2. Introduction
• Introduced by Alan Walsh(1950)
• It is a method of elemental analysis
• Useful for determining trace metals in liquid
or biological samples
• Highly sensitive-can detect metal in conc.
Lower than 1ppm
3. Principle
• When a solution containing metallic species is introduced
into a flame, the vapour of metallic species will be
obtained.
• Some of the metal atoms may be raised to higher energy
level and emit characteristic radiation. But large amount of
metal atoms will remain in non emitting ground state.
• These ground state atom of particular element are
receptive of light radiation of their own specific resonance
wavelength.
• Thus, when a light of this wavelength passed through a
flame having atom of metallic species, part of light will be
absorbed and the absorption will be proportional to the
density of atom in the flame.
4. Instrumentation
Components:
• Radiation source: are of two types
• Hollow cathode lamp- emits spectral line of that metal which is
used in the cathod
• Electrodeless discharge lamp
• Chopper:
• It is a rotating wheel interposed between the hollow cathode
lamp and flame.
• Gives pulsating current in the photocell
• Atomiser:
• Flame atomiser: total consumption burner and premixed burner
• Non flame atomiser
5. • Nebulization of liquid sample:
• method of formation of small droplet from the liquid
sample
• Nebulization is done by use of a gas moving at high
velocity
• Monochromator:
• Function of monochromator is to select given absorbing
line from spectral line emitted from hollow cathode
• Common monochromator are prism and gratings
6. • Detctor:
• Photomultiplier tube is most suitable
• Has good stability if used with stable power supply
• Amplifier:
• It amplifies electric current
• Lock in amplifier are preferred to achieve excellent
signal to noise ratio(measure of signal strength relative
to background noise)
• Read out device:
• Digital read out device are used
7. Operation
• A meter is adjusted to zero absorbance when
blank solution is sprayed on the flame, and
rest of the light passes on to the
photomultiplier tube.
• Then the light solution containing absorbing
species is introduced a part of light is
absorbed, resulting in a decrease in light
intensity falling on a photomultiplier tube.
8. Types
• Single beam AAS:
• Light source is placed ahead of flame with mechanical
chopper between light source and flame
• Has low stability
• Double beam AAS:
• Beam from hollow cathod lamp is divided into two part
one passes through flame while other bypass it
9. Difference
AAS
• Amount of light absorbed by
ground state atom is
measured
• Absorption intensity doesnot
depend upon temperature
• Beers law is obeyed over wide
range of concentration
FES
• Amount of light emitted by
the excited atom is measured
• Is greatly influenced by
temperature variation
• Not obeyed
12. Advantages of AAS
• Technique is specific because the atom of
particular element can only absorb radiation
of their own characteristic wavelength
• Is independent of flame temperature
13. Disadvantages
• Separate lamp for each element to be
determined is required
• Technique cannot be used sucessfully for
estimation of element like Mo,Si etc because
these element give rise to oxide in the flame
• Predominant anion affect the signal to
negotiable degree
14. Application
• Qualitative and quantitative analysis
• Determination of metallic elements in
biological system
• Determination of metallic element in food
industry
• Determination of Ca, Mg, Na, K in serum
• Determination of lead in petrol
