uv-photooxidation as pretreatment step in inorganic analysis of environmental samples

ELSEVIER Analytica Chimica Acta 325 (1996) Ill- 133

ANALYTICA CHIMICA ACTA

Review

UV-photooxidation as pretreatment step in inorganic analysis of environmental samples

Jerzy Golimowski a, Katarzyna Golimowska b ’ Warsaw University, Faculty of Chemistry, Pasteura I St.. PL-02-093 Warsaw, Poland b School of Medicine, Faculty of Pharmacy, Banacha 1 St., PL-02-098 Warsaw. Poland

Received 2 June 1995; revised 20 December 1995; accepted 2 January 1996

Abstract

Many laboratories deal with the determination of heavy metals, carbon, nitrogen and phosphorus. The first step in chemical analysis is a proper preparation of the investigated samples. The presence of organic substances can cause problems in many analytical methods. This paper describes the application of UV irradiation as a method of destruction of organic matter in the investigated samples.

Keywords: Environmental analysis; Review

1. Introduction

Many laboratories deal with the determination of heavy metals, carbon, nitrogen and phosphorus in natural samples. A large percentage of these are liquid samples, for instance: water, sewage, body fluid or beverage samples. The first step in chemical analysis is a proper preparation of the sample to be investigated. The determination of metal concentrations is carried out using molecular spectrophotometric, atomic absorption spectrometric and electrochemical methods. All of them require homogeneous samples, free of organic matter which can hinder metal determination by interaction with metal ions. The first step in C, N and P determination is mineralization of the sample.

Organic compounds interact with metal ions in various ways. Organic ligands may form complexes with metals preventing them from reduction at the

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electrodes in the process of electrochemical analysis, or shift the electrochemical reduction and oxidation potential. Some of these complexes are labile, i.e., the metal ions can be readily replaced by hydrogen ions and thus the complex will decompose when acidified, whereas other complexes are resistant to such acid action.

Dissolved organic matter (DOM) can also hinder determination by its interaction with the electrode material. DOM itself can undergo electrochemical reduction or oxidation. As a result, increased background currents are observed occasionally making measurements impossible. The presence of DOM can shift the peak potential and distort the signal. DOM can also adsorb on an electrode surface thus limiting its active surface area. This is particularly undesir- able for the adsorptive voltammetry methods which have become prominent in recent years. Using these methods one can determine metals that do not form

112 J. Golimowski, K. Golimowsku /Analytica Chimicu Acta 325 (1996) I1 l-133

amalgams thus extending the application scope of voltammetric methods.

The presence of organic substances can cause problems in metal extraction during the preconcentration step when atomic absorption spectrometric (AAS) methods are employed. Additionally it can impair nebulizer performance in the case of flame atomisation.

The presence of the DOM in investigated samples makes easy application of electrochemical and AAS methods difficult or even impossible. Hence proper preparation of a sample, in particular elimination of organic matter, is of great importance. Some analytical procedures allow wet digestion consisting of sample evaporation followed by sample heating with concentrated acids, but this may cause additional contamination.

A much better alternative is mineralization with UV irradiation. An investigated sample with a small addition of oxidants undergoes UV irradiation. This method is effective and at the same time it does not contaminate the sample which is friendly to the environment. The total carbon (TC) estimation in- volves conversion of particulate and dissolved organic carbon into CO, followed by CO, determination. Originally, a thermal method of carbon compound oxidation was used for the TC determination. Addition of various oxidants (H3P0,, HNO,, K,S,Os) was reported, determinations being conducted in higher temperatures too. Nowadays the irradiation of a sample with UV, giving the possibility of conducting the process at low temperatures, is applied in many commercial analysers.

The widespread, classical Kjeldahl method for nitrogen determination requires sample heating with concentrated sulfuric acid to the boiling point for up to 4 h. Later modifications to the method involved addition of perchloric acid, hydrogen peroxide, hy- posulfite and various catalysts. The mineralization process results in quantitative nitrogen conversion to ammonium sulfate which gives ammonia during alkaline distillation and is determined afterwards by titration. It was found, however, that during UV irradiation the organic compounds containing nitrogen as well as ammonium ions were oxidised to nitrates and nitrites and these in turn can be determined by molecular spectrophotometry. The application of UV-mineralization eliminates the need for

use of highly corrosive reagents like concentrated acids, and excludes the production of noxious vapours and large amounts of chemical wastes (e.g., NaOH,

Na,SO,, K,SO, etc.). The classical analysis of total phosphorus content

consists of 1 h sample digestion with sulfuric acid and sodium persulfate. Orthophosphates formed are determined spectrophotometrically by the molybdate method. The principle of the new mineralization method is UV irradiation of a sample under addition of persulfate. The use of the UV-mineralization gives similar advantages in the determination of nitrogen.

The UV-mineralization has also been used in the flow systems of automatic analysers for the determination of carbon, nitrogen, phosphorus and toxic metals.

2. Mechanisms of destruction of organic matter by UV radiation

The destruction of organic matter by UV radiation is well known. Water and air are commonly disin- fected using mercury lamps [I]. They have also been applied for sterilisation of various objects, water in cosmetic industry, water in electronic industry, water in swimming-pools etc.

The mechanism and products of UV radiation decomposition have been described for many organic compounds, for instance: DDT (1,1(4,4’-dichlorodi- phenyl)2,2,2-trichloroethane), HCB (hexachloro- benzene), PCP (pentachlorophenol), TNT (1,3,5,-tri- nitrotoluene) [2], atrazine (a herbicide) [3] and others decompose following absorption of 180-250 nm radiation.

The UV-photooxidation in nature was observed and investigated in detail. Similar processes are also used in industrial decomposition of toxic substances, in treatment of urban and industrial waste waters and in production of ultrapure water for trace analysis. This was the topic of many papers in which mechanisms of photooxidation were proposed. These studies give much information which is important for analytical methods, hence in Section 2, also the mechanisms of photooxidation based on natural processes and on those applied in industry are described.

The action of UV light on dissolved organic and inorganic compounds results in the formation of

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many intermediate compounds [4]: excited states of DOM, hydrogen peroxide, singlet oxygen, hydrated electrons, superoxide ions, organoperoxy radicals, hydroxyl radicals and halogen radicals. Mineraliza- tion can also entail the addition of substances which facilitate the oxidation process such as: H,O,, O,, K,S,O,, K,Cr,O, as well as HNO, and others. In such cases, UV irradiation has a catalytic character.

instance, dyes like rose bengal or methylene blue which can act like natural sensitizers. The addition of these compounds and the subsequent exposure to sunlight is recommended as one of the methods of waste water treatment [71.

2.1. Oxidants formed under the influence of UV

radiation

2.1 .I. Singlet oxygen As a result of the action of UV radiation on

molecular oxygen, it changes its energy state from the ground (triplet) state to the excited (singlet) ‘0, state [5], which is probably generated at h = 366 nm [6]. This process occurs in the presence of sensitizers e.g. humic acids present in natural water [7].

Singlet oxygen is highly reactive; its lifetime in water is ca 2 ps [5] and its steady state concentration [‘O,],, is ca lo-l2 mole l- ‘. It was shown that there is a linear relationship between this concentration and the concentration of dissolved organic carbon (DOC), confirming the already shown mechanism of formation of the singlet oxygen [7]. The cited authors also investigated the influence of pH on the reaction rate for the reaction of ‘0, with an acceptor A (the reaction of oxidation of furfuryl alcohol). In the pH range specific for natural waters they did not find any dependence, but for basic solutions (pH > 8) the photooxidation rate decreased.

Kautsky [8] was the first to propose an oxidation mechanism in the natural environment: the energy of sunlight becomes absorbed by the sensitizers, then it is transferred to the 0, molecules and the molecules change their energy state to ‘0,. The formed singlet oxygen atoms react with water and the organic substances present forming peroxides and radicals. Haag and Hoigne’ [7] propose the following scheme de- scribing possible processes that occur during UV-energy absorption:

S+hu+S* +O/02+S (1)

‘0, + 0, (2)

‘O,+A+O,+A (3)

‘0, + A + products (4)

where, S and S * are the sensitizer e.g. humic acid in the ground and excited state, respectively, and A is the energy acceptor compound (trapping agent). Re- action (1) shows how the sensitizer participates in the process, reaction (2) shows physical quenching of excited oxygen molecules by water, reaction (3) shows physical quenching of excited oxygen molecules by an organic acceptor e.g. furfuryl alcohol and reaction (41 shows the chemical reaction with A.

All these data indicate that singlet oxygen is an important intermediate product of organic substance decomposition, which relates to the organic substances from natural sources and those polluting the environment.

2.1.2. &peroxide radicals Oz-m and alkylperoxy radicals ROF

The first product of reduction of an 0, molecule is a superoxide ion 0,. . It is unstable in aqueous solutions and quickly disproportionates to H,O, and 0, [9]. The authors of the paper gave one of the possible mechanisms of the formation of this ion. It is known that humic acids contain quinone and semi-quinone structures, which become excited when they absorb UV radiation. These then react with molecular oxygen to superoxide ions. These ions can participate in the decomposition of some pollutants e.g. in a photochemical dechlorination of methoxy- chlor.

The alkylperoxy radical ROY represents another type of radicals formed in aqueous solutions containing DOM during UV irradiation. Mill et al. [lo] evaluated the ROY concentration at 10e9 M in their investigations of cumene and pyridine photooxidation.

2.1.3. Ozone Apart from the sensitizers occurring in natural Under the influence of the short wavelength UV

waters, one can introduce chemical compounds, for radiation (h < 240 nm), oxygen molecules react to

114 J. Golimowski. K. Golimowska/Analytica Chimica Acta 325 (1996) III-133

form ozone molecules:

In a mercury lamp, the 185 nm line is mainly responsible for the formation of ozone. In darkness and at room temperature, ozone is moderately stable, half-life period being 15 h [l], but when irradiated with 200-300 nm light it decomposes rapidly in a chain reaction [ 11 I:

03+hY-)O+02

o+o,+o; +o,

0; +03-+202+o

where 0; represents excited oxygen molecules. The presence of oxygen or other gases (CO,, N, ,

Ar), however, inhibits the decomposition of ozone, strongly decreasing the reaction rate.

In aqueous solutions, ozone irradiated with UV forms OH. radicals, which are non-specific oxidants. Various pathways of OH0 formation are possible [ 12,131, peroxy (HO;) and superoxy (0;) ions being formed as intermediates in the dissociation of H,O,

03+HzO+hv+H,0,+0,

H,O, + hu --) 20H.

H,O, c, HO; + H+

HO, +O,-+O;‘+HOF

HO: ti H++ 0;.

o,+o;* ‘0;. +o,

0;. + H++ OH’ + 0,

Ozone is an efficient oxidising agent for organic compounds found in nature. In particular, the process of decomposition of humic acids in most types of water was investigated; it was found that their concentration decreases during the process of ozonization [ 141. The decomposition of humic acids follows through gradual decay to compounds with a simpler structure, till,the resulting species have a molecular mass of less than 1000, then being easily biodegrad- able [15]. When examining these processes, Gilbert [16] indicated that 3-4 mg 0, per mg of DOC are enough to decrease the chemical oxygen demand by 60%.

The oxidation processes making use of 0,, H,O, and LJV irradiation, and a comparison of their efficiencies of decomposition of many organic compounds present in natural waters and waste waters were investigated [ 12,17-241. The oxidation rate increased always in oxidant/UV systems compared to systems with oxidant only.

2.1.4. OH ’ radicals and hydrogen peroxide It was shown that photooxidation processes in

natural water under the influence of sunlight have also a radical character. The formation of OH0 radicals and their subsequent reaction with organic matter is one of the natural ways of biodegradation [4,10,25-271.

The mineralization processes used in laboratories also make use of the high reactivity of hydroxyl radicals, which were generated from hydrogen peroxide added to the solution. When exposed to the action of UV light, H,O, decomposes forming OH0 radicals, which initiate the radical chain reactions involving organic substances contained in mineralized samples.

It was found that oxidation by hydroxyl radicals is most efficient in the pH range 6-8. Malaiyndai et al. [28] checked the efficiency of mineralization of a water sample using an H,O,/UV system. When using 0.5% (v/v) H,O, they achieved an 88% reduction of TOC content in distilled water and at least 98% in tap water. They found that increasing the H,O, concentration up to 1% (v/v) did not improve mineralization efficiency. The optimal dura- tion of the mineralization was set to 4 h. Authors also compared the mineralization efficiencies of an H,O,/UV system (88% reduction of TOC content) and a UV-only system (28% reduction). They indicated that an 8-h ozonization is much less efficient in the removal of non-polar organic compounds from water than the H,O,/UV system.

The influence of the addition of H,O, on the efficiency of UV-digestion of many organic compounds in aqueous solutions was studied [ 17,29-311.

An often used decomposition method consists of acidifying (pH 2) mineralized samples containing H,O, and subsequent photooxidation. This method was initially used for DOC determinations in which the formed CO, was measured using IR spectroscopy. It was found that the decomposition of

J. Golimowski. K. Golimowska/Analytica Chimica Acta 325 (1996) 111-133 115

organic substances is quantitative. An additional effect of acidifying is the dissociation of labile metal complexes of organic compounds. The H,O, photooxidation conditions are given in the paper by Dorten et al. [32].

Nitrates and nitrites occurring in natural water can also be the source of OH’ radicals:

NO; +H,O+hv+NO+OH-+OH.

NO, + H,O + hu + NO, + OH-+ OH.

Kotzias et al. [26] investigated the rate of decomposition of several model organic compounds dissolved in water and irradiated with UV. They compared rate constants of the photooxidation reaction in pure water and in water containing nitrates and nitrites. In the presence of these ions, the decomposition was always faster; for example, the rate constant for the decomposition reaction of 4nitrophenol was 13 times higher in the presence of nitrites and 5 times higher in the presence of nitrates. So the presence of nitrate ions reduces the time needed for a decomposition of organic compounds contained in the examined solution, which recommends the use of nitric acid in the mineralization of natural samples. However, one should remember, that during the W irradiation of nitrate ions, nitrite ions can be formed, which hinders voltammetric determinations.

2.1 S. Per-sulfate ion One of the strongest oxidising agents in aqueous

medium is the persulfate ion. The standard red-ox potential for the reaction:

2SO42- (aq) * S,O,2- (aq) + 2e

equals -2.01 V [33]. The first stage of decomposition of this ion is of radical character:

s,o,2- + 2so;.

This reaction can be initiated by substances contained in a solution as well as by the sunlight. In the second stage of reaction the sulfate radicals react with water to form hydroxyl radicals:

SO;’ + H,O + HSO; + OH.

The next stages of chain reaction of the S,Oi- decomposition are:

S,O;- + OH’ + HSO; + SO;. + l/20,

SO;. + OH. + HSO, + l/20,

The strong oxidising properties of S,Oi- ions, due to the formation of H,O,, 0, and OH0 as reaction products, means that persulfate is commonly used in mineralization by UV radiation. Van Steen- deren and Lin [34] studied the degree of mineralization of potassium phthalate (a recognised organic carbon standard), EDTA and DL-valine at concentrations of up to 20 mg 1-l C. They added K, S,O, to the samples and pumped them through a quartz coil around a 150 W mercury lamp. They varied the type of catalysts, their concentrations, intensity of UV radiation, length of the coil, temperature and pH of the examined solution. Finally, they found that there are only two decisive factors that influence the efficiency of DOC mineralization: K,S,O, concentration and UV radiation used.

2.1.6. Titanium dioxide It has been shown that many organic compounds

could be photooxidized to CO, using TiO, as a catalyst. The mechanism of this process is believed to involve positively charged holes and electrons formed on the surface of excited TiO,. Energy greater than semiconductor band gap excites an electron from the valence band (vb) into conduction band (cb), creating an electron (e&hole (h) pair [35]:

TiO, + hv + e,b + h:,,

At the surface of TiO, these may react with adsorbed species, e.g. oxygen [36-381 and create in water solutions the active radicals (0;’ , OH’ and others) which subsequently decompose organic substances.

The influence of temperature, amount of TiO,, concentrations of oxygen and decomposed substances on the rate of CO, formation was investigated [36,39,40].

Titanium dioxide can be used either as a powder suspended in water solution [35,36,38,39] or attached to a stationary glass 140,411 or to polytetrafluoroethy- lene (PTFE) tubing [42] coiled around a UV-lamp (often a ‘black-light lamp’). This catalyst is used in flow-injection analysis of TOC in water solutions at low concentration of organics (0.1-30 pg/ml). It was also shown that if nitrogen, phosphorus, halo- gens and sulfur were present in organic compounds, they were converted to NH: and NO;, PO:-, X- (halide) and SO:-, and could subsequently be determined [37,41].

116 J. Golimowski, K. Golimowsko / Analytica Chimica Acta 325 (1996) I I I-133

2.1.7. Other oxidising agents

The application of KMnO, and K,Cr,O, in photooxidation was studied by Korolev et al. [43]; also Frimmel and Winkler [44] discussed the possible use of these oxidants for acceleration of the photodecom- position of organomercury compounds. It was found that the best addition in the process of UV-mineralization of these compounds (with Hg concentration in the pug 1-l and ng l- ’ range) is a 0.01-0.05 M K,Cr20, solution. Complete decomposition oc- curred after 2 min. Spectra of organomercury compounds indicate their strong absorption in the range 200-260 nm.

The addition of metallic mercury or mercury(B) compounds as sensitizers in the UV-mineralization process is a well known fact [43]. Semenov et al. [45] used them in the mineralization of samples of natural water in which C, P and N were determined. The complete decomposition was achieved already after 5-10 min of irradiation.

Some of the well known catalysts were also applied for UV-photooxidation, e.g. Ce(SO,), [43,46,47], UOz(N03)2, 0~0, 1471, Pt [43]. These are, however, rarely used.

The reactions of formation of intermediate oxidising compounds and their influence on organic matter contained in solutions was described above. In the UV-mineralization in laboratory conditions many of the mentioned processes take place simultaneously, for instance, ozone formed from oxygen generates OH0 radicals in the reaction with water molecules. It is believed, however, that the OH’ radicals are most important in the oxidation of organic matter. They can be generated directly from hydrogen peroxide under the influence of short UV and for this reason H,O, and S,Oi- are the most frequently added oxidants in the UV-mineralization.

3. UV radiation sources

The UV radiation wavelengths extends from 40 to 400 nm. This range has been,divided by the Com- mission Intemationale de 1’Eclairage into 3 sub- ranges: UV A (400-315 nm), UV B (315-280 nm), UV C (< 280 nm>. The natural source of UV radiation is the sun, the most frequently used artificial sources are mercury lamps.

L 1

1. loo 160 200 260 300 350 400

wavelength [mu]

Fig. 1. Spectrum of mercury in UV range.

,

d 600

In 1835, Wheatstone found out that intense light accompanies the evaporation of mercury in an electric arc. Jackson and Soho patented the first mercury lamp, but it was only in 1896 when Dowsing and Keating built a type of lamp which is presently used.

The mercury spectrum is rich in lines in the UV range [48] (Fig. 1). The transition energy of Hg atoms from the lowest excited state (63P,) to the ground state (6’S,) corresponds to the wavelength of h = 253.7 nm. This is a resonance line. Thanks to the relatively low mercury ionisation potential (10.34 eV> the avalanche effect of generating ion-electron pairs can be quickly achieved. The convenient value of mercury vapour pressure at room temperature allows attaining the necessary pressure for the resonance line generation. Mercury, as a relatively inert element, neither reacts with the electrode material nor with the bulb material.

Apart from mercury vapours, mercury lamps contain a noble ‘gas, usually Ar. Though it does not participate directly in the photon generation it in- creases the number of current carriers: electrons and ions. In an elastic collision between an electron and an atom the part of the energy of the electron is transmitted to the atom causing its excitation and starting processes taking place in a lamp. These can be described with following equations [49]:

- during the lamp ignition:

e+Ar+Ar* +e Ar* +Hg+Hg++Ar+e

- during the lamp operation:

e+Hg-+Hg’+e

Hg* +e+Hg’+2e

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When the electrons do not transfer sufficient energy for the single-step reaction, the ionisation process proceeds stepwise.

- in the lamps with higher Hg vapour pressure:

Hg* +Hg* -)Hgl +e

Hg* +Hg* +Hg++Hg+e

The current flow through gases in the arc discharge zone is described by a negative voltage-current value (which is reversed when compared with solid conductors) [ 11. The negative voltage-current dependence causes instability of the discharge process (current flow). Small voltage oscillations can lead to a fatal increase of the current causing destruction of the lamp. To compensate for the negative dependence a resistance (so called ballast resistance) is inserted in the lamp circuit. The combination of the resistance and the lamp results in a positive value. If a lamp runs in a direct current circuit, the ballast resistance can be replaced with an impedance element. The value of an alternating current lamp is more complicated, because the discharges can stop in every part of a cycle and the value can be partially positive in a cycle. Discharges at high frequencies have an almost ohmic character, because the almost constant electron density cannot follow the field

changes. A characteristic parameter of mercury lamps is

the value of the mercury vapour pressure. Mercury lamps are divided most often into 2 groups: low- pressure lamps (Hg pressure 0.1-l Pa (1O-3-1O-2 Torr) and high-pressure lamps (Hg pressure > 0.1 MPa (1 atm). One can find, however, a more detailed division specifying medium-pressure lamps (ca. 0.1 MPa) and high-pressure lamps (ca. 10 MPa).

3.1. Low-pressure lamps

This type of mercury lamps is shaped as a long tube made of glass. The lamps are 1 m long and 15-40 mm in diameter. Each end of the lamp contains a built-in tungsten electrode. The gas closed in the lamp bulb contains a mixture of Hg vapours (O.l- 1 Pa) and a noble gas, predominantly Ar, under pressure of hundred Pa. A drop of mercury is introduced into a lamp and the main part remains liquid during lamp operation. The Hg vapours formed re- main in equilibrium with the liquid Hg. The pres-

sure-temperature relationship is described by the saturated vapour pressure curve. The 0.1 - 1 Pa pressure of Hg inside the lamp is only possible when the temperature of lamp walls is kept at 40-60°C.

The spectrum of a low-pressure lamp consists of almost only 2 lines: the resonance line at 253.7 nm of the 63P, + 6l S, transition and the line at 184.9 nm corresponding to the 6lP, + 6’S, transition. A small number of Hg atoms is excited to atomic states higher than 6’P, but their lines are weak. The ratio of the 184.9 nm line intensity to the 253.7 nm line intensity equals 0.12-0.34 depending on the bulb temperature and the arc current. The maximum value of the ratio is attained when both parameters reach their upper limiting values. In many cases, the 184.9 nm line is unwanted, due to the known harmfulness of this radiation. To eliminate it a special external filter or carefully chosen bulb material is used.

Low-pressure lamps have a long operating time of 5000-10000 h, though, frequent switching on a lamp makes it shorter. Their maximal power is 60 W. The detailed dependence of lamp efficiency of transform- ing supplied electric energy into resonance radiation by a low-pressure lamp was given by Phillips [49]. This efficiency depends on: temperature, noble gas pressure, lamp geometry, supplying current intensity and its frequency. The low-pressure lamp efficiency, in the UV C radiation range, amounts to 40% [2].

The special type of low-pressure lamps, so-called ‘black-light fluorescent lamps’ should also be mentioned. The inside wall of the lamp is coated with the fluorescence substance, e.g. phosphorus, which ab- sorbs the radiation of 254 nm and emits the radiation of around 365 nm. This is called ‘black light’. Glass material used for the walls does not transmit the shorter radiation but allows the longer to pass through. This type of lamps is often applied for photocatalytic oxidation of organic substances in solution with titanium dioxide as a catalyst. The flow- injection determination of TOC can hence be conducted in a borosilicate apparatus, which is cheaper than quartz one, needed in the case of shorter UV radiation [40-421.

3.2. Medium-pressure and high-pressure lamps

These lamps are shorter and much narrower than the low-pressure lamps with equal power. They are

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lo-150 cm long and lo-40 mm in diameter. Shorter lamps are also produced and they are used for special applications. Almost all medium-pressure lamps are alternating current lamps. Both electrodes have the same construction and they work alternatively as a cathode and as an anode. During lamp operation, all mercury evaporates so that the Hg pressure depends on the amount of it and the pressure-temperature relationship is described by gas laws. Medium- pressure lamps operate in the state of the so-called local thermal equilibrium, which means that the temperature of atoms and ions equals the temperature of electrons which is 5000-8000 K. In a low-pressure lamp the temperature of electrons (ca. lo4 K) is much higher than the temperature of atoms and ions (ca. 500 K). The pressure corresponding to the maximal plasma temperature equals several tens of kPa, depending on the lamp diameter. The temperature of the walls should be kept between 600°C and 900°C to achieve optimal operating conditions. Below 600°C the mercury vapours may condensate and over 900°C the wall material can change its properties. Therefore it is important to have proper cooling. Medium-pressure lamps are air-cooled, and high-pressure lamps are water-cooled.

The plasma at the lamp operation temperature contains a certain number of excited atoms. The transitions from these levels contribute to the irradiated energy. The spectrum of a medium-pressure lamp is richer than the spectrum of a low-pressure one. Apart from the single emission lines, it also contains an emission continuum, especially in the UV C range. Related to the energy consumed by the lamp torch the contributions to each UV range are as follows 121:

UV C (180-280 nm) 16%; UV B (280-315 nm) 7%; UV A (315-400 nm) 7%. The sum of these fractions gives only 30% of the

torch power. 15% of the power is converted into visible radiation and 35% into thermal radiation (IR and lamp walls radiation). The remaining 20% is lost in the process of heat conduction on the electrodes. The lamp operation time is ca. 2000 h.

3.3. Additional remarks

The material of the lamp bulb must comply with many conditions. The most important among them

are: UV radiation transmittance, chemical resistance to the substances contained in a lamp, strength at elevated temperature and pressure. Quartz glass represents this kind of material. Its properties are determined by the type of mineral used and the melting method. Melting can be carried out in an electric oven (I) or in an oxygen-hydrogen flame (II). The quartz glass prepared using the latter (II) method, has better transmittance in the shorter wavelength range.

Below some reserved names are given for the produced quartz glass with relation to production method:

method I: Vitreosil, Infrasil; method II: Homosil, Herasil, Ultrasil. The detailed transmission spectra for these materi-

als as well as for other materials obtained by a synthesis from volatile silicon compounds (e.g. SiCl,) are presented in [49].

The intensity of irradiation depends, of course, not only on the type of lamp used, but also on the distance between the source of radiation and the sample. For the short distances from a linear source an irradiation intensity is indirectly proportional to the first power, and for the longer distances (multiple of lamp lengths) to the second power of the distance

1471. The data found in the chemical and analytical

literature concerning the types of used mercury lamps can be inexact. In some papers, surprisingly high electric power (e.g. 400-600 W) is assigned to the lamps described as low-pressure. If this were the case, these lamps would be huge. These were probably medium-pressure and not low-pressure lamps. This chapter tries to set the problems connected with mercury lamps in order.

It should also be mentioned that excimer lasers have been recently applied in UV-mineralization [50]. Decomposition of sodium fulvate and 2,4-dichloro- phenol by monochromatic radiation was investigated. There were used: A = 193 nm (ArF laser), A = 248 nm (KrF laser), h = 308 nm (XeCl laser). Mineral- ization was conducted in a closed 40-ml quartz vessel. The rate of the decomposition increased for shorter wavelengths. Power consumption of a laser and that of a mercury lamp during the decomposition of the same sample were compared. In the case of lasers 100-2000 times less energy was needed. This can be explained by the fact that only a small

J. Golimowski, K. Golimowska / Analytica Chimica Acta 325 (1996) I1 l-133 119

fraction of power taken by a mercury lamp is emitted as UV radiation. This shows new ways of laser application in sample preparation as well as in water purification.

4. Classification of digestion devices

There are in principle three UV mineralization methods. The first one consists of immersing of a mercury lamp into a reaction flask. This technique is similar to the photochemical synthesis in organic chemistry. Frimmel and Winkler [44] used a high- pressure UV lamp to transform organomercuric compounds into inorganic mercury combinations. For the subsequent mercury content determination AAS was used. The reaction flask was kept cool in ice to avoid a temperature rise above 30°C in connection with the mercury compound volatility. During the determination of nitrogen in lake water samples, Manny et al. [5 l] placed a 450 W mercury lamp in a reaction flask which was covered with a quartz cooling jacket containing water. During irradiation for 1.5-3 h, oxygen was purged through the sample. Malaiyandi et al. [28] put a similarly cooled lamp into a sample too. This type of mineralization is not applied in commercial digesters.

The second UV mineralization method is based on the application of batch devices. Armstrong et al. [52] were first to describe this kind of device. It consisted of a mercury lamp situated in the centre and surrounded by symmetrically distributed 100 cm3 test-tubes closed with ground-in Pyrex-glass stoppers. The whole device was installed in a cylin- der made of aluminium foil and its lower part contained a fan for cooling the samples. The mineralizers described by Henriksen [53] and Sipos et al. [54] were similar. They used, however, a different number and volume of test-tubes and a different way of stopping them. Shkil et al. [55] used a digestor with a sample in a jacket surrounding the lamp; the sample was purged with air. On the whole, however, samples are placed in closed quartz test-tubes, thus giving the possibility of simultaneous mineralization of more than one sample. Commercial batch mineralizers can be divided into two types: air-cooled mineralizers and water-cooled mineralizers.

The air flow in the air-cooled digestors is forced

Fig. 2. UV-digester UV-1000, Kiimer Analysentechnik, 83004

Rosenheim, Germany. 1. UV lamp, 2. water cooled lamp holder,

3. sample vessel, 4. cooling water, 5. sample vessel water cooler.

by a fan situated below the lamp and below the test-tubes. This type of digesters are produced by the firm LAR (Berlin, Germany) [56] and the firm MIN- ERAL (Warsaw, Poland).

The second type of stationary mineralizers contains a chamber with a lamp and samples surrounded by a water jacket. The use of the water-cooling system allows the application of high-pressure lamps. Such lamps emit radiation of higher intensity and they produce more heat causing the evaporation of the sample. The regulated water flow makes it possible to adjust the sample temperature.

The digestor UV-1000 from the firm Khmer Analysentechnik (D-83004 Rosenheim, Germany), Fig. 2., belongs to such devices. The water-cooling as well as the oblique orientation of test-tubes causes convectional mixing of samples [3 1,57-591. The 705 UV-digestor produced by the firm METROHM (Herisau, Switzerland), Fig. 3., has besides the water cooling system also a fan installed in the lower part of devices cooling the lamp mounting. According to Kolb et al. [60] one can speed up the mineralization process by means of a controlled temperature rise from 65 to about 94°C. They recommend the high- temperature mineralization (at around 9OT) for aro-

120 J. Golimowski, K. Golimowsku /Analytica Chimica Acta 325 (1996) I II-133

W are applied. These lamps do not need any additional cooling.

The flow digestors in automated carbon, nitrogen and phosphorus analyzers work often in an on-line mode. The samples of surface waters [63], waste waters [64] and also soil extracts [64-661 were investigated. Analyzers of this kind are produced, e.g. by the firm SKALAR Analytical, Breda, Holland [67,68], Fig. 4.

In many flow through systems the PTIX photore- actor is used instead of a quartz one [42,69-731. FTFE is easier in use, less fragile and cheaper; it

Fig. 3. UV-digester 705, Metrohm A.G., 9101 Herisau, Switzer-

land. 1. UV lamp, 2. sample vessel, 3. stopper for sample vessel,

4. sample vessel holder, 5. fan, 6/7 cooling water inlet/outlet.

matic compounds that become decomposed within 60 min. After such mineralization adsorptive voltammetry can be applied for the determination of heavy metals.

In the third UV mineralization method the flow systems are employed. The sample flows through the tube coiled around a fixed UV lamp. Such flow systems were originally used for the TC determination. Goulden and Brooksbank [61] used a flow digestor as a part of an automatic DOC analyser. Their device consisted of a tube with a diameter of 17.5 cm. A 1200 W mercury lamp with a quartz spiral coiled around it, was installed inside the tube and the whole thing was cooled by the air purged upwards. The purge of air was controlled to keep the temperature of the sample leaving the device at about 80°C. In the device proposed by Dorten [32] a sample flows in a jacket around the lamp.

Nowadays the flow digestors are used for nitrogen, phosphorus and other element determination as well. In waste water analysis, using the flow-injection technique, Hinkamp and Schwedt [62] applied a digestor consisting of a 50 W mercury lamp and a PTFE tube coiled around it; the device was cooled from below by a fan. In the early constructions of these type of digesters the high wattage lamps were used, but now mostly the lamps of power of about 10

sampler

r

sparging UV destruction

w% -

4 -

air Hz Hz waste hi2 HCI

b

I I I

quartz coil UV lamp Fig. 4. TOC/DOC analyser SK- 12, Skalar Analytical, Breda, The

Netherlands. (a) Schematic diagram of continuous flow system.

(b) UV-digester unit.

J. Golimowski, K. Golimowska/Anolytica Chimica Acta 325 11996) Ill-133 121

transmits W light above 240 nm, though the transmittance falls below 280 nm (at 260 nm it is one tenth of that of quartz [70]). Its efficiency at low wavelengths is believed to enhance by diffuse radiation transfer and internal reflection [69]. The hy- drophobic surface of PTFE may cause less adsorptive losses of trace metals contained in water samples than the quartz walls of test-tubes or coils, so the use of PTFE is especially recommended in trace metal determination. The disadvantage of this material is the releasing of fluoride ions [70]. The fluoride ions can complex the metal ions, e.g. aluminium, contained in natural water. In the case of the use of

conductivity detectors, the presence of fluoride could result in high background conductance, which would limit the sensitivity of the detector. Using PTFE instead of quartz has to be considered if, in a particular case, the releasing of fluoride and hydrogen ions does not disturb the determination process.

A flow system is becoming more and more popular in analysis, because of its automation, rapidity, small volume of a sample and elegance. The number of elements being determined by this method has been increasing during the last few years. Flow systems are promising on the ground of their sim- plicity (an uncomplicated apparatus, no need for cooling device of a low wattage lamp). The using of F’TFE tubing decreases the cost of the apparatus. On the other hand, this method does not catch up to stationary voltammetric methods regarding the sensitivity in the range of extremely low concentrations. As a result of digestion in a batch system a large

Table 1 Examples of commercial UV-digesters

volume of samples is received, which enables the determination of many elements in routine analysis by flame atomic absorption spectrometry (FAAS). So far the mineralization in batch systems is better documented in the literature - the number of studied compounds, which undergo the destruction by UV irradiation in batch systems, is significantly greater than that in flow systems. It is difficult to decide which system is better, both exist in parallel and are used for different tasks.

The separate part in all digestors is the supply system powering the lamp. In the most simple case the system consists of a choke and a lamp connected in series. The circuit can be completed with a balanc-

ing capacitor. There is another type of power supply that incorporates a dissipative transformer. Some other types of lamps require an additional starting system. High-pressure lamps (lamps with electric power above 150 W and of elongated shape) require 380 V power supply or an electronic powering system with a built-in starting system unit.

The main types of digestion devices and their technical parameters are presented in Table 1.

5. Application of UV-photooxidation in analysis

Each method of determination of elements in solution requires homogenous samples. UV-digestion as a preliminary step in an analysis of heavy metals, carbon, nitrogen and phosphorus can meet this re- quirement.

Manufacturer uv-lamp (W) Configuration Temp. CC) System

LAR, Berlin, Germany UV-88

Mineral, Warsaw, Poland UV digester R-6

Kiirner Analysen-Technik, Rosenheim, Germany UV-di-

gester UV- 1000

Metrohm, Herisau, Switzerland UV-digester 705 Skalar Analytical B.V. Breda,

The Netherlands UV-digester SA 5550

750

125 or 250

loo0

500

8

20 test-tubes u = 25 ml batch air-cooled

around the lamp

8 test-tubes u = 50 ml < 80 batch air-cooled

around the lamp 12 test-tubes u = 25 ml batch water-cooled

around the lamp oblique

orient.

12 test-tubes v = 12 ml 60-94 batch water-cooled around the lamp air-cooled

spiral coiled around the 70 (N) 97 (P) continuous flow

IamP

122 J. Golimowski, K. Golimowsku/Adytica Chimica Acta 325 (1996) Ill-133

The first use of UV-photooxidation as a digestion process of water samples for subsequent determination of carbon, nitrogen and phosphorus was done in 1966 by Armstrong et al. [52]. The application of this method as a pretreatment step for determination of metals (mercury) was done in 1975 by Frimmel and Winkler [44]. These reports originated the study on UV-digestion, especially by electroanalysts, who determined the metal concentrations in waters by

voltammetry. The development of flow systems cap- tured again the chemists’ interest on photooxidation as a step in carbon, nitrogen and phosphorus determination. Nowadays, these elements are willingly determined by the use of commercially available automated analyzers, containing the UV-unit. The terms: ‘total (UV) nitrogen’ and ‘total (UV) phosphate’ have been introduced to distinguish this method of pretreatment from the classical methods. The application of flow systems for metals determination has not been yet so commonly used, probably because of difficulties with automation of detection methods; AAS and spectrophotometry can be easier adopted for this purpose than voltammetry.

The UV-photooxidation seems to be irreplacable for water and waste water analysis, because of low concentration of investigated elements, so the application of other digestion methods could cause the contamination.

5.1. Metal determination

Many metals have been determined in various types of matrices. The voltammetry and AAS method have been mainly used as the determination techniques. The condition for the UV digestion process depends on the element which should be determined, on the method of determination and on the matrix.

For the determination of almost all metals the mineralization process is usually conducted in acidic medium to avoid a precipitation of salts. Only the digestion of the sample containing chromium, which should be subsequently determined by voltammetry, is performed in neutral medium [74,75]. For both methods of determination, a sample has to be homogeneous; for voltammetry it should be also com- pletely mineralized, whereas the AAS techniques admit samples only partly mineralized.

Numerous studies deal with the determination of metals in natural waters: copper, lead, cadmium and

zinc [57,60,75,76], lead and cadmium [77], copper [54] and also mercury [44,54], chromium [74,75], iron [78], arsenic [79,80], antimony and bismuth [Sl] were determined in natural water and snow. The presence of high contents of humic acid in water requires a special treatment of samples; optimal conditions of mineralization were assessed by Labuda et al. [57]. They used very short time of UV irradiation with a 1000 W lamp. These procedures eliminated the negative effect of the presence of humic acids on

voltammetric determination (the differential pulse anodic stripping voltammetry (DPASV) method) of Cu, Cd, Pb and Zn. JoAca [82] preparing through-flow water samples for subsequent metal determination, found a precipitate (probably humic acid) in his acidified samples stored in a refrigerator. Such precipitation can involve a co-precipitation of trace elements. The same samples after acidifying and irradiation with UV could be stored without forming any precipitate.

Waste water is also a very often studied matrix in which the concentration of Cu, Pb, Cd and Zn [60,76,83], Fe [78], Hg [84] and arsenic [79] are determined. Investigating this type of samples, JoAca 1821 found a non-uniform distribution of metal concentrations in the samples, which was probably caused by the bacteria present in the solution. In the process of bacteria growth, metals participate in their metabolism and become concentrated in the bacteria colonies formed. The observed non-homogeneity was eliminated after the UV-mineralization. The samples decomposed using the UV-method can be stored and subsequently analysed by AAS (the nebulizers do not become blocked during the measurement). A special type of waste water is that containing surfac- tams. The conditions of digestion of such samples were investigated [76,85].

The bioavailability of four heavy metals (Cu, Pb, Cd, Zn) can be indirectly investigated by determination of their concentration in soil extracts [86-881 or in interstitial water of sea sediments [89]. It could be difficult to find other digestion methods suitable for such samples because of their salinity. The same metals and nickel and cobalt were determined in extracts obtained during leaching of domestic waste and compost produced from it [90,91]. Chromium(II1) was determined by AAS in leather extract, which is also a very complicated matrix. [58]

J. Golimowski. K. Golimowska/Analytica Chimica Acra 325 (1996) 111-133

Table 2

Application of UV-photooxidation in determination of metals

Sample Condition of photooxidation Metals/method of determination Reference

Natural water, wine UV-lamp 150 W, I = 12 h, pH 2, Cu. Hg/DPASV-RDE-Au [541 add. H,b,

Wine

Wine

Waste water

River water

Natural water

River water

River water and industrial waste

water containing surfactants

River water, snow

Water, waste water, snow

Model solutions, natural water,

municipal waste water, effluent

from galvanic bath Model solutions, municipal waste

water

Surface water

Water

Water, waste water

Model solutions, beverages, biological samples Interstitial water of sediments

Model solutions,

river water

Compost extracts

Compost extracts

Soil extracts

Leather extracts

Sample of fish meat after ‘wet digestion’

UV-lamp 500 W, t = 1.5 h, add.

H,O, UV-lamp 150 W, [=0.5-l h,

add. H,O,

UV-lamp 150 W, r = 4-6 h, pH

2, add. H,O,

UV-lamp 800 W. r = 2 h, pH 2,

add. H,O,

UV-lamp 150 W, I = 2-3 h, pH

2, add. H,O,

UV-lamp 150 W, t = 2-3 h, pH

7-8, add. H,O,

UV-lamp 250 W r 4 40 mm,

add. H,SO, + H,O,, HCOOH, HCOOH + H,O,

UV-lamp 150 W, pH 1

UVlamp150W,r=2h,pH2,

add. H,O, UV-lamp 500 W, r = 1 h, pH 2, add. H,O,, temp. 90°C

UV-lamp 500 W, r = 1 h, pH 2, add. H,O,, temp. 90°C Immersion UV-lamp, r = 30 min.

pH < 1, add. K,Cr,O,, temp. 30°C

batch system: UV-lamp 1200 W,

r = 15 min, add. K,S,O, or

H,O,, pH variable flow system:

add. K,S,O,, pH basic

UV-lamp 450 W, r < 4 h, add.

H,O,, pH basic UV-lamp 500 W, r=0.5-6 h,

pH 2, temp. 90°C UV-lamp 150 W, r = 3 h, pH 2, add. H,O,

UV-lamp loo0 W, r = 10 min,

pH 2 or I = 2 min, add. H,O,

r=lO min or r=5 min. add.

Hz02 UV-lamp 125 W, r= 3-10 h,

pH 2, add. H,O, or K,S,O, UV-lamp 125 W, r= 5-10 h,

pH < 2, add. H sOa UV-lamp 150 W, r= 50 min. add. 0,

UV-lamp loo0 W, r= 15 min.

add. H,O,, HN03 UV-lamp 700 W, r = 30 mitt, add. H,O,

Pb, Cd/DPASV-MFE,

Cu/DPASV-HMDE Cu, Cd, Zn/DPASV-MFE

Cu, Pb, Cd, Zn/DPASV-HMDE

Pb, Cd/DPASV-MFE, Zn,

Cu/DPASV-HMDE

Cu. Pb, Cd, Zn/DPASV-

HMDE, DPASV-MFE

Cr/AdDPCSV-HMDE

Cu. Pb, Cd, Zn/ASV

Sb, Bi/DPASV-HMDE Fe/DPV-HMDE

Cu, Pb, Cd, Zn/DPASV- HMDE, Ni, Co/AdDPCSV- HMDE

Hg/DPASV-RDE-Au

Hg/AAS-cold vapor, GC-MS benzene extract

As/AAS

As/AA& spectrophotometric A

= 520 nm Pb. Cd/DPASV-HMDE, Pt. Ni,

Co/AdDPCSV-HMDE

Cu. Pb, Cd, Zn/DPASV-

HMDE. Ni/AdDPCSV-HMDE

Cu. Pb, Cd, Zn/DPASV-HMDE

Cu, Pb, Cd, Zn/DPASV-

HMDE, Ni, Co/AdCSV

Hg/DPASV-SDE-Au

Cd, Pb, Cu. Zn/DPASV-

HMDE, Cd, Pb < 0.2 ng

g- ‘/DPASV-MFE

Cr/AAS

Hg/DPASV-RDE-Au

[921

[931

[831

[771

t751

L74.751

[761

(811 b’81

Ifa

1841

[441

(801

[791

t941

[891

(571

@ol

[911

[86-881

[581

[951

123

124

Table 2 (continued)

J. Golimowski, K. Golimowska/Anolyrica Chimica Acra 325 (1996) III-133

Sample Condition of photooxidation Metals/method of determination Reference

Sample of bird feather after mi- UV-lamp 125 W, f = 2 h, add. Hg/DPASV-SDE-Au [%I cro wave digestion HID,

t - time of UV irradiation, add. - addition of....

Method of determination: AAS - atomic absorption spectroscopy, GC-MS - gas chromatography-mass spectrometry, DPV -

differential pulse voltammetry, ASV - anodic stripping voltammetry, DPASV - differential pulse ASV, AdCSV - adsorptive cathodic

stripping voltammetry, AdDPCSV - adsorptive differential pulse CSV.

Type of electrode: Ml% - mercury film electrode, HMDE - hanging mercury drop electrode, RDE-Au - rotating gold disc electrode,

SDE-AU - stationary gold disc electrode.

Beverages (juices, wines and others) and body fluids (blood, urine) were also UV-photooxidized for determination of Cd and Pb [92-941, Hg [54], Ni, Co and Pt [94]. The mineralization of wines required relatively high concentration of added oxidants (in the case of H,O, 1:l v/v). The conditions of UV- digestion were chosen so that the ethyl alcohol was oxidized to acetic acid which acted as a supporting electrolyte for voltammetric determination. However, this method cannot be used for sweet wines, because sugar yields carbonization and this heterogenous mixture does not react with H,O,. Body fluids, especially blood, are also difficult matrices. In the process of UV-digestion, Na,EDTA should be added to prevent coagulation; the presence of red blood cells, containing iron, causes the catalytic decomposition of H,O,, so a long time of irradiation is required. The foam formation, caused by proteins, limits the volume of a sample; only diluted samples can be digested by this method. The measurements of platinum concentrations are especially interesting because of its continuous increase in the environment caused by catalysts of cars and by its medical application as a component of cytostatic drugs [94].

The UV-mineralization is also used as a comple- mentary method after closed wet digestion of solid samples and microwave digestion [95,96]. The pressure digestion of samples of fish meat in the first step was followed by the UV irradiation of the diluted sample [95]. Bird feathers (environmental monitoring) were pressure digested in a microwave completed by the following UV-mineralization [96].

The application of UV-radiation in metal determination in water and waste samples has been comprised in the international [97], get-man [98] and polish [99- 1021 standards.

The information concerning the conditions of UV-mineralization and the methods of determination of metals are presented in Table 2.

5.2. Speciation of elements

The other field of application of UV irradiation is speciation of elements. Chemical speciation may be defined as the existence of various chemical forms of an element, which together give its total concentration. Knowing only the total concentration of a metal, one cannot say much about its bioavailability and its circulation in the environment. It is well known, that heavy metals are the most toxic to aquatic life occurring in the form of free (hydrated) ions (however in the case of mercury, its alkyl compounds are the most toxic forms), whereas strongly organically complexed metals or metals as- sociated with colloidal particles are much less dan- gerous for the environment. The biological aspects of the speciation research is the reason why numerous studies deal with natural waters, especially seawater.

The voltammetric determination of a metal in filtered and acidified water samples gives the concentration of free ions and inorganic complexes, whereas the determination of a metal in the sample previously UV irradiated, gives its total concentration (the organic substances are oxidised and the bound metal is released).

In 1976, Batley and Florence [ 1031 proposed a detailed analytical scheme for metal speciation in water. The authors distinguished seven possible forms in which trace metals can occur in water: free metal ions, labile and non-labile bound metals in organic and inorganic complexes, as well as metals adsorbed on organic and inorganic matter. One of the steps of

J. Golimowski. K. Golimowska/Annlytica Chimica Acta 325 (1996) III-133 12.5

this scheme (beside ion exchange on Chelex-100 resin) is UV irradiation of the samples. According to the scheme the chemical forms of dissolved copper, lead and cadmium in seawater [104] as well as the same metals and zinc in natural fresh water and in a tap water [lo51 were determined.

Speciation of the following elements in natural waters with the use of W-digestion of samples were studied: copper [104-l 111, cadmium [104,105,111], lead [104,105], zinc [105-1081, nickel [llO],

Table 3 Application of photooxidation in speciation of elements

chromium [ 1121, mercury [ 1131, iron [ 1081, aluminium [114], tin [115] and iodine [116].

According to Pempkowiak [ 1171, among all methods of speciation analysis described in the literature, particularly those are interesting, which demand neither preconcentration nor separation of individual forms. Such a method is the anodic stripping voltammetry (ASV) technique applied to the acidified and previously UV irradiated sample. The application of a flow system with an in-line digestion unit, pre-

Sample Element Conditions of photooxidation Method of determination Reference

Seawater

Seawater

Seawater

Seawater

Natural water, tap water

CU

Cu, Ni

CU

Cd, Pb, Cu

Cu. Pb, Cd, Zn

River water, coastal water Lake water

Hg

Al

Model solutions of: Ciodo-benzoic acid, 2-iodo-benzoic acid, 3,5-diiodo-L-tyrosine, 3,5-diiodothyronine, iodo-acetic acid in artificial seawater, seawater Seawater

I

Seawater

Pb, Cd, Cu

cu

Estuarine water Cu. Zn, Fe Seawater Cr

Coastal water Sn

UV-lamp 100 W or 1000 W, t= 4 h, pH 2.2 UV-lamp 1200 W, t= 5 h,

PH 2 UV lamp high energy, t = 4 h, pH 4 UV-lamp 550 W, I = 6 h, pH natural UV-lamp immersion 35 W, t =5-6 h, pH natural, add.

Hz% UV-lamp, t = 24 h, pH 1

UV-lamp 450 W. t = 4 h, pH natural, add. H,O,, temp. 80°C UV-lamp 1000 W

CSV-HMDE [IO91

CSV-HMDE [1101

spectrophotometric, A = 434 11061 nm ASV-RGCE [lo41

ASV-RGCE [1051

flameless AAS

ET-AAS

11131

11141

spectrophotometric, A = 410 [ 1161 nm

UV-lamp 1200 W, r = 3 h,

PH 2 UV-lamp 1000 W, t > 5 h

pH 2.6 UV-lamp 100 W or 1000 W, r = 4 h, pH 7-8.5 Flow system UV-lamp, r = 20 min. pH < 1

DPASV-MFE f1111

spectophotometric. h = 434 [IO71

2Yk-SMDE [to81 CSV-HMDE [I121

FAAS [I151

t - time of UV irradiation, add. - addition of.... Method of determination: AAS - atomic absorption spectroscopy, ET-AAS - electrothermal atomization AAS, FAAS - flame AAS, ASV - anodic stripping vohammetry, DPASV - differential pulse anodic stripping voltammetry, CSV - cathodic stripping voltammetry.

Type of electrode: HMDE - hanging mercury drop electrode, SMDE - static mercury drop electrode, MFE - mercury film electrode. RGCE - rotating glassy carbon electrode.

126 J. Golimowski. K. Golimowskrr/Annlytica Chimica Acta 325 (1996) III-133

ceded by a separation unit, e.g. LC column [ 11.51 the method of CO, determination were investigated allows for rapid determination of different forms of [28,34,47], and comprehensive reviews of procedures the investigated element. In this technique AAS for the determination of TOC (including the UV- methods are used for determination. mineralization) were published [ 129,130].

The reviews of the problems concerning speciation of heavy metals in natural waters (including the application of UV irradiation) were presented by Florence and Batley [118] and by van den Berg [119].

The conditions of samples UV-photooxidation and the methods of speciation are presented in Table 3.

The application of UV-photooxidation in the determination of TOC in water and waste water has become so popular and well documented that it has been comprised in the international [ 13 13, german [132], american [133,134], and japanese [135] standards.

5.4. Nitrogen determination 5.3. Carbon determination

Determination of dissolved organic carbon (DOC) consists of its oxidation to CO,. The generated gas can directly be determined in an IR detector, e.g. [61,120,121] or it can be reduced to methane and then determined in a flame-ionisation detector, e.g. [120]. CO, can also be detected: gravimetrically [107], by spectrophotometric methods, e.g. [122- 1241, by potentiometric titration [ 1251, by conducto- metric methods, e.g. [40-421 or by more sophisti- cated methods like inductively coupled plasma- atomic emission spectrometry (ICP-AES) [ 1261, flame infrared emission (FIRE) [ 1271 and measurement of chemiluminescence [128]. The review of CO, detection methods was done by Robards et al. [129].

Armstrong et al. [52,130], as the first, used a stationary UV mineralizer for the oxidation of organic carbon dissolved in seawater. They used two mercury lamps with 1200 W and 380 W and obtained total oxidation of carbon after 1 and 11 h, respectively. Goulden and Brooksbank [61] devel- oped a system for an automatic DOC determination in natural water. The use of flow systems is now very popular for TOC determination, many commercial automatic analyzers contain the UV-unit, e.g. [42,121,123,124].

It was found that during UV irradiation and in the presence of oxygen, N-containing organic compounds and NH: ions are initially oxidised to nitrates and then slowly reduced by aromatic compounds to nitrites. As a result, the total amount of nitrogen in a sample is converted to nitrates and nitrites after the mineralization [52]. Nitrogen determination, therefore, means the determination of NO; and NO; ions or their sum. A popular method is the reduction of NO, ions to NO; ions in a flow system using activated cadmium [ 135,137], however, other activators especially EDTA and DTPA were also proposed [73]. The NO; ions are determined spectrophotometrically applying the Griess reaction. Nitrite reacts in an acidic medium with sulfanilamide and a-naphtbyl-ethylenediamine dihydrochloride to produce a coloured azo-compound. The absorbance of the formed compound is measured at 540 nm [45,136,137]. Other methods of determination of nitrogen in water are presented in a review by Robards et al. [129].

The application of UV-photooxidation in the determination of TOC in water and waste water has been studied for many years and now the number of papers concerned to this subject is very large. The influence of many parameters (temperature, irradiation time, lamp power, pH, addition and concentration of K, S,O,, H,O, and other catalysts) on the degree of decomposition of organic substance using

The choice of conditions for sample mineralization depends on the types of nitrogen compounds contained in a sample. Investigations based on syn- thetic solutions [45,51-53,130] indicated that the pH value of the digested sample is one of the most important factors deciding in the efficiency of the mineralization process. Most of the organic nitrogen compounds are decomposed at pH 7-9, whereas urea is decomposed at pH 4-6. The influence of pH value, irradiation time, persulfate concentration and total content of nitrogen in a sample on the effective- ness of nitrogen oxidation were studied [51,53,63].

Some authors recommend a two-step method of sample mineralization for nitrogen determination

J. Golimowski. K. Golimowska/Adytica Chimicu Acru 325 (1996) 111-133 127

Table 4 Application of UV-photooxidation in determination of nitrogen

Sample Conditions of photooxidation Concentration range of nitrogen, Reference

mdl _. Model solutions of: NH&l, 0.2 [521 UV-lamp 1200 W. t = 2-3 h,

add. H,O,, pH < 8 2,2’-bipyridine, casein, thiourea,

adenine, guanidine, pyridine,

seawater

Model solutions of: NH&l, for-

mamide, oxamic acid, oxamide,

urea, pyridine, m=carbamoyl as-

partate, L-citrulline, RNA, gela-

tine in distilled water,

seawater

Model solutions of: alanine, tryp

tophane, adenosine, thymine,

uracil, benzamide, DNA,

cytosine, diethylamine,

urea,

river water

Model solutions of: 2,2’-bipiry-

dyl, l,lO-phenantroline, EDTA,

NH&l, KNO,,

natural water Model solutions of: glycine,

trypthone, indol in distilled water and artificial seawater, lake wa-

ter

Model solutions of: glycine.

EDTA, %hydroxyquinoline, n-

butylamine, NH&l, urea,

gelatine, milk, pepsine, meat

peptone. caffeine, creatinine, 2,2’-bipixydyl, hexamethylenete-

tramine, uric acid, urea, p-

aminobenzoic acid in distilled

water and in artificial seawater Model solutions of: urea, (Y-

alanine, EDTA, histidine hydro- chloride in distilled water

Model solutions of: urea, glycine, EDTA, tn_-alanine, leucine, pyri-

dine, diphenylcarbazone, semi- carbazone, dinitrophenylhydra-

zine, 3-methyl-1-phenyl-2-

pyrazolin-5-one

Model solutions of: NH&

glycine, aspargine, glutamine,

alanine, lysine, betaine, urea, tri- ethanolamine, hydroxyl ammo-

nium-chloride, sulfanilamide,

N,N-dimethylformamide, EDTA, tributylamine, NaNO,, hydraz- inum sulfate, potassium thio- cyanate in water,

0.01 M CaCl,

UV-lamp 380 W, t = 12-24 h.

add. H,O,

UV-lamp 1000 W, t = 3 h, add.

H,O,. pH 9

pH 11

two-step photoox. (1) r = 2 h,

pH4;(2)t=3h,pH9

UV-lamp 900 W, I = 4 h, add.

H,O,, pH 6.5-9

immersion UV-lamp 450 W, t = 1.5-3 h, cont. oxygenation or

add. H,O,. pH 3.7-8.5

UV-lamp 900 W, f = 3 h, add.

H 20,, pH 7-9 (4-6 for urea)

two-step photoox. (1) t = I h,

pH 2.1, (H,SO,); (2) r=3 h, pH 8.5-9, add. H,O,

UV-lamp 36 W, t = 15 min. pH

6-7, 11.8-12.1, add. K,S,O,

continuous flow system, UV- lamp 1200 W, t= 17 min. pH

2.0 and 13.0

continuous flow system UV-lamp

14 W, t = 15 min, add. K,S,O,

0.03-O. 13

0.002-0.009

0.3-0.35

0.02-0.03

0.15-2

0.05-0.6

11301

[451

[531

[511

ca. 0.28

[I381

0.5-2.5

0.5- 1

2 i64.651

2-8 mg/lOO g soil

[551

[1391

128

Table 4 (continued)

J. Golimowski, K. Golimowsku/Anolytica Chimica Acta 325 (1996) Ill-133

Sample Conditions of photooxidation Concentration range of nitrogen, Reference

w/l Model solutions of: NH,CI, urea, flow-injection system, pH 8.5, I [721 glycine, aminobenzoic acid, add. K,S,O,

nicotinic acid, EDTA, oximic

acid, barbituric acid Model solutions of creatinine, flow-injection system UV-lamp l-50 Titriplex III, aspartic acid, hex- 50 W, t = 2 min. pH 9.5, add.

amethylentetramine, barbituric K,S,Os acid, cyanacetamide, hydrazine

sulfate, urea, NH&l, KNO,,

waste water

Model solutions of: (NH&SO,, continuous flow system UV-lamp O-30

glutamic acid, HMTA, urea, 8 W, pH 9, add. K,S,O,

nicotinic acid in deionized water,

surface water, 3-10

waste water IO-50 Model solutions of: trieth- flow system UV-lamp 10 W, 5

ylamine, hexamethylenete- t = 8 mm, add. K,S,O, tramine EDTA, sulfanilic acid,

(NH,),so,, pyridine, camho-

[621

1631

[I241

benzoic acid, chloramine T, urea,

tbiourea, waste water

t - time of UV-irradiation, add. - addition of....

In ref. [ 1391 nitrogen was determined as NH, [ 1471 by a selective electrode, in [62] by measurement of absorbance of NO; h = 226 nm, in all other cases by absorbance of the azo-compound in the range 520-540 nm.

[41,138]. In the first step, samples are UV-irradiated at lower pH (2-4), and in the second step at a higher pH (8.5-9). It was found that the two-step method gives always better efficiency of oxidation of nitrogen compounds (for urea even 36% better, caffeine 35%, proteins ca. IO%>. The efficiency equals 99.2% for urea and 94.2% for caffeine but 95.4% for the natural water samples. It was also pointed out, that the influence of the presence of organic substances, their salts (especially bromides in seawater), CO, and oxygen on efficiency of nitrates and nitrites formation in the photooxidation process, should be taken into consideration [138].

The automated systems with UV-unit are also used for nitrogen determination [64,65,139,140]. Flow-injection analysis was described for waste water [62] and for natural water [72,73]. UV-mineralization was also applied for the determination of nitrogen in soil extracts using an automatic analyser for nitrogen determinations [64,65].

The Kjeldahl mineralization method and the UV- mineralization method, for total nitrogen determina-

tions, were compared by many authors [53,63,65,72,138]. Henriksen [53] found that the mean difference between two sets of results was 5

PLg 1-l of nitrogen, in the concentration range of 0.15-2 mg I-’ (with the higher value obtained by a photooxidation method), the standard deviation of difference being 30 pg 1-l of nitrogen, thus giving a relative standard deviation of the difference between the two methods of 8.5%. Analysing samples of natural water in a similar concentration range, Gustaffson [138] obtained higher nitrogen concentration values using the Kjeldahl method; the difference being smaller than 8%. The comparison of the results of determination of total soluble nitrogen in soil extracts [65] with the results obtained in a Kjeldahl method did not show any significant difference. The comparison of flow-injection UV-photooxidation with Kjeldahl and alkaline persulfate batch methods was done by McKelvie et al. [72]. Good agreement was achieved for most samples of estuarine, marine, fresh and waste water samples over a wide range of concentrations and salinity conditions.

J. Golimowski, K. Golimowska/Analytica Chimica Acta 325 (1996) 111-133 129

Table 5 Application of UV-photooxidation in determination of phosphorus

Sample Conditions of photooxidation Concentration range of phospho- Reference

rus* I.Lg/l

Model solutions of RNA, p UV-lamp 1200 W, t = 1-2, add. ca. 100 b21 glycerophosphate, ribose-S-phos-

phate, choline phosphate, 2-

aminoethanphosphoric acid in ar-

tificial seawater,

seawater

Model solutions of: glucose-6

phosphate, AMP, RNA, triph-

enylphosphine, pyrophosphate in

distilled water and in seawater,

seawater Model solutions of: disodium

phenylphosphate, AMP, ADP,

ADTP, glycerol-2-phosphate,

flavine-mononucleotide dis-

odium salt, methyhriphenylphos-

phonium bromide, tris( ppro-

pionic acid) phosphonium chlo-

ride, natural water, waste water

Natural water containing iron

Model solution of DNA and

glycerophosphate, river water

Model solutions of: cytidine-5’- phosphate, deoxyguanosine-S-

phosphate in distilled water,

natural water

Model solutions of: phylic acid,

p glycerophosphate, a-r>glu-

case- 1 -phosphate, 2-aminoethyl- phosphonic acid, adenosine-

2’(3’)-phosphonic acid, trimeta- phosphate, pyrophosphate in

mili-Q-ultra pure water, soil ex-

tracts

Model solutions of: ortophos- phate, phytic acid, glucose-

6’ phosphate, 2-aminoethyl-

phosphate, ADP, phosphoenol- pyruvale, natural water, sewage

effluents, algal cuhure

Seawater

H202

two-step method: (1) UV-lamp

380 W, t = 5 h, add. H,O,; (2)

boiling with add. 0.025 M HCl,

t=l h

UV-lamp Zn-Cd-Hg 75 W, r =

30 mm, add. H,SO, + H,O,

UV-lamp 900 W, t = 1.5-2 h,

pH ca. 2, add. H,O, UV-lamp, t = 30 min

UV-lamp 36 W, t = 15 min. add. K,S,O, + H,SO,

flow system UV-lamp, add.

H,O, or K,S,O,

flow-injection UV-lamp 40 W,

add. K,S,O,

(1) UV-lamp 1200 W, r = 1-18

h, add. H,O,; (2) two-step method: UV-irradiation, K,S,O,

O-30

0.26-0.75

70-3700

4-240

ca. 150

20-180

300

30-140

5-100

100-4000

[1301

[I441

1531

[351

(551

[661

11451

0.6-12.4 [1461

autoclave

r - time of UV irradiation, add. - addition of...., AMP - adenosine-5’-monophosphate, ADP - adenosine-5’-diphosphate disodium salt, ATP - adenosine-5’-triphosphate disodium salt, ADTP - adenosine-5’-tetraphosphate triscdium salt.

130 J. Golimowski, K. Golimowska / Analytica Chimica Acta 325 (1996) 11 l-I33

UV-photooxidation methods have been criticised because they give poor recoveries for compounds containing N-N and N=N bonds. The comparison of batch UV-photooxidation and high temperature combustion (HTC) methods shows that the UV method gave a recovery of 60% compared with the HTC method for such compounds, and 90-95% for other compounds [141]. However, the UV method gave 98% recovery compared with the HTC method for seawater samples [72].

The conditions of UV-mineralization of various samples containing nitrogen are collected in Table 4.

5.5. Phosphorus determination

The phosphorus analysis consists of its transfor- mation into orthophosphate ions and subsequent determination in the form of molybdenum blue. In this method, ammonium molybdate reacts in an acidic medium with PO:-, potassium ammonium tartrate being a catalyst for this reaction. The complex compound formed is then reduced by ascorbic acid giving an intense blue solution. Its absorption is measured at 880 nm [ 142,143]. Organic-bound phosphorus is calculated from the difference before and after the mineralization. Other procedures for the determination of dissolved phosphorus are presented by Robards et al. 11291.

A mineralization of samples for subsequent determination of total phosphorus is usually conducted with an addition of oxidants like H,O, [52,53,66,130,144] or K,S,O, [55,66,145,146]. Both oxidants can be used in batch systems as well as in flow systems [66,145]. Samples are also acidified [53,55,144] by HCl or H,SO, to increase the mineralization and to avoid of formation of iron(II1) phosphate (in the case of presence of this metal in the sample), which is not detected by the applied method

[531. The most ‘recalcitrant’ phosphorus compounds

are polyphosphates. For the first time the presence of these compounds in seawater was detected by Arm- strong and Tjbbits [130]. To decompose this type of phosphates two-step procedures are proposed. In the first step the sample is W-irradiated, and in the second it is boiled in the medium of HCl [ 1301 or

K,S,O, [1461. A special treatment of soil extract samples is

necessary because of the presence of aluminium, which at the conditions of a digestion process, especially in flow system, can be deposited as AI(O on the wall of a reactor, adsorbing H,PO,. The subsequently determined phosphorus content is decreased by the amount bound with aluminium. To avoid this, fluoride ions forming strong complexes with aluminium and hindering the unwanted deposi- tion of AI(OH are introduced to the sample [66].

In various papers, the method of photooxidation of phosphorus compounds and the conventional method of oxidising with persulfate were compared. Analysing over 100 samples of natural water in the phosphorus concentration range of 4-240 pg l- ’ , Henriksen [53] did not find any significant difference. McKelvie et al. [ 1451, using W-mineralization in a flow injection system, achieved a good correla- tion with the persulfate method in the range of lo-400 ,ug 1-l. On the basis of phosphorus determination in river water samples (20-l 80 pg 1-l ), Semenov et al. [45] did not observe any significant differences when they compared a UV-mineralization method with a wet digestion in concentrated H,SO,. A detailed comparison between a W- mineralization with addition of potassium persulfate with the conventional method (the destruction by potassium persulfate in a medium of sulfuric acid) is given in the Application Bulletin of Skalar [67]. No significant differences were observed in the results obtained by both methods. The UV-method gave, however, better recoveries than the conventional method, in the range of lower concentrations ( < 100

fJg 1-l for trimethylphosphate as a standard substance). The conditions of UV-mineralization of various samples containing phosphorous are collected in Table 5.

6. Conclusion

The comparison of the wet digestion method with the W-digestion method indicates that the latter one can well replace the conventional methods. This is the case in the trace determination of heavy metals as well as in the determination of carbon, nitrogen and phosphorus. The destruction of some compounds, however, can be difficult and requires ex- treme mineralization conditions like long irradiation

J. Golimowski, K. Golimowska/Andytica Chimica Acta 325 (1996) Ill-133 131

time, the two-step mineralization combined with pH change (for urea decomposition) or the combination of UV irradiation with subsequent HCl or K,S,O, boiling (polyphosphate decomposition). But even if the decomposition was not complete, it would be worthwhile to use UV-mineralization due to the decreasing danger of sample contamination and ease of use. There is also no problem of the acid vapours evolving during wet digestion.

The descriptions dealing with UV-mineralization processes are not sufficiently detailed and they especially lack data related to the type of lamp used and its power. The present paper attempts to confront and arrange all knowledge necessary for an analytical chemist to choose proper mineralization conditions depending on sample type and determined elements.

Acknowledgements

This study was carried out with financial support of BST-502/7/95.

References

[ll

121

131

[41 151

bl

[71

[81 I91

t101

[I 11

[I21

[131

[I41 _ _

L.R. Koller, Ultraviolet Radiation, John Wiley, New York,

W.R. Haag and J. Hoignt, Environ. Sci. Technol., 20

1965, pp. 22, 236.

(1986) 341.

Symp. Pap.-Heraeus Instruments GmbH, Poznat?, 1990, Ap-

plication of UV sources to water disinfection and waste

water treatment. T. Vieweg and W. Thiemamr, Vom Wasser, 79 (1992) 355.

X. Zhou and K. Mopper, Mar. Chem., 30 (1990) 71. P.B. Merkel and D.R. Kearns, J. Am. Chem. Sot., 94

( 1972) 7244. R.G. Zepp, N.L. Wolfe, G.L. Baughmann and R.C. Hollis,

Nature, 267 (1977) 421.

H. Kautsky, Trans. Faraday Sot., 35 (1939) 216.

R.M. Baxter and J.H. Carey, Nature., 306 (1983) 575. T. Mill, D.G. Hendry and H. Richardson, Science, 207 (1989) 886.

R.G.W. Norrish, F.R.S. and R.P. Wayne, Proc. R. Sot. A,

288 (I%51 201.

M. Galbraith, M-M. Shu, S. Davies and S. Masten, Haz-

ardous Ind. Wastes, 24 (1992) 411.

K. Chelkowska, D. Grasso, I. Fabian and G. Gordon, Ozone Sci. Eng., 14 (1992) 33.

S.D. Killops, Water Res., 20 (1986) 153.

1151 E. Gilbert, Vom Wasser, 55 (1980) 1. [43] G.K. Korolev, A.A. Nazarova and V.B. Stradomski, 1161 E. Gilbert, Water Res., 22 (1988) 123. Gidrokhim. Mater., 84 (1983) 91.

1171 P.L. Yue, Symp. Pap.-Inst. Chem. Eng. Nort West Branch 1992, 3 (3 Integr. Pollut. Control Clean Technol., 15, l-15, 9). Chem. Abstr., 117 (1992) 156944.

1181 R. Barker, Electr. Count. Res. Cent [Meno] ECRC/M 1979, ECRC/M 1233 16 pp. Chem. Abstr., 91 (1979) 78549.

1191 H.W. Jr Prengle, Ch.E. Mauk and J.E. Payne, Proc. Forum Ozone Disinfect., 1976 (PubI. 19771, Chem. Abstr., 87

(1976) 141028.

]20] R.K. Arisman, R.C. Musick, R.C. Zeff and J.D. Craset, Proc. Ind. Waste Conf. 1980 (Publ. 1981), Chem. Abstr., 95 (1981) 29749.

1211 G.J. Macur, W.A. Alpaugh and J.E. Sharkhuss, Proc. hid. Waste Conf. 1980 (PubI. 1981). Chem. Abstr., 95 (1981) 29750.

[22] E. Leitis, J.D. Zeff and M.M. Smith, Chemistry and Appli-

cation of Ozone and Ozone/UV Light for Water Reuse

Report 1981, Westgate Res. Corp. West Los Angeles, Chem.

Abstr., 96 (1982) 91077.

]23] T. Niitsuma, K. Suzuki, E. Hachiya and Y. Takemoto,

Kankyo Kagaku 3 (1993) 350, Chem. Abstr., 119 (1993) 11264.

[24] S. Gudera, M. Machido, K. Yamao, T. Iwasaki, K. Nishikosi

and K. Arai, Kankyo Kagaku, 3 (1993) 262, Chem. Abstr., 119 (1993) 124711.

1251 W.R. Haag and J. Hoigne, Chemosphere, 14 (1985) 1659.

1261 D. Kotzias, H. Parlar and F. Korte, Naturwissenschaften, 69 ( 1982) 444.

1271 DC. Zatiriou, J. Geophys. Res., 79 (1974) 4491.

]28] M. Malaiyandi, M.H. Sadar, P. Lee and R. O’Grady, Water Res., 14(1980) 1131.

1291 M. Schmidt, K. Seikel, G. Bruckmann and M. Trager, W/B Wasser, Luft, Boden 37 (1993) 50.

[30] F.H. Frimmel, W.O. Fritsch and Ch.K. Scheck, Vom Wasser, 79 (1992) 101.

[3l] H. Kroder, K.-H. Bauer and D. Saur, Vom Wasser, 82 (1994) 269.

1351 B. Kraeutler and A.J. Bard, J. Am. Chem. Sot., 100 (1978) 5985.

]32] W. Dorten, P. Valenta and H.W. Nbmberg, Fresenius’ Z. Anal. Chem., 317 (1984) 264.

]33] D.A. House, Chem. Rev., 62 (1962) 185.

1341 R.A. van Steenderen and J.-S. Lin, Anal. Chem., 53 (1981) 2157.

]36] R.W. Matthews, Water Res., 20 (1986) 569.

]37] . C.K. Grlitzel, M. Jirousek and M. Gratzel, J. Mol. Catal., 39 (1987) 347.

1381 1. Izumi, W.W. Dunn, K.O. Willboum. F-R.F. Fan and A.J.

Bard, J. Phys. Chem., 84 (1980) 3207.

[39] R.W. Matthews, Aust. J. Chem., 40 (1987) 667.

t40] R.W. Matthews, J. Phys. Chem.. 91 (1987) 3328.

1411 R.W. Matthews, M. Abdullah and G.K.-C. Low, Anal. Chim. Acta, 233 (1990) 171.

]42] G.K.-C. LOW and R.W. Matthews, Anal. Chim. Acta, 231 (1990) 13.

132 J. Golimowski, K. Golimowska/Analytica Chimica Acta 325 (1996) III-133

[441 F. Frimmel and H.A. Winkler, Z. Wasser Abwasser Forsch., [75] J. Golimowski, A.G.A. Merks and P. Valenta, Sci. Total 8 (1975) 67. Environ., 92 (1990) 113.

[45] A.D. Semenov, B.G. Soyer, W.A. Bryzgalo and L.S. Kos-

menko, Zh. Anal. Khim., 31 (1976) 2030.

[461 T.N. lvanov and A.N. Antonov, Zh. Anal. Khim., 35 (1980)

588.

1761 P.A. Hustenko, E.A. Zaharova, E.E. Fominceva and J.A. lvanov, Zavod. Lab., 57 (1991) 1.

[77] J. Golimowski and A. Sikorska, Chem. Anal. Warsaw, 28 (19831411.

[47] P. BlaZka and L. Prochlzkova, Water Res., 17 (1983) 355.

[48] Handbook of Chemistry and Physics, 67th edn., CRC Press, Boca Raton, Florida, 1986-1987, p. 257.

[49] R. Phillips, Sources and Applications of Ultraviolet Radia- tion Academic Press, London, New York, 1983, pp. 179-

184, 193, 196.

1781 J. Golimowski, Anal. Lett., 22 (1989) 481.

1791 C.E. Stringer and M. Atttep, Anal. Chem., 51 (1979) 731.

1801 R.H. Atallah and D.A. Kalman, Talanta, 38 (1991) 167.

[81] A. Postupolski and J. Golimowski, Electroanal., 3 (1991) 793.

[501 A. Unkroth and U. Khmer, Fresenius’ J. Anal. Chem., 347

(1993) 464.

[51] B.A. Manny. M.C. Miller and R.G. Wetzel, Limnol.

Gceanogr., 16 (1971) 71.

[52] F.A.J. Armstrong, P.M. Williams and J.D.H. Strickland, Nature, 211 (1966) 481.

[82] Z. Jo&a, private communication.

[83] B. Pihlar, P. Valenta, J. Golimowski and H.W Nurnberg, Z. Wasser Abwasser Forsch., 13 (1980) 130.

[84] M. Kolb, P. Rach, J. Sch”afer and A. Wild, Fresenius’ J.

Anal. Chem., 344 (19921 283.

(851 SK. Bhowal, D. Saur and R. Neeb, Fresenius’ J. Anal. Chem., 346 (19931627.

[53] A. Henriksen, Analyst, 95 (1970) 601.

[54] L. Sipos, J. Golimowski, P. Valenta and H.W. Nbmberg, Fresenius’ Z. Anal. Chem., 298 (1979) 1.

[55] A.N. Shkil, A.B. Krasnushkin and I.T. Gavrilov, Zh. Anal.

Khim., 45 (1990) 1615.

[86] R. Breder and M.J. Schwuger, Dechema-Monographien Band 124VCH Verlagsgesellschaft. 1991, p. 149.

[87] R. Breder and G. Welp, Mitt. Dtsch. Bodenkundl. Gesellsch., 66(I) (1991) 279.

[56] G. Schwedt, Labor Praxis, July/August 1990. [57] J. Labuda, D. Saur and R. Neeb. Fresenius’ J. Anal. Chem.,

348 (1994) 312.

[58] G. Schwedt and J. Petri, Labor Praxis, December 1992,

1223.

[88] R. Breder and L. Mart, GIT Fachz. Lab. 6/1992, p. 637.

[89] J. Golimowski and T. Szczepatiska, 6th hit. H.W. Niimberg Memorial Symp. on Metal Compounds in Environment and

Life, 1995, B 31, p. 123, Fresenius’ J. Anal. Chem., in press.

[59] D. Saur and E. Spahn, GIT Fachz. Lab., 2/1994, p. 103.

[M)] M. Kolb, P. Rach, J. Schtier and A. Wild, Fresenius’ J. Anal. Chem., 342 (1992) 341.

[61] P.D. Goulden and P. Brooksbank, Anal. Chem., 47 (1975)

1943.

1901 J. Golimowski and A. Tykarska, Fresenius’ J. Anal. Chem., 349 ( 1994) 620.

[62] S. Hinkamp and G. Schwedt, Z. Wasser Abwasser Forsch..

24 (1991) 60.

[63] H. Kroon, Anal. Chim. Acta, 276 (19931 287. [64] P. Kutscha-Lissberg and F. Prillinger, Plant Soil, 64 (1982)

63.

[91] J. Golimowski, A. Orzechowska and A. Tykarska, Frese- nius’ J. Anal. Chem., 351 (19951 656.

[92] J. Golimowski, P. Valenta and H.W. Nllmberg. Z. Lebensm. Unters. Forsch., 168 (1979) 353.

1931 J. Golimowski, H.W. Nlmberg and P. Valenta, Lebensmit- telchemie u. gerichtl. Chemie, 34 (1980) 116.

[94] J. Pisch, J. Sch^aer and D. Frahne, GIT Fachz. Lab., 6/ 1993, p. 500.

[65] V.J.G. Houba, J. Novozamsky, J. Uittenbogaard and J.J. van der Lee, Landwirtsch. Forsch., 40 (19871 295.

[66] M.D. Ron Vaz, A.C. Edwards, CA. Shand and M. Cresser, Talanta, 39 (1992) 1479.

[95] J. Golimowski and 1. Gustavsson, Sci. Total. Environ., 31 (19831 89.

[96] J. Golimowski and K. Dmowski, Chem. Anal. Warsaw, 40

(19951 13.’

[67] Application Bulletin of Skalar Analytical B.V., Total (UV) Nitrogen and Total (UV) Phosphate Analysis, 1993.

[68] L. Plevier, Int. Lab., July 1994, p. 22.

[69] A.H.M.T. Scholten, P.L.M. Welling, V.A.Th. Brinkman and R.W. Frei, J. Chromatogr., 199 (1989) 239.

[70] G.E. Batley, Anal. Chem., 56 (1984) 2261. [71] J.A. Stiib M.J. Rozing, B. van Hattum, W.P. Coffmo and

V.A.Th. Brlnkmarm, J. Chromatogr., 609 (1992) 195. [72] I.D. McKeIvie, M. Mitri, B.T. Hart, I.C. Hamilton and A.D.

Stewart, Anal. Chim. Acta, 293 (19941 155.

[73] S. Motomizu and M. Sanda, Anal. Chim. Acta, 308 (1995) 406.

[97] International Standard IS0 5666/2-1983. Water quality - Determination of total mercury flameless atomic absorption spectrometry. Part 2. Method after pretreatment with ultra-

violet radiation.

[98] DIN-Norm 38406 Teil 16. Deutsche Einheitsverfahren zur Wasser-Abwasser und Schlammuntersuchung. Bestimmung

von 7 Metallen (Zn, Cd, Pb, Cu. Tl, Ni, Co) mittels Voltammetrie.

[74] J. Golimowski, P. Valenta and H.W. Nlimberg, Fresenius’ Z. Anal. Chem., 322 (19851 315.

1991 Polish Standard PN-91/C-04595/06, Water and Waste Water, Test for Lead, Determination of Lead by Voltamme-

[lOO] glish Standard PN-91/C-04560/04, Water and Waste Water, Test for Cadmium, Determination of Cadmium by

Voltammetry.

[loll Polish Standard PN-91/C-04596/05, Water and Waste

J. Golimowski. K. Golimowska /Analytica Chimica Acta 325 f 1996) I I I-133 133

Water, Test for Zinc, Determination of Zinc by Voltamme-

(1021 Relish Standard PN-91/C-04611/06, Water and Waste

Water, Test for Copper, Determination of Copper by

Voltammetry.

[103] G.E Batley and T.M. Florence, Anal. Lett., 9 (1976) 379.

[104] G.E Batley and T.M. Florence, Mar. Chem., 4 (1976) 347.

[105] T.M. Florence. Water Res., 11 (1977) 681.

[106] P.M. Williams, Limnol. Dceanogr. 14 (1969) 156.

11071 P. Foster and A.W Morris, Deep-Sea Res., 18 (1971) 231.

[108] C.M.G. van den Berg, A.G.A. Merks and E.K. Duursma, Estuarine Coast. Shelf Sci., 42 (1987) 785.

[109] M.A.L.M. Campos and C.M.G. van den Berg, Anal. Chim.

Acta. 284 (1994) 481.

[ 1 lo] J.R. Donat, K.A. Lao and K.W. Bruland, Anal. Chim. Acta.

284 (1994) 547.

[ I1 I] C. Capodaglio, G. Scarponi, G. Toscano, C. Barbante and

P. Cesson, Fresenius’ J. Anal. Chem., 351 (1995) 386.

[112] M. Boussemart, C.M.G. van den Berg and M. Ghaddaf,

Anal. Chim. Acta, 262 (1992) 103.

[113] W.F. Fitzgerald and W.B. Lyons, Nature, 242 (1973) 452.

[114] P.G.C. Campbell, M. Bisson, R. Bougie, A. Tessier and

J.-P. Villeneuve. Anal. Chem., 55 (1983) 2246.

[115] L. Ebdon, S.J. Hill and P. Jones, Talanta, 38 (1991) 607.

[I 161 V.W. Truesdale, Mar. Chem., 3 (1975) 111.

[117] J. Pempkowiak, Symp. Pap.-D&e k/Warszawy. 10-13.

Oct. 1989, p. 72. [l IS] T.M. Florence and G.M. Batley, Crit. Rev. Anal. Chem., 9

(1980) 219.

11191 C.M.C. van den Berg, in J.P. Riley (Ed.), Chemical Oceanography, Vol. 9, 1988, Academic Press, London, p.

197. 11201 R.A. van Steenderen, W.D. Basson, F.A. van Duuren,

Water Res., 13 (1979) 539.

[121] S.A. Huber and F.H. Frimmel, Anal. Chem., 63 (1991)

2122. [122] S. Motomizu, K. T&i, T. Kuvaki and M. Oshima, Anal.

Chem., 59 (1987) 2930.

[123] A. Aminot and B. Kerouel, Analysis, 18 (1990) 289. [124] J. Oleksy-Frenzel and M. Jekel, Anal. Chim. Acta, 1995, in

press. [125] W. Stefanska, A. Postupolski and S. Rubel, Chem. Anal.

Warsaw, 32 (1987) 919.

[126] R. Rohl and H.-J. Hoffman, Fresenius’ Z. Anal. Chem., 322

( 1985) 438.

[127] S.W. Kubala, D.C. Tilotta, M.A. Busch and K.W. Busch,

Anal. Chem., 61 (1989) 1841.

[128] T. Aoki, K. Ito and M. Munemori, Bunseki Kagaku, 37

(1988) 133.

[129] K. Robards, l.D. McKelvie, R.L. Benson, P.J. Worsfold,

N.J. Blundell and H. Casey, Anal. Chem. Acta, 287 (1994)

147.

[130] J. NamieSnik, Chem. Anal. Warsaw, 33 (1988) 853.

[131] International Standard IS0 8245-1987. Water quality -

Guideliness for the determination of total organic carbon

(TDC). [132] DIN Standard 38403-3. 1983. Deutsche Einheitsverfahren

zur Wasser-Abwasser- und Schlammuntersuchung -

Summarische Wirkungs- und StoffkenngrijDen (G~ppe H).

Bestimmung des gesamten organisch gebunden Kohlen-

stoffs (TGC) (H3).

[133] ASTM D 4779-93, Test method for total, organic and

inorganic carbon in high purity water by UV or persulfate

oxidation, or both and infrared detection.

[134] ASTM D 4839-88, Test method for total carbon and organic carbon in water by ultra-violet or persulfate oxidation, or

both and infrared detection.

11351 Japanese Industrial Standard, JIS K 055 l- 1988, Testing

methods for total organic carbon in highly purified water.

11361 E.D. Wood, F.A.J. Armstrong and F.A. Richards, J. Mar.

Biol. Assoc. UK, 47 (19671 23. [137] F. Nydhal, Talanta, 23 (1976) 349.

[138] L. Gustafsson, Talanta, 3 1 (1984) 979.

[139] J.H. Lowry and K.H. Mancy, Water Res., 12 (1978) 471.

[14O] J. Oleksy-Ftenzel and M. Jekel, Acta Hydrochim. Hydro-

hiol., 23 (1995) 212. [141] T.W. Walsh, Mar. Chem., 26 (1989) 2%.

[142] J. Murphy and J.P. Riley, Anal. Chim. Acta, 27 (1%2) 31.

[I431 T.G. Towns, Anal. Chem., 58 (1986) 223.

]144] J.T.H. Goosen and J.G. Kloosterboer, Anal. Chem., 50 ( 1978) 707.

11451 I.D. McKelvie, B.T Hart, T.J. Cardwell and R.W. Cattrall, Analyst, 114 (1989) 1459.

[146] J.J. Ridal and R.M. Moore, Mar. Chem., 29 (19%) 19.

(1471 J. Martens, P. van den Winkel and D.L. Massart, Anal. Chem., 47 (1975) 522.

uv-photooxidation as pretreatment step in inorganic analysis of environmental samples

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