atomic adsorption spectroscopy

7/28/2019 Atomic Adsorption Spectroscopy

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Objectives

The objective of this experiment is to determine the amount of cadmium and ferum contain in

plant tissue sample which is spinach by using AAS and ICP. On the other hand, this experiment handled

to apply the wet digestion method on sample preparation. Besides that, there also determination of the

amount of mercury in dried anchovies sample by using mercury analyzer.

ABSTRACT

Cadmium and ferum are one of heavy metal that is toxic that present in our environment. These

toxic substances may enter in plant tissue usually vegetables which we consume most every day. So, this

experiment is handled to determine the amount of cadmium and ferum contain in plant tissue. Take

note that this sample is prepared by using wet digestion method. Then, the AAS (atomic absorption

spectroscopy) instrument is used in order to help the determination of amount of both cadmium and

ferum. The instrument was used in uitm laboratory is Perkin Elmer.

The aim of this experiment is to determine the weight percentage of the cadmium and ferum in

the sample of plants. The plant was used is Spinach. This sample was analyzed by atomic absorption

spectroscopy. Standard that was used in this experiment is ferum and cadmium. The result that i get

from AAS experiment is , weight percent of ferum in sample = 6.29 10-3 % and cadmium = 1.75 10-3

%. In ICP on the other hand, weight percent of ferum in sample = 9.8938 x 10-2 % and cadmium = 3.9575

x 10-2 %.

For the mercury experiment, the amount of mercury detected in sample 1 = 8.50 10-5 g,

sample 2 = 2.35 10-4 g and sample 3 = 2.63 10-4 g


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INTRODUCTION

Atomic spectroscopy is the determination of elemental composition by its electromagnetic or

mass spectrum. The study of the electromagnetic spectrum of elements is called Optical Atomic

Spectroscopy. Electrons exist in energy levels within an atom. These levels have well defined energies

and electrons moving between them must absorb or emit energy equal to the difference between them.

In optical spectroscopy, the energy absorbed to move an electron to a more energetic level and

the energy emitted as the electron moves to a less energetic energy level is in the form of a photon. The

wavelength of the emitted radiant energy is directly related to the electronic transition which has

occurred. Since every element has a unique electronic structure, the wavelength of light emitted is a

unique property of each individual element. As the orbital configuration of a large atom may be

complex, there are many electronic transitions which can occur, each transition resulting in the emission

of a characteristic wavelength of light.

The science of atomic spectroscopy has yielded three techniques for analytical use

1. Atomic Absorption.2. Atomic Emission.3. Atomic Fluorescence.


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The process of excitation and decay to the ground state is involved in all three fields of atomic

spectroscopy. Either the energy absorbed in the excitation process, or the energy emitted in the decay

process is measured and used for analytical purposes.

Energy Transition

Atomic Absorption Spectroscopy

In atomic emission, a sample is subjected to a high energy, thermal environment in order to

produce excited state atoms, capable of emitting light. The energy source can be anelectrical arc, a

flame, or more recently, a plasma. The emission spectrum of an element exposed to such an energy

source consists of a collection of the allowable emission wavelengths, commonly called emission lines,

because of the discrete nature of the emitted wavelengths. This emission spectrum can be used as a

unique characteristic for qualitative identification of the element. Atomic emission using electrical arcs

has been widely used in qualitative analysis.

Emission techniques can also be used to determine how much of an element is present in a

sample. For a "quantitative" analysis, the intensity of light emitted at the wavelength of the element to

be determined is measured. The emission intensity at this wavelength will be greater as the number of

atoms of the analyte element increases. The technique of flame photometry is an application of atomic

emission for quantitative analysis.


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Cadmium is well known to be one of the most toxic heavy elements for animals. It has recently

become a serious problem that rice grains contain cadmium in some area of Japan. On the other hand,

some types of plants can grow in contaminated soils and absorb a large amount of cadmium in their

bodies. Such hyperaccumulator plants are expected to be used for remediation of environments.

However, the accumulation mechanism has not yet been revealed, with the elemental distribution of

cadmium and transportation during uptake remaining unclear.

Cadmium appear as a cause in thyroid disease, it is a very unique mineral. It is extremely toxic

and has toxic biological effects at concentrations smaller than almost any commonly found mineral. An

environmental poison found in water, on our food and in the air. It is found in processed grains, dairy

products, meats, fish, fertilizers, auto exhaust, cigarette smoke, batteries, solder and dentures. It

disrupts the absorption of other minerals and tends to settle in the heart and right kidney and affects

proper functioning of several enzymes.

Where as for Ferum, taken in the right quantity, it has immense health benefits. It is available in

extremely low quantities in animal and plant tissues which is why it is called a trace metal. Iron can be

found in meat, whole meal products, potatoes and vegetables. The human body absorbs iron in animal

products faster than iron in plant products. Iron is an essential part of hemoglobin; the red colouring

agent of the blood that transports oxygen through our bodies.

Iron may cause conjunctivitis, choroiditis, and retinitis if it contacts and remains in the tissues.

Chronic inhalation of excessive concentrations of iron oxide fumes or dusts may result in development

of a benign pneumoconiosis, called siderosis, which is observable as an x-ray change. No physical

impairment of lung function has been associated with siderosis. Inhalation of excessive concentrations

of iron oxide may enhance the risk of lung cancer development in workers exposed to pulmonary

carcinogens.

A more common problem for humans is iron deficency, which leads to anaemia. A man needs an

average daily intake 7 mg of iron and a woman 11 mg. A normal diet will generally provided all that is

needed.


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PROCEDURE

Determination of Ferum and Cadmium in Spinach Vegetable sample by using AAS.

Sample Preparation

1. First sample was cut into small and was dried in oven at 110 C for 24 hours.2. Then, sample was weighed about 3.0 g and divided into three small conical flasks.3. Then, 10ml of concentrate nitric acid, HNO3 was added into the sample.4. The steps are repeated twice in other two conical flasks.5. And samples were stood overnight.6. All the samples then were heated until the production of red nitrogen dioxide (NO2) fumes has

ceased.

7. After that the samples were cooled before added 1mL hydrogen peroxide, H2O2 solution.8. Then samples were continued heating and allowed them to evaporate to small volume.9. Next, samples were cooled before filter into 250ml volumetric flask.10.10 mL of the aliquot was taken and transferred into 10 of 50 mL volumetric flask.

Standard Solution Preparation

1. 10 ppm of cadmium was pipetted 2ml, 4ml, 6ml, 8ml and 10ml and transferred to 100ml ofvolumetric flasks.

2. The 100ppm of ferum was then pipette 0.5ml, 0.75ml, 1.0ml, 1.5ml and 1.75ml and transferredto 50ml of volumetric flask. All volumetric flasks were toped up with 10ml of sample mixture.

3. The mixture was diluted with the deionized water until reached the mark.


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Analysis

The series ofCadmium and Ferum standards were prepared and standard solutions in range

0.2ppm to 1.0ppm and 1ppm to 3ppm were prepared respectively. 10ml of sample then were added

into each standard solutions and mark up with distilled water.

This method known as standard-addition method. All standard solutions with sample were

analyzed using atomic absorption spectroscopy instrument. The absorbance of the standard solutions

with sample was recorded and linear calibration absorbance versus concentration was plotted. Amount

and percentage weight of cadmium and ferum in sample was calculated.


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Determination of Mercury in animal tissue by using Hg analyzer.

Sample Preparation

i) (Wet digestion)

1. Firstly, the anchovy sample was dried overnight about 24 hours.2. After that, 1 to 2 g was weighed of the dried anchovy samples and was doing for triplicate

samples.

3. Next, 9 ml of concentrated HNO3 was added into every sample and was allowed to standovernight.

4. The samples were heated until red color of NO2 was produced. After that, it was cooled andadded with 1 ml of 30% H2O2.

5. The solution was heated again and was allowed to evaporate to a small volume.6. Next, the samples were transferred through ashless filter paper into 50 ml volumetric flask and

mark up with distilled water. Finaly, the solution was pipette 10 ml into fraction vessel and 1

drop of KMNO4 was added into the solution.

ii) (Dilution step)

1. Sample 1, 2 and 3 were pipette 2.0, 2.5 and 3.0 ml respectively.2. Next the sample was transferred into 100 ml volumetric flask and was diluted with

distilled water until mark.


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Preparation of Mercury Standard

1. 1 ppm of mercury solution was prepared by dilute 10mL of 10 ppm of mercury solution in100mL volumetric flask and mark up with distilled water.

2. Standard solutions 0, 5, 10, 15, 20 and 25 ppb were prepared.

Preparation of NaBH4 in NaOH

1. 1.0 g of NaBH4 was weighed and was diluted with distilled water.2. Next, 0.25 g of NaOH was weighed and was diluted with distilled water.3. NaOH solution then transferred into 500 ml volumetric flask and it was put about quarter of the

flask.

4. Then the solution of NaOH was diluted with NaBH4 to the mark and the mixture was shakinggently.

Preparation of 3% Sodium Hydroxide

15 mL of 3% HCl was dilute with distilled water in 500 ml volumetric flask.


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RESULTS

Table of determination of Ferum and Cadmium in spinach sample by using AAS.

Metal Concentration

from the graph

Weight (g) Percentage (w/w)

in the sample

Ferum (Fe) 3.8 ppm 0.19 10-3

6.29 10-3

%

Cadmium (Cd) 1.06 ppm

0.053 10-3

1.75 10-3

%

Table of statistic evaluation

Metal Standard deviation Relative Standard deviation

Ferum (Fe) 1.080 64.79 %

Cadmium (Cd) 0.3742 74.84 %

Table of determination of Chromium and Cadmium in spinachsample by using ICP.

Metal Concentration (ppm) Amount (g) w/w %

Ferum (Fe) 1.2

9.8938 x 10

-2%

Cadmium (Cd) 0.48 3.9575 x 10-2

%


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Table of determination of Mercury in animal tissue by using Hg analyzer.

Sample Absorbance Concentration

(ppm)

Weight (g) Percentage of weight

(%)

1 0.0236 1.70 8.50 10-5 0.016

2 0.0686 4.70

2.35 10-4

0.041

3 0.0766 5.25

2.63 10-4

0.052

Table of Statistical Data of Sample

Mean, x Standard deviation,s

Relative standard deviation

(%)

1.9417 x 10-4

9.5598 10-5

49.23


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DISCUSSION

In this experiment the techniques was used to detect Cadmium and Ferum contained in plant

tissue is Atomic Absorption spectroscopy. It is is a technique for determining the concentration of a

particular metal element in a sample. It is also can be used to analyze the concentration of over 62different metals in a solution. It is more sensitive because it could detect the concentration of analyte up

to ppb value and it also provide a high precision throughout the process.

From the results, the concentration of both the Cadmium and Ferum is tabulated in a table form

so that it can be observed clearly. Based on the table, it shows that the concentration of Cadmium is

smaller than Ferum. The concentration of Cadmium = 1.06 ppm and Ferum = 3.8 ppm. Basically, it can

be directly obtained by the graph plotted. The calibration graph absorbance versus concentration of

sample added was plotted by using Least Square Method. Thus, the straight line can be obtained andthe trace metal concentration in samples is given by the intercept of the curve on the x-axis.

In this experiment, the amount of Ferum and Cadmium is known which is 0.1910-3 g and

0.05310-3

g. Other than that the percentage ofFerum and Cadmium in Spinach are 6.29 10-3

% and

1.75 10-3 % respectively.

By comparing the concentration of the Ferum and Cadmium result in ICP, the concentration of

both of them in ICP are 1.2 ppm and 0.48 ppm respectively. So it is obvious the concentration obtained

using AAS is much higher than concentration obtained using ICP.

In mercury experiment on the other hand, the determination of mercury sample is by using

microwave dissolution method by Atomic Absorption Spectroscopy (FIMS 400, mercury analysis system).

Sample was prepared by wet digestion. Acid digestion procedure required to eliminates elemental loss

by volatilization because digestion takes place at a low temperature. But, this method subjected to

reagent contamination and tedious requires operator attention. The weight of sample used usually in

small amount only. If too much sample is used in wet digestion, the reaction mixture can become

violent. The amount of mercury in anchovys sample was achieved by plotting calibration curve

absorbance versus concentration (ppb).


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According to Beers law, concentration is proportional to absorbance. The amount of absorbance

from the sample can be used to find the concentration of the mercury in the anchovys sample.

Concentration that obtained from graph were multiple with dilution factor in order to obtained actual

concentration of mercury in sample. The percentage weight also was calculated and can be refer to the

table of result before.

In this analysis, the mean weight of mercury obtained from anchovys sample is 1.94 x 10-4 g.

The loss of mercury might be happen during preparation of sample and analysis time. So, some

precaution steps must be considered in order to get more precise result. From this analysis, it is found

that this anchovys sample has lower content of mercury and showed less health effects to human

behaviour. So, it is suggested to consume this type of anchovys due to low mercury content.


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CONCLUSION

The percentage of Ferum = 6.29 10-3

% and Cadmium = 1.75 10-3

% was detected in the plant

tissue (Spinanch). By using the ICP method, percentage of Ferum = 9.8938 x 10-2 % and Cadmium =

3.9575 x 10

-2

%. The AAS method was said to be more precise and accurate.So we can conclude that,the Cadmium and Ferum was successfully determined and it is present in the plant tissue (Spinanch).

For mercury experiment, the microwave dissolution methods was used in this experiment

involves treatment of the sample by wet digestion was concluded to be suitable for the determination

of mercury in anchovy samples. The amount of mercury in sample 1 = 8.50 10-5

g, sample 2 = 2.35

10-4 g and sample 3 = 2.63 10-4 g. So,the experiment is successfully achieved by us.

References

1. Spectroscopic Techniques Laboratory Manual CHM580. Pusat Pengajian Sains Kimia DanPersekitaran Fakulti Sains Gunaan Universiti Teknologi Mara, Shah Alam.

2. http://www.webmd.com/diet/features/top-10-iron-rich-foods3. http://www.lenntech.com/periodic/elements/fe.htm4. http://www.answers.com/topic/microwave digestion5. Skoog. D.A., Holler. F.J., Nieman T.A., Principle of Instrumental Analysis, Brooks/cole, 5th

ed., 1998.


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atomic adsorption spectroscopy

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