Atomic Absorption Spectroscopy

Its all about absorption & emission of radiation by specific element present in the sample.
We can calculate Absorption in terms of Transmittence by Beer's Lambert law.
A= 2-log(%T) or A= log(transmittance)

1. ATOMIC ABSORPTION SPECTROMETER BCH-503

2. ATOMIC ABSORPTION SPECTROMETER Introduction Invention Working Principle of AAS Instrumentation Interferences & Correlation Methods Applications

3. INTRODUCTION Atomic absorption spectroscopy  ( AAS ) is a spectroanalytical procedure for the quantitative determination of chemical elements using the absorption of optical radiation (light) by free atoms in the gaseous state. In analytical chemistry the technique is used for determining the concentration of a particular element (the analyte) in a sample to be analyze

4. INVENTION Introduced in 1955 by Alan Walsh in Australia Firstly used for mining , medical treatment & agriculture Alan Walsh(1916-1998)  At the Commonwealth Scientific and Industrial Research Organisation  (CSIRO) Solid & Solutions

5. Atomic absorption spectroscopy is based on the same principle as the flame test used in qualitative analysis.

6. The high temperature of the flame excites a valence electron to a higher-energy orbital. The atom then emits energy in the form of light as the electron falls back into the lower energy orbital (ground state). The intensity of the absorbed light is proportional to the concentration of the element in the flame.

7. quantitative analysis Atomic Spectra

8. PROPERTIES OF AAS The most widely used method in analysis of elements Based on the absorption of radiation So sensitive ( ppb ) Quantitative analysis

9. WORKING PRINCIPLE OF AAS Electrons promote to higher orbitals for a short amount of time by absorbing a energy M + hv → M * Relises on Beer -Lambert Law

10. Each element has a characteristic spectrum. Example: Na gives a characteristic line at 589 nm. Atomic spectra feature sharp bands. There is little overlap between the spectral lines of different elements.

11. Atomic absorption spectroscopy and atomic emission spectroscopy are used to determine the concentration of an element in solution.

12. INSTRUMENTATION

13. LIGHT SOURCES Hollow Cathode Lamps Anot-Tungsten wire Cathode made from the element of interest ( Na ,K, Ca ..) Argon or neon gas

14. LIGHT SOURCES Electrodeless Discharge Lamp Typically argon gas at low pressure Narrower line width Not prefered www. freepatentsonline .com

15. ATOMIZATION Compounds making up the sample are broken into free atoms . High temperature is necessary Basic two types - Flame atomizer ( air-acetylene flame) - Electrothermal atomizer

16. Process in a Flame AA M* M + + e _ M o M * MA M o + A o Solid Solution Ionization Excitation Atomization Vaporization

17. TYPES OF ATOMIZERS FLAME ATOMIZER Simplest atomization Converts analyte into free atoms of vapor phase ( Pnumatic Nabulizer+Aerosol ) Flammable & caustic gases Not has an inert medium ( −) Short analysis time ( − )

18. TYPES OF ATOMIZERS ELECTROTHERMAL ATOMIZER A cylindirical graphite tube atomizer 20–25 mm in length and 5–6 mm inner diameter Developed at St.Petersburg Russia Liquid(typically 10–50  μL ) or a solid (1 mg) Drying – solvent is evaporated;  Pyrolysis – matrix constituents are removed Atomization – analyte element is released to the gaseous phase Cleaning –high temperature. Tubes may be heated transversely or longitudinally Resistivity is noted

19. MONOCHROMATOR Also it is called wavelengh selector Select the specific wavelenght Polychromatic light → monochromatic light Simple one is enough for AAS

20. DETECTOR Electromagnetic waves → electric current The most used one Photomultiplier tube Have fast response times

21. CALIBRATION TECHNIQUES Two main techniques Calibration c urve method Standart addition method

22. CALIBRATION TECHNIQUES CALIBRATION CURVE METHOD Draw a graph Have two or more variables - One is set at known values - O ne is measured response Most convenient for a large number of similar samples analysis .

23. CALIBRATION TECHNIQUES An example of calibration curve method Y= bx+a

24. CALIBRATION TECHNIQUES STANDART ADDITION METHOD T o measu re the analyte concentration in a complex matrix. Most convenient for small number of samples analysis Prevent effect of chemical & spectral interferences

25. INTERFERENCES Causes higher or lower absorbance value Two major groups Chemical Interferences Spectral Interferences

26. CHEMICAL INTERFERENCES The most common one in flame atomizer. Consequence of chemical reactions . Reduce amount of oxygen in flame to overcome

27. SPECTRAL INTERFERENCES Absorption or emission of the radiation at the same wavelength Radiation which is absorbed → pozitive errors Radiation which is emmitted → negative errors

28. Atomic Absorption Overview

29. CONCLUSION One of the most important technique in quantitative analysis It is based on the absorption of radiation Measurements could be done at ppb levels It’s widely used method The preparation of the sample is usually simple and rapid

30. CONCLUSION There are many adv a ntages H igh sensitivity [ 10 -10 g ( flame ), 10 -14 g ( non-flame )] Good accuracy ( Relative error 0.1 ~ 0.5 % ) H igh selectivity

31. APPLICATIONS OF AAS W ater analysis (e.g. Ca, Mg, Fe, Si, Al, Ba content) Food analysis A nalysis of animal feedstuffs (e.g. Mn , Fe, Cu, Cr, Se,Zn ) Analysis of soils Clinical analysis ( blood samples : whole blood , plasma ,serum; Ca , Mg, Li , Na , K, Fe )