1. Satish Pradhan Dnyanasadhana College, Thane Department of Chemistry T
Satish Pradhan Dnyanasadhana College, Thane Department of Chemistry T.Y.B.Sc. Analytical Chemistry Paper-IV Sem-V Atomic Absorption Spectroscopy

2. Contents
3.1.4 Atomic Absorption Spectroscopy – Principle, Instrumentation
(Source, Chopper, Flame and Electrothermal Atomizer)
3.1.5 Quantitative applications of Flame Photometry and Atomic
Absorption Spectroscopy – Calibration curve method,
Standard addition method and Internal standard method.
3.1.6 Comparison of Flame Photometry and Atomic Absorption
Spectroscopy
3.1.7 Applications and Limitations of Flame Photometry and Atomic
Absorption Spectroscopy.

3. Atomic Absorption Spectroscopy
UNIT-IV

4. Introduction
In Analytical chemistry Atomic absorption spectroscopy is a technique for determining the concentration of a particular metal element in a sample. Atomic absorption spectroscopy can be used to analyze the concentration of over 62 different metals in a solution.

5. Atomic Absorption Spectra
Excited state E2
Hollow cathode
Lamp
Ground state E1

6. Technique
The technique typically makes use of a flame to atomize the sample, but other atomizers such as a graphite furnace are also used.
Three steps are involved in turning a liquid sample into an atomic gas:

7. Three steps In AAS
Three steps are involved in turning a liquid sample into an atomic gas:
Desolvation – the liquid solvent is evaporated and the dry sample remains
Vaporization – the solid sample vaporizes to a gas
Volatilization – the compounds making up the sample are broken into free atoms

8. Excited Gaseous Metal atoms
M+ X-
Sample Solution
M+ X-
Fine Mist
Solid Particles
M X
Gaseous
Molecules
M X
Gaseous Atoms
M(g)+ X(g)
Excited Gaseous Metal atoms
Large no. of Ground State gaseous atoms absorbs radiation of their own wavelength
Principle of F.E.S

9. Instrumentation
The Instrument used in AAS is called as ATOMIC ABSORPTION SPECTROPHOTOMETER
The Components are
Radiation Source :Hollow Cathode Lamp
Rotating Chopper
Atomisation Unit
Monochromator
Detector and Amplifier
Read out device

10. Atomic Absorption Spectrophotometer
Rotating Chopper
Hollow
Cathode
Lamp
P.M.T.Detector
Flame
Amplifier
Read Out
Grating
Power
Supply
Sample Solution

11. + + M M Radiation Source Hallow Cathode Lamp Glass Shield Inert Gas
Anode + +
Quartz Window +
_______________________________________ M
Cathode
---- M
Hallow Cathode Cup

15. Radiation Source : Radiation Source :Hollow Cathode Lamp
HCL is the most common radiation source in atomic absorption spectroscopy. The lamp consist of glass tube. The Lamp is filled with argon or neon gas. The cathode is a cylindrical metal cathode containing the metal for excitation, and an anode. When a high voltage is applied across the anode and cathode, gas particles are ionized. As voltage is increased, gaseous ions acquire enough energy to eject metal atoms from the cathode. Some of these atoms are in excited states and emit light with the frequency characteristic to the metal. Many modern hollow cathode lamps are selective for several metals.

16. Events in Hollow cathode Lamp: Reactions in the hollow-cathode lamp
ionization of filler gas: Ar + e- ® Ar+ + 2 sputtering
of cathode atoms: M(s) + Ar+ ® M(g) + Ar
excitation of metal atoms: M(g) + Ar+ ® M*(g) + Ar
light emission: M*(g) ® M(g) + hV.
The cathode contains the element that is analysed. Light emitted by hallow-cathode lamp has the same wavelength as the light absorbed by the analyte element. Different lamp required for each element (some are multielement)

17. The type of hollow cathode tube depends on the metal being analyzed
The type of hollow cathode tube depends on the metal being analyzed. For analyzing the concentration of copper in an ore, a copper cathode tube would be used, and likewise for any other metal being analyzed. The electrons of the atoms in the flame can be promoted to higher orbitals for an instant by absorbing a set quantity of energy (a quantum).

18. 2.Rotating Chopper:
Resonance radiation given by hollow cathode lamp as well as sample atoms in flame due to thermal excitation are detected by detector which creates an interference in absorbance measurement.
To eliminate the radiation coming from atom in flame by excitation of atoms. Rotating chopper is used.
Rotating chopper is arrange in between flame and Hollow cathode lamp.
It is circular disc divided into four quarters, out of which two are mirrored and two are opened.
When disc rotates at high speed when the mirror quartered in front of the lamp it reflects the radiation.
The second moment it opens in front of lamp and radiation passes to sample being absorbed by it and reaches the detector in pulses.

19. 2.Rotating Chopper:
Steady light from hollow cathode lamp is broken into an irregular beam or pulsating light.
This gives alternating/pulsating current in the PMT detector. This alternating/pulsating current is amplified by amplifier.
The radiation emitted by atoms in flame produces a steady current which is not amplified.

20. Atomization Unit Disadvantages of Flame atomizer:
1) Total consumption Burner
2) Laminar flow burner
Electro thermal Atomizer
Disadvantages of Flame atomizer:
A large portion of sample flows down the drain
The residence time atoms in optical path is very short less than seconds.

21. ELECTRO THERMAL ATOMIZER (Graphite furnace).
PMT DETECTOR

22.  ELECTRO THERMAL ATOMIZER (Graphite furnace).
Electro Thermal Atomizer also called as Graphite furnace. Consist of hollow graphite tube 5cm long and 1 cm internal diameter. The tube is opened at both ends and has central hole to introduce of sample by micropipette. This tube is arranged in such a way that radiation from the source passes along the axis of the tube. Two electrodes are fitted at the end of the tube. The inert gas like neon or argon is allowed to flow over the tubes to avoid the oxidation of graphite. The tube is surrounded By water cooled metal jacket. The solution of the sample to be analysed (1-100ul) is introduced by inserting the micro pipette through the port in the outer jacket and gas inlet in the centre of graphite tube. The graphite cylinder is then heated by the passage of electric current to a temperature that is enough to evaporate the solvent from the solutions. The current is then increased.

23. STAGES IN ELECTRO THERMAL ATOMIZER
Drying stage
Ashing stage
Atomization stage
Temperature Range
Temperature of the furnace is maintained above the boiling point of the solvent.
For aq. Solution furnace temperature is adjusted to 383K for 30 Sec
Temperature of the furnace is maintained at 600K -1500K for period of 45 sec.
Temperature of the furnace is maintained at 2300K -3300K for period of 5 sec.
Function
Solvent undergoes evaporation
Organic substance are volatilized and other chemical matrix of the sample is destroyed
Gaseous atoms of metal are formed

24. Advantages:
Temperature that is enough to ash the sample and to produce the metal atoms.
The sample volume is small
No need for fuel -oxidant mixture.
High sensitivity
No flame noise.
Solid sample can be used directly.
Heat distribution is uniform and temperature is steady.

25. 4) Monochromator:
Prism or grating monochromator are used in AAS. The function of the monochromator is to select a given absorbing line from spectral lines by emitting hallow cathode lamp.

26. Atomic Absorption Spectrophotometer
Rotating Chopper
Hollow
Cathode
Lamp
P.M.T.Detector
Flame
Amplifier
Read Out
Grating
Power
Supply
Sample Solution

28. Applications of Atomic Absorption Spectroscopy
Water analysis (e.g. Ca, Mg, Fe, Si, Al, Ba content)
Food analysis
Analysis of animal Feedstuffs (e.g. Mn, Fe, Cu, Cr, Se, Zn)
Analysis of additives in lubricating oils and greases (Ba, Ca, Na, Li, Zn, Mg)
Analysis of additives in lubricating oils and greases
(Ba , Ca, Na, Li, Zn, Mg)
Analysis of soils
Clinical analysis (blood samples: whole blood, plasma, serum; Ca, Mg, Li, Na, K, Fe)

29. Advantages over flame atomic absorption spectroscopy:
Solutions, slurries and solid samples can be analysed.
Much More Efficient Atomization
Greater sensitivity
Smaller quantities of sample (typically 5 – 50 uL)
provides a reducing environment for easily oxidized elements
Disadvantages
Expensive
Low precision
Low sample throughput
Requires high level of operator skill

30. Distinguish between FES and AAS
Solutions, can be analysed.
Much More Efficient Atomization
Lesser sensitivity
Larger quantities of sample.
Alkali metal and alkaline earth metals can be determined
AAS
Solutions, slurries and solid samples can be analysed.
Much More Efficient Atomization
Greater sensitivity
Smaller quantities of sample (typically 5 – 50 uL)
Alkali metal and transition metals can be determined(64 elements)

31. Distinguish between FES and AAS
Different hollow cathode lamps are required as source of radiation
Chopper is used to eliminate radiation emitted from flame.
The quality of monochromator should no be of very high degree .
AC. Amplifier is used to amplify only AC Current.
 The absorption intensity depends upon unexcited atoms. 
signal is obtained due difference of energies between excited and ground state atom.
High degree operator is not required
FES
Flame serves as source for different element.
Chopper is not used .
The quality of monochromator should be of very high degree
Amplifier is used to increase the output signal of detector.
The emission intensity depends upon excited atoms.
Signal is obtained from wavelength emitted by atoms.
High degree operator is required

32. Distinguish between FES and AAS
The technique is expensive (cost Lakh).
 Solutions, slurries and solid samples can be analysed.
Much More Efficient Atomization.
Greater sensitivity.
Smaller quantities of sample (typically 5 – 50 uL)
Alkali metal and transition metals can be determined(64 elements)
FES
The technique is not so expensive (cost thousands only)
Only Solutions, can be analysed.
Less Efficient Atomization
Lesser sensitivity
Larger quantities of sample.
Alkali metal and alkaline earth metals can be determined.

33. Applications of Atomic Absorption Spectroscopy
Water analysis (e.g. Ca, Mg, Fe, Si, Al, Ba content)
Food analysis
Analysis of animal Feedstuffs (e.g. Mn, Fe, Cu, Cr, Se, Zn)
Analysis of additives in lubricating oils and greases (Ba, Ca, Na, Li, Zn, Mg)
Analysis of additives in lubricating oils and greases
(Ba , Ca, Na, Li, Zn, Mg)
Analysis of soils
Clinical analysis (blood samples: whole blood, plasma, serum; Ca, Mg, Li, Na, K, Fe)

34. Quantitative Analysis
Calibration Curve method
Standard addition method
Internal Standard addition method

35. Calibration Curve method

36. Standard addition method
In this method the absorbance of unknown (X) is first found out by aspirating into flame against blank.Then a series of standards having definite amount of unknown (X) plus varying amount of standard are prepared and diluted to same volume in each case .Their absorbance are then obtained . A graph of absorbance (A) against concentrations of standard (S) gives a linear curve. The concentration of the unknown can be determined by extrapolation of line which cuts to X axis.

37. . . . . . Standard addition method Absorbance--- X X+S X+2S X+3S X+4S
Absorbance---
X X+S X+2S X+3S X+4S
Concentration-----
Concentration of Unknown.

38. Internal Standard addition methodAx
----- At
Concentration-----