ANALYTICAL CHEMISTRY(CLD 10402)

Atomic Absorption Spectroscopy

Determination of Cooper (Cu) in AAS

PREPARED BY:

NAME: MUHAMMAD FADHIL BIN ABU BAKAR

ID NUMBER: 55103208065

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TITLE:- Determination of Cooper (CU) by using of the Atomic

Absorption Spectroscopy.

ABSTRACT:-The elemental analysis Atomic Absorption Spectroscopy which is

widely used in analyzing environment, metal, food, pharmaceutical and

chemical industries samples. In this experiment, the Atomic Absorption

Spectroscopy performance (sensitivity) is checked. The amount of

copper in sample standard solution is determined. Firstly, standard

solution of copper is prepared, with acid nitric. Next the instrument is

operated, by optimizing the Burner System and then the Performance

is checked and lastly Calibration curve is created and samples are

analyzed. Then graph of absorbance against concentration was plotted

to show the Beer’s Lambert Law.

OBJECTIVE:-To optimize the burner system by flame atomic absorption spectroscopy using standard solution.To check the performance (sensitivity) of the atomic absorption spectroscopy using standard solution.To prepare a serial dilution and generate a standard calibration Curve.To determine amount of cooper in the sample.

INTRODUCTION:-Atomic absorption methods measure the amount of energy (in the form of photons of light, and thus a change in the wavelength) absorbed by the sample. Specifically, a detector measures the wavelengths of light transmitted by the sample (the "after" wavelengths), and compares them to the wavelengths, which originally passed through the sample (the "before" wavelengths). A signal

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processor then integrates the changes in wavelength, which appear in the readout as peaks of energy absorption at discrete wavelengths.

The process of atomic absorption spectroscopy (AAS) involves two steps:

1.      Atomization of the sample2.      The absorption of radiation from a light source by the free

atoms

Figure below is the schematic diagram of atomic absorption spectrometer. Hollow cathode lamp will emit the line spectrum of the element to be analyzed. Samples are then atomized in the flame. Selection of wavelength of interest done by the monochromator.

In order to tell how much of a known element is present in a sample, one must first establish a basis for comparison using known quantities. It can be done producing a calibration curve. For this process, a known wavelength is selected, and

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the detector will measure only the energy emitted at that wavelength. However, as the concentration of the target atom in the sample increases, absorption will also increase proportionally. Thus, one runs a series of known concentrations of some compound, and records the corresponding degree of absorbance, which is an inverse percentage of light transmitted. A straight line can then be drawn between all of the known points. From this line, one can then extrapolate the concentration of the substance under investigation from its absorbance. The use of special light sources and specific wavelength selection allows the quantitative determination of individual components of a multi element mixture.

In this experiment, the ideal setup element used is coopers which have a wavelength at 324.8 nm and aspiration of solution of 4.0mg/L should produce of 0.200 absorbance.

Characteristic concentration is the concentration of analyte that gives 1% absorption or 0.0044 absorbance (as shown in checking the Performance part). Characteristic concentration is very useful in assessing instrument performance by showing a low characteristic concentration value which indicates a higher sensitivity.

AAS EQUIPMENT

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APPARATUS:-

► Perkin Elmer Atomic Absorption Spectrometer model 100 AAnalyst.

► Copper hollow cathode lamp.► Eight 100 ml volumetric flask.► Beakers► Pipette (2 ml and 5 ml)

CHEMICAL SUPPLIED:-

► 100 ppm Cooper (Cu) standard solution.► Concentrated nitric acid.► Distilled water.

Caution: Dispose all the chemicals in the proper waste container.

EXPERIMENTAL PROCEDURES:-

A. Preparation of cooper standard solution.

1) 10ml of 100ppm Cooper standard solution was poured into a small beaker and 10ppm Cooper standard solution been prepared in 100ml volumetric flask using the following equation;

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M1V¿ 1 ¿¿¿ = M2 V2

Where; M1 = Initial concentration in ppm

V1 = Initial volume in ml (volume of solution required)

M2 = Final concentration in ppm

V2 = Final volume in ml (volume of volumetric flask used)

2) I% (v/v) of concentration nitric acid (1% = 1ml) was added into the 100ml volumetric flask and deionized water was marked up to the volume.

WARNING!!!! Concentrated nitric acid is highly corrosive!! Please use glove for protection when you are dealing with the corrosive chemicals!!

3) 2.0 And 4.0 ppm of cooper standard solution is prepared from freshly prepared 100ppm standard solution using 100ml volumetric flask.

4) 0.5ppm, 1.0ppm, 1,5ppm, 2.0ppm and 2.5ppm cooper standard solution was prepared using 100ppm Zinc standard solution. 1% v/v of concentration nitric acid been added to each of the standard solution and the volume was marked up.

5) The standard solution prepared and ready to be analyzed.

OPERATING THE INSTRUMENT:- Please refer to the Appendix Step 1 until 5 and then do the following order as below;

1. Optimizing the Burner System.

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a) A blank solution was prepared.b) The known standard was aspirated using 8ppm.c) The burner position been adjusted using the

Horizontal adjustment knob and the nebulizer adjustment nut until a maximum absorbance is displayed on the screen.

d) The absorbance of blank was checked and it should be zero.

2.Checking the Performance.

a)Characteristic Concentration was clicked in the Analysis menu.

b)The sample concentration and instrument reading (the maximum absorbance) were entered.

c) The Tab key been pressed.d)The Measured Characteristic Concentration

should be within 20% of the Comparison Characteristic Concentration value.

e)Characteristic Concentration window was closed. The characteristic concentration value can also be calculated using the following equation;

0.0044 X known conc. Used

Characteristic Conc. Value = Absorbance for known conc. used

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3. Creating a Calibration Curve and Analyzing Samples.

a. Creating a calibration curve.i. The nebulizer tube was immersing into

blank solution.ii. The calibration standard was selected to

analyze from the dropdown list. The software completes the concentration entry according to the value entered in the method.

iii. Analyze Standard was clicked. This step been repeated for every calibration solution; 0.5ppm, 1.0ppm, 1.5ppm, 2.0ppm and 2.5ppm.

iv.The calibration curve been checked. If any of the standards appear to be off the

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calibration curve, then you may wish to edit the calibration curve.

b. Analyzing the samples.i. The nebulizer tube was immersed into

sample solution.ii. Analyze Samples been clicked.

4. Shut down the instrument by following step 7 in the Appendix.

REPORT SHEET:-

Stock Diluted

Concentration of Cooper

(ppm) M 1

Volume of Cooper (ml)

V 1

Concentration of Cooper (ppm)M 2

Volumetric flask (ml)

V 2

1 100 V 1=0. 5(100 )100

=0 .5 0.5 100

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2 100 V 1=1 . 0(100 )100

=1 .0 1.0 100

3 100 V 1=1 . 5(100)100

=1 .5 1.5 100

4 100 V 1=2 . 0(100 )100

=2.0 2.0 100

5 100 V 1=2 . 5(100)100

=2 .5 2.5 100

The calculation is using this formula:-M 1V 1=M 2V 2

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INSTRUMENT PARAMETERS:-

Blank solution 0.000Standard solution concentration (ppm) Absorbance (mean)

0.5 0.0061.0 0.0101.5 0.0162.0 0.0212.5 0.025

Unknown 1 0.040Unknown 2 0.006

Comparison characteristic concentration value (2ppm) = 0.077 mg/L.Measured characteristic concentration value (2ppm) = 0.303 mg/LComparison characteristic concentration value (4ppm) = 0.077 mg/lMeasured characteristic concentration value (4ppm) = 0.352 mg/l

% RSD (mean) = 0.4472Correlation coefficient (final) = 0.99786

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DISCUSSION:-

The amount of sample to be take for serial dilution was calculated as in the table below

Stock Diluted

Concentration of Cooper

(ppm) M 1

Volume of Cooper (ml)

V 1

Concentration of Cooper (ppm)M 2

Volume of

Cooper (ml)V 2

100 V 1=0. 5(100 )100

=0 .5 0.5 100

100 V 1=1 . 0(100 )100

=1 .0 1.0 100

100 V 1=1 . 5(100)100

=1 .5 1.5 100

100 V 1=2 . 0(100 )100

=2.0 2.0 100

100 V 1=2 . 5(100)100

=2 .5 2.5 100

The experiments were using 5 different concentrations which are 0.5ppm, 1.0ppm, 1.5 ppm, 2.0 ppm, 2.5 ppm. And the result is following 0.5 ml/ 0.5 ppm, 1.0 ml/ 1.0ppm, 1.5

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ml/1.5 ppm, 2.0 ml/ 2.0 ppm, and 2.5 ml/2.5ppm. The Atomic Absorption Spectrometer was using the flame technique which is the sample towards the small tube and burn with flame to get the absorption of the sample that tested.

The standard calibration was shown in the table below

Standard Calibration Graph for the Cooper

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Concentration (ppm) Absorbance

0.5 0.006

1.0 0.010

1.5 0.016

2.0 0.021

2.5 0.025

y = 0.0101x + 0.0004

R2 = 0.9967

0

0.005

0.01

0.015

0.02

0.025

0.03

0 1 2 3

Concentration

Absorbance

Series1

Linear(Series1)

Concentration of Unknown1:

Y=mx+c0.040 = 0.0101(x) + 0.0004X= 3.9207ppm

Concentration of Unknown 2:

Y=mx+c0.006= 0.0101(x) + 0.0004X= 0.5545ppm

CONCLUSION:-

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As the final result the absorption measurement follow the Beer’s-Lambert Law. The absorbance is directly proportional to the path length and the concentration of atomic vapor in the flame. From the experiment that had done the result for volume for the serial dilution are using the formula. The volumes are calculated from the concentration which is 0.5ml/ 0.5ppm, 1.0ml/ 1.0ppm, 1.5ml/ 1.5ppm, 2.0ml/2.0ppm and 2.5/ 2.5ppm cooper stock. Wavelength scan are used to determine at what the wavelength the cooper able to absorb. The result for the wavelength is 324.8nm. The standard calibration graph was determining the absorbance towards the concentration given. From the experiment the R2 is 0.4472 . Besides, the % RSD (mean) is 0.676 and correlation coefficient (final) is 0.9978. The concentration of unknown 1 is 3.9207 ppm and concentration of unknown 2 is 0.5545ppm and it absorbance is 0.006.

REFERENCE:-

www.weather.nmsu.edu www.answer.com www.wikipidea.com Raymond Chang., General Chemistry, McGraw-Hill International

Edition, p142 & p507.

APPENDIX:-

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Pre Laboratory Question:

1. What is the function of monochromator?

- Function of monochromator is to isolate analytical lines'

photons passing through the flame. Remove scattered

light of other wavelengths from the flame. In doing this,

only a narrow spectral line impinges on the PMT.

2. You are given a 100 ppm mercury stock solution. What is the volume needed in ml to prepare a 15 ppm standard stock solution in 50 ml volumetric flask? M1V1 = M2V2 100(V1) = 15(50) 100 V1 = 750 V1 = 7.5 ml.

Volume needed to prepare 15 ppm :15ml-7.5ml= 7.5 ml need to add to 100 ppm solution to make 15

ppm solution in 50ml volumetric flask.

3. How would you determine the performance of atomic absorption spectrometer?

. The measured characteristic concentration should be within 20% of the

comparison characteristic concentration value or

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calculated using the

following equation;

Characteristic = 0.0044 x known conc. usedConc. Value Absorbance for known Conc. used

4. Calculate the characteristic concentration value for 2ppm cooper standard that has absorbance value of 0.194 absorbance.

Characteristic Con. Value = (0.0044) X (known conc. used) Absorbance for known conc. Used

= (0.0044) X (2 ppm)

0.194

= 0.0454

Post Laboratory Questions

1. Ignator

2. Burner head

3. Nebulizer adjusting nut

4. Vertical adjustment knob

5. Horizontal adjustment knob

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