Atomic absorption spectrometry analyzes samples by breaking them down into atoms and measuring the absorption of light of a specific wavelength by those atoms. It works by vaporizing a sample in a flame and passing light from a hollow cathode lamp of the element being analyzed through the flame. The extent to which light is absorbed is proportional to the number of ground state atoms present and can be used to determine the elemental composition of a sample. Key components of an AAS instrument include the hollow cathode lamp light source, the flame atomizer and fuel system to vaporize samples, a monochromator to select the wavelength of light, and a photomultiplier detector to measure light absorption.

1. IN 504 Analytical Instruments
Module 3
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Presented by;
Anju Sunny
CUSAT
Reference Text: R S Khandpur
“Handbook of Analytical Instrumentation”

2. ATOMIC ABSORPTION
SPECTROMETRY (AAS)
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3. Introduction
 UV/Vis, IR or Raman Spectrometry gives molecular functional
group information, but no elemental information.
 Atomic Absorption Spectrometry provides information on
elemental composition of sample or compound.
 It is based on the breakdown of a sample into atoms, followed
by the measurement of the atom’s absorption of light.

4. Principle of AAS
 A much larger number of the gaseous metal atoms will normally
remain in the ground state.
 These ground state atoms are capable of absorbing radiant energy
of their own specific resonance wavelength.
 If light of the resonance wavelength is passed through a flame
containing the atoms of the sample, then part of the light will be
absorbed
 The extend of absorption will be proportional to the number of
ground state atoms present in the flame.

5. Schematic diagram of an AAS

6. Schematic diagram of an AAS
Detector
Grating Monochromator

7. Instrumentation - Source of light in AAS
1) Hollow cathode lamp 2) Elecrodeless discharge lamp 3) Laser
 Hollow cathode lamp (HCL)
Anode : tungsten
Cathode : in the form of a cylinder, made of the element being
studied in the flame.

8. Instrumentation - Source of light in AAS
 The source of light is a
lamp whose cathode is
composed of the element
being measured.
 Each analyzed element
requires a different lamp.
• The cathode lamps are stored in
a compartment inside the AAS.
• The specific lamp needed for a
given metal analysis is rotated
into position for a specific
experiment.

9. Instrumentation – Fuel & Atomizer
 The sample is prepared in aqueous solution.
 A flame is created, usually using ethyne & oxygen (fuel) & the
solution is subjected into the flame by nebulizer.
 The flame gases flowing into the burner create a suction that
pulls the liquid into the small tube from the sample container.
This liquid is transferred to the flame where the sample is
atomized [mixing the sample with air to create fine droplets].
The metal atoms then absorb light from the source (cathode
lamp). 9

10. Sample is
vaporized
in the flame.
Aspirator
tube sucks the
sample into the
flame in the
sample
compartment.
Light beam
Instrumentation – Fuel & Atomizer

11. Instrumentation –
Monochromator, Detector, Read out
• The light passes through a Grating monochromater (a device
used to select a particular wavelength of light for observation)
• The intensity of the light is fairly low, so a photomultiplier tube
(PMT) is used to boost the signal intensity and the purpose of
detection.
• The read out specified by the user is displayed on the computer
screen for each sample measured.
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12. Advantages
 High sensitivity
 Good accuracy
 High selectivity
 Widely used
Disadvantage
 A resonance line source is required for each element to be
determined
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