) immobilized TiO2 nanoparticles for determination by ICP-AES, Talanta 84 (2011) 319.

70

[263] B. Debelius, J.M. Forja, A.D. Valls, L.M. Lubian, Toxicity and bioaccumulation of copper and lead in five marine microalgae, Ecotoxicol. Environ. Saf. 72 (2009) 1503.

[264] M.B. Sperling, B. Welz, Atomic Absorption Spectrometry, Wiley-VCH, Weinheim, 1999.

[265] B.V. Lvov, Fifty years of atomic absorption spectrometry, J. Anal. Chem. 60 (2005) 382.

[266] S. Tokahoglu, H. Ayhanoz, Use of Cu(II) and Fe(III) N-benzoyl-N-phenylhydroxylamine coprecipitants for preconcentration of some trace metal ions in food samples, Food Chemistry 127 (2011) 359.

[267] C.T.J. Alkemade, T. Hollander, W. Snelleman, P.J.T. Zeegers, Metal Vapours in Flames, Pergamon Press, Oxford, 1982.

[268] B.V. Lvov, Forty years of electrothermal atomic absorption spectrometry. Advances and problems in theory, Spectrochim. Acta B 52 (1997) 1239.

[269] J.A.C. Broekaert, Analytical Atomic Spectrometry with Flames and Plasmas, 3rd

[270] D.A. Skoog, F.J. Holler, S.A. Crouch, Instrumental analysis, India edn., Books/Cole- a part of Cengage Learning, New Delhi, 2007.

edn, Wiley-VCH, Weinheim, Germany, 1998.

[271] O. Axner, Laser Spectrometric Techniques in Analytical Atomic Spectrometry. In: Meyers RA ed. Encyclopedia of Analytical Chemistry, New York, John Wiley & Sons, Inc., 2000, p. 9506.

[272] A. Zybin, J. Koch, H.D. Wizemann, J. Franzke, K. Niemax, Diode laser atomic absorption spectrometry, Spectrochim. Acta B 60 (2005) 1.

[273] S.B. Smith, Jr, G.M. Hieftje, A New Background-correction Method for Atomic Absorption Spectrometry, Appl. Spectrosc. 37 (1983) 419.

[274] K. Cammann, Analytical chemistry-today's definition and interpretation, Fresenius J. Anal. Chem. 343 (1992) 812.

[275] G. M. Hieftje, The two sides of analytical chemistry, Anal. Chem. 57 (1985) 256A.

[276] D.A. Skoog, D.M. West, F.J. Holler, Fundamentals of analytical chemistry, 5th

[277] G.D. Christian, Analytical chemistry, John Wiley and Sons, 6

edn, Harcourt Asia Pte Ltd., Singapore, 2001.

th

[278] D.C Harris, Quantitative chemical analysis, 4

edn, 2003.

th

[279] J. Mandal, R.D. Stiehler, Sensitivity-A Criterion for the Composition of Methods of Test, J. Res. Narl. Bur. Std. 53 (1954) 155.

edn, W.H. Freeman and company, New York, 1995.

71

[280] Anon, Nomenclature, symbols, units and their usage in spectrochemical analysis II, Spectrochim. Acta, 33B (1978) 242.

[281] Analytical Method Committee, Recommendation for the definition, estimation and use of the detection limit, Analyst 112 (1987) 199.

[282] J.D. Ingle Jr., Sensitivity and Limit of Detection in Quantiative Spectrometric Methods, J. Chem. Educ. 51 (1974) 100.

[283] G.L. Long, J.D. Winefordner, Limit of Detection. A Closure Look at the IUPAC Definition, Anal. Chem. 55 (1983) 712A.

[284] Y. Yamini, N. Alizadeh, M. Shamsipur, Solid phase extraction and determination of ultra trace amounts of mercury(II) using octadecyl silica membrane disks modified by hexathia-18-crown-6-tetraone and cold vapour atomic absorption spectrometry, Anal. Chim. Acta 355 (1997) 69.

[285] Y. Tian, P. Yin, R. Qu, C. Wang, H. Zheng, Z. Yu, Removal of transition metal ions from aqueous solutions by adsorption using a novel hybrid material silica gel chemically modified by triethylenetetraminomethylenephosphonic acid, Chem. Eng. J. 162 (2010) 573.

[286] A. Islam, M.A. Laskar, A. Ahmad, Characterization and Application of 1-(2-Pyridylazo)-2-naphthol Functionalized Amberlite XAD-4 for Preconcentration of Trace Metal Ions in Real Matrices, J. Chem. Eng. Data 55 (2010) 5553.

[287] R. Compano, M. Granados, C. Leal, M.D. Prat, Solid phase extraction and spectrofluorimetric determination of triphenyltin in environmental samples, Anal. Chim. Acta 283 (1993) 272.

[288] Y. Yamini, J. Hassan, R. Mohandesi, N. Bahramifar, Preconcentration of trace amounts of beryllium in water sample on octadecyl silica cartridges modified by quinalizarine and its determination with atomic absorption spectrometry, Talanta 56 (2002) 375.

[289] M. Shamsipur, A.R. Ghiasvand, H. Sharghi, H. Naeimi, Solid phase extraction of ultra trace copper(II) using octadecyl silica membrane disks modified by a naphthol- derivative Schiff’s base, Anal. Chim. Acta 408 (2000) 271. [289]

[290] M. Shamsipur, M.H. Mashhadizadeh, Preconcentration of trace amounts of silver ion in aqueous samples on octadecyl silica membrane disks modified with hexathia- 18-crown-6 and its determination by atomic absorption spectrometry, Fresenius J. Anal. Chem. 367 (2000) 246.

[291] M. Shamsipur, A. Avanes, M.K. Rofouei, H. Sharghi, G. Aghapour, Solid-phase extraction and determination of ultra trace amounts of copper(II) using octadecyl silica membrane disks modified by 11-hydroxynaphthacene-5,12-quinone and flame atomic absorption spectrometry, Talanta 54 (2001) 863.

[292] C.F. Poole, A.D. Gunatilleka, R. Sethuraman, Contributions of theory to method development in solid-phase extraction, J. Chromatogr. A 885 (2000) 17.

72

[293] E.M. Thurman, K. Snavely, Advances in solid-phase extraction disks for environmental chemistry, Trends Anal. Chem. 19 (2000) 18.

[294] F. Helfferich, Ion Exchange, McGraw Hill, New York, 1962, p. 424.

[295] M. Pesavento, E. Baldini, Study of sorption of copper(II) on complexing resin columns by solid phase extraction, Anal. Chim. Acta 389 (1999) 59.

[296] K. Hirose, Y. Dokiya, Y. Sugimura, Determination of conditional stability constants of organic copper and zinc complexes dissolved in seawater using ligand exchange method with EDTA, Mar. Chem. 11 (1982) 343.

[297] P.J.M. Buckley, C.M.G.V. Berg, Copper complexation profiles in the Atlantic Ocean. A comparative study using electrochemical and ion exchange techniques, Mar. Chem. 19 (1986) 281.

[298] S.E. Manahan, Humic substances and the fates of hazardous waste chemicals, Chapter 6 in Influence of aquatic humic substances on fate and treatment of pollutants, Advances in Chemistry series 219, American Chemical Society, Washington, DC, 1989, p. 83.

[299] D.W. King, J. Lin, D.R. Kester, Spectrophotometric determination of iron(II) in seawater at nanomolar concentrations, Anal. Chim. Acta 247 (1991) 125.

[300] A. Afkhami, T. Madrakian, A.A. Assl, A.A. Sehhat, Solid phase extraction flame atomic absorption spectrometric determination of ultra-trace beryllium, Anal. Chim. Acta 437 (2001) 17.

[301] Y. Sakai, N. Mori, Preconcentration of cobalt with N-(dithiocarboxy) sarcosine and Amberlite XAD-4 resin, Talanta 33 (1986) 161.

[302] B.N. Singh, B. Maiti, Separation and preconcentration of U(VI) on XAD-4 modified with 8-hydroxy quinoline, Talanta 69 (2006) 393.

[303] S.D. Çekiç, H. Filik., R. Apak, Use of an o-aminobenzoic acid-functionalized XAD-4 copolymer resin for the separation and preconcentration of heavy metal(II) ions, Anal. Chim. Acta, 505 (2004) 15.

[304] A. Hemasundaram, N. Krishnaiah, N.V.S. Naidu, B. Sreedhar, Synthesis of 2,3-dihydroxynaphthalene-functionalized Amberlite XAD-4 resin: Applications for the separation and preconcentration of trace metal ions prior to their determination by inductively coupled plasma atomic emission spectrometry, Toxicol. Environ. Chem. 91 (2009) 1429.

[305] A. Ramesh, K.R. Mohan, K. Seshaiah, Preconcentration of trace metals on Amberlite XAD-4 resin coated with dithiocarbamates and determination by inductively coupled plasma-atomic emission spectrometry in saline matrices, Talanta 57 (2002) 243.

[306] Y. Liu, Y. Guo, X. Chang, S. Meng, D. Yang, B. Din, Column solid-phase extraction with 2-Acetylmercaptophenyldi-azoaminoazobenzene (AMPDAA) impregnated Amberlite XAD-4 and determination of trace heavy metals in natural waters by flame atomic absorption spectrometry, Microchim. Acta 149 (2005) 95.

73

[307] Y. Liu, Y. Guo, S. Meng, X. Chang, Online separation and preconcentration of trace heavy metals with 2,6-dihydroxyphenyl-diazoaminoazobenzene impregnated Amberlite XAD-4, Microchim. Acta 158 (2007) 239.

[308] A. Uzun, M. Soylak, L. Elci, Preconcentration and separation with Amberlite XAD-4 resin; determination of Cu, Fe, Pb, Ni, Cd and Bi at trace levels in waste water samples by flame atomic absorption spectrometry, Talanta 54 (2001) 197.

[309] R. Pathak, G.N. Rao, Preparation and analytical properties of a chelating resin functionalized with 1-hydrazinophthalazine ligand, Talanta 44 (1997) 1447.

[310] M. Tuzen, I. Narin, M. Soylak, L. Elci, XAD-4/PAN solid phase extraction system for atomic absorption spectrometric determinations of some trace metals in environmental samples, Anal. Lett. 37 (2005) 473.

[311] Y.S. Kim, G. In, C.W. Han, J.M. Choi, Studies on synthesis and application of XAD-4-salen chelate resin for separation and determination of trace elements by solid phase extraction, Microchem. J. 80 (2005) 151.

[312] P. Metilda, K. Sanghamitra, J.M. Gladis, G.R.K. Naidu, T.P. Rao, Amberlite XAD-4 functionalized with succinic acid for the solid phase extractive preconcentration and separation of uranium(VI), Talanta 65 (2005) 192.

[313] D. Kara, A. Fisher, S.J. Hill, Determination of trace heavy metals in soil and sediments by atomic spectrometry following preconcentration with Schiff bases on Amberlite XAD-4, J. Hazard. Mater. 165 (2009) 1165.

[314] E.J. Santos, A.B. Herrmann, A.S. Ribeiro, A.J. Curtius, Determination of Cd in biological samples by flame AAS following on-line preconcentration by complexation with O,O-diethyldithiophosphate and solid phase extraction with Amberlite XAD-4, Talanta 65 (2005) 593.

[315] H.A. Panahi, H.S. Kalal, E. Moniri, M.N. Nezhati, M.T. Menderjani, S.R. Kelahrodi, F. Mahmoudi, Amberlite XAD-4 functionalized with m-phenylendiamine: Synthesis, characterization and applications as extractant for preconcentration and determination of rhodium (III) in water samples by inductive couple plasma atomic emission spectroscopy (ICP-AES), Microchem. J. 93 (2009) 49.

[316] G. Depecker, C. Branger, A. Margaillan, T. Pigot, S. Blanc, F.R. Peillard, B. Coulomb, J.L. Boudenne, Synthesis and applications of XAD-4-DAN chelate resin for the separation and determination of Se(IV), React. Funct. Polym. 69 (2009) 877.

[317] V.A. Lemos, C.G. Novaes, A.S. Lima, D.R. Vieira, Flow injection preconcentration system using a new functionalized resin for determination of cadmium and nickel in tobacco samples, J. Hazard. Mater. 155 (2008) 128.

[318] E.V. Oral, I. Dolak, H. Temel, B. Ziyadanogullari, Preconcentration and determination of copper and cadmium ions with 1,6-bis(2-carboxy aldehyde phenoxy)butane functionalized Amberlite XAD-16 by flame atomic absorption spectrometry, J. Hazard. Mater. 186 (2011) 724.

74

[319] M. Ghaedi, K. Niknam, K. Taheri, H. Hossainian, M. Soylak, Flame atomic absorption spectrometric determination of copper, zinc and manganese after solid-phase extraction using 2,6-dichlorophenyl-3,3-bis(indolyl)methane loaded on Amberlite XAD-16, Food Chem. Toxicol. 48 (2010) 891.

[320] R.K. Sharma, P. Pant, Preconcentration and determination of trace metal ions from aqueous samples by newly developed gallic acid modified Amberlite XAD-16 chelating resin, J.Hazard. Mater. 163 (2009) 295.

[321] Jamil-ur-Rahman Memon, S.Q. Memon, M.I. Bhanger, M.Y. Khuhawar, Use of modified sorbent for the separation and preconcentration of chromium species from industrial waste water, J.Hazard. Mater. 163 (2009) 511.

[322] M.A. Maheswari, M.S. Subramanian, AXAD-16-3,4-dihydroxy benzoyl methyl phosphonic acid: a selective preconcentrator for U and Th from acidic waste streams and environmental samples, React. Funct. Polym. 62 (2005) 105.

[323] S.Q. Memon, S.M. Hasany, M.I. Bhanger, M.Y. Khuhawar, Enrichment of Pb(II) ions using phthalic acid functionalized XAD-16 resin as a sorbent, J. Colloid Interf. Sci. 291 (2005) 84.

[324] A. Tunceli, A.R. Turker, Flame atomic absorption spectrometric determination of silver after preconcentration on Amberlite XAD-16 resin from thiocyanate solution, Talanta 51 (2000) 889.

[325] A. Tunceli, A.R. Turker, Speciation of Cr(III) and Cr(VI) in water after preconcentration of its 1,5-diphenylcarbazone complex on amberlite XAD-16 resin and determination by FAAS, Talanta 57 (2002) 1199.