Atomic absorption spectroscopy involves atomizing a liquid sample and measuring the absorption of light from a lamp that emits light of a specific wavelength corresponding to the element being measured. The technique was introduced in 1955 and involves using a flame or graphite furnace to atomize the sample, a monochromator to select the wavelength of light, and a detector to measure the absorption. Common interferences include overlap of spectral lines, incomplete dissociation of compounds, and physical effects related to viscosity, solvent, and ionization. Atomic absorption spectroscopy is widely used for trace metal analysis in applications such as clinical analysis, environmental monitoring, pharmaceuticals, and mining.

1. HISTORY
• The technique was introduced in 1955 by Alan Walsh in
Australia ( 1916 – 1998 ).
• The first commercial atomic absorption spectrometer
was introduced in 1959.
The application of atomic
absorption spectra to chemical
analysis

2. PRINCIPLE
 Atomic absorption spectroscopy is a method of elemental
analysis. It is particularly useful for determining trace
metals in liquids and is most independent of molecular
form of the metal in sample.
 It is the absorption phenomenon.
 When a sample solution is aspirated into the flame, the
solvent is vaporised leaving particles of the solid salt.
 The salt burns and converted into the gasses form which
is dissociated into free neutral atoms and some of them
excited by the flame heat. Remaining atoms in the ground
state absorbs light of specific wavelength emitted by the
lamp of same element to be determined and the intensity
of the light absorption is measured.

3. Atomic absorption spectroscopy is a quantitative method of
analysis that is applicable to many metals and a few
nonmetals.
It is very reliable and simple to use.
It can analyze over 62 elements.
Elements detectable by atomic absorption are highlighted in pink in this periodic table

4. BOLTZMANN DISTRUBUTION EQUATION
N*/No = e - ∆E/kT
N* – number of excited atoms
N
o – number of unexcited atoms
∆E – difference in energies of two levels
K – Boltzmann constant
T – temperature of the flame

5. INSTRUMENTATION
 Radiation source
 Chopper
 Atomiser
 Monochromators
 Detector
 Amplifier
 Read out device

7. Types of AAS

8. Radiation source
1. Hollow Cathode Lamp (HCL)

9. The cathode consists of a hollow cup. In the
cup is the element which is determined.
The anode is tungsten wire. The two
electrodes keep in a tube containing an inert
gas (Ne or Ar).
The lamp window is constructed of quartz,
silica, or glass.

10. When a potential (300-500 V) is applied between two
electrodes, The electric discharge ionizes the inert gas (Ne or Ar
usually) atoms filled in the hollow tube, which in turn, are
accelerated into the cathode with high velocity and sputter
metal atoms into the gas phase. Metal atoms become excited
and after returning to ground state give rise to metal emission
spectrum.

11. The neon or helium gas in the hollow cathode lamp
performs three functions
 It dislodges atoms from the surface of the cathode
 responsible for excitation of the ground state metal atoms
 It is main source of current carrying capacity in the HCL.
• The pressure maintained in the lamp is 1 to 5 torr.
• The spectral lines produced by the HCL are so narrow that
they are completely absorbed by the atoms.
• Each hollow cathode lamp emits the spectrum of the metal
which is used in the cathode, for example copper cathode
emits copper spectrum which is absorbed by copper atoms.

12. 2. Electrodeless Discharge Lamp (EDL)
 It is difficult to make stable hollow cathode lamp
from certain elements particularly those that are
volatile, such as arsenic, germanium.
 An alternative light has been developed in the EDL. It
consists of an evacuated tube in which the metal of
interest is placed. The tube is filled with argon at low
pressure and sealed off. The sealed tube is then placed
in microwave discharge cavity.
 Under these conditions the argon becomes a plasma
and cause excitation of the metal sealed inside the
tube. The emission from the metal is that of its
spectrum.

13. CHOPPER
 A rotating wheel is interposed between the hollow
cathode lamp and flame .This rotating wheel is known
as chopper.
 It is interposed to break the steady light coming from
the lamp into pulsating light which is used to measure
the intensity of light absorbed by elements without
interference by radiation from the flame itself.
 Pulsating light gives pulsating current in photocell.
There is also steady current caused by light which is
emitted by flame. But only pulsating current is
amplified and recorded.

15. ATOMISER
 Atomization is separation of particles into individual
molecules and breaking molecules into atoms .This is
done by exposing the analyte to high temperatures in a
flame or graphite furnace
 Atomiser converts the liquid into small droplets which
are easily vaporised.
 Types of atomisers :-
1. Flame atomiser:-
a.) Total consumption burner
b.) premixed burner
2. Non-flame atomiser

16. a). Total consumption burner
 In this whole sample is atomised into the flame, hence named as
total consumption burner.
 Disadvantages
Noisy and hard to use.
 In this burner, the sample solution,
the fuel, and oxidizing gases are
passed through separate passages to
meet at the opening of the base of
flame. Then the flame breaks the
sample in liquid form into the
droplets which are evaporated and
burns. Leaving the residue which is
reduced to atoms.
 Fuel used – H2 /acetylene
 Oxidant – O 2

17.  b). Premixed burner
 It is most widely used because of uniformity in flame intensity.
 In this the sample solution ,fuel and oxidant are mixed before
they reach the tip.
 The fine droplets get carried out along with the fuel gas at outlet,
the large drops of sample get collected in chamber and are drained
out.
Advantages
Non-turbulent
Noiseless
Stable
Disadvantages
Only 5% sample
reaches
to the flame and rest
95% is wasted.

18. Temperature of some flames
Fuel oxidant Temperature (K)
H2 Air 2000-2100
C2H2 Air 2100-2400
H2 O2 2600-2700
C2H2 N2O 2600-2800
For some elements that form refractory oxides (molecules hard
to break down in the flame) nitrous oxide (N2O) needs to be
used instead of air (78% N2 + 21% O2) for the oxidant. In that
case, a slightly different burner head with a shorter burner
slot length is used.

19. Non flame atomiser
 The graphite furnace is an electro thermal atomiser
system that can produce temperatures as high as 3,000°C.
The heated graphite furnace provides the thermal energy
to break chemical bonds within the sample held in a
graphite tube, and produce free ground state atoms.
 The ground-state atoms are capable of absorbing energy,
in the form of light, and are elevated to an excited state.
The amount of light energy absorbed increases as the
concentration of the selected element increases.

20. Non flame atomiser

21. GRAPHITE TUBE ATOMIZER:
• uses a graphite coated furnace to vaporize the sample.
• ln GFAAS sample, samples are deposited in a small
graphite coated tube which can then be heated to vaporize
and atomize the analyte.
• The graphite tubes are heated using a high current power
supply.

22. NEBULIZATION
Before the liquid sample enters the burner ,it
is converted into droplets this method a
formation of small droplets its called
nebulization
Common method of nebulization is by use of
gas moving at high velocity, called pneumatic
nebulization.

23. MONOCHROMATORS
 This is a very important part in an AA spectrometer.
It is used to separate out all of the thousands of lines.
 Without a good monochromator, detection limits are
severely compromised.
 A monochromator is used to select the specific
wavelength of light which is absorbed by the sample,
and to exclude other wavelengths. The selection of
the specific light allows the determination of the
selected element in the presence of others.
They are of two types:
1) Prism
2) Grating

24. Prism monochromator :-
Quartz material is used
for making prism, as
quartz is transparent over
entire region
Grating monochromator :-
it consists of a series of
parallel straight lines cut
into a plane surface

25. DETECTORS

26. READ OUT DEVICE
• In the most of AAS measurement, chart
recorders are used as read out device. A
chart recorder is a potentiometer.

27. INTERFERENCE
Interference is a phenomenon in which two waves
superimpose to form a resultant wave of greater or lower
amplitude. Interference decrease the intensity of absorption of
light . Interference usually refers to the interaction of waves
that are correlated or coherent with each other, either because
they come from the same source or because they have the same
or nearly the same frequency.
Types of interferences
1) Spectral interference
2) Chemical interference
3) Physical interference

28. Spectral interferences
 Spectral interferences arise when the absorption or emission
of an interfering species either overlaps or lies so close to the
analyte absorption or emission that resolution by the
monochromator becomes impossible. ex:-Manganese triplet
(4031,4033,4035Å) overlapped by gallium line(4033Å).
 This interference can be corrected by amplitude modulation
of the source.
Chemical interference
 Occurs due to incomplete dissociation of compounds in the
flame when the concentration of compound is more.
 Removed by use of higher flame temperature.
 Chemically –by addition of more thermally stable compound.
ex-addition of lanthanum to the aluminium and magnesium
for detection of magnesium

29. Physical interference :-viscosity
-solvent
-ionization
1) Viscosity – viscosity is invertionaly proportional to the
intensity of absorption.
2) Solvent – organic solvent increases the intensity and
aqueous solvent decreases the intensity of absorption.
3) Ionization – occurs due to high flame temperature. A
number of vaporized atoms become ionized by the flame.
Resulting ions absorb at a different wavelength than the
vaporized atoms the new wavelength will not be selected by
the monochromator and low results occurs.
Na  Na+ + e-
Overcome by addition of more easily ionizable element
Ex- ionization interference of Na is corrected by the addition
of Potassium to the Sodium .

30. APPLICATION
Clinical analysis: Analysing metals in biological fluids such as blood
and urine.
Environmental analysis: Monitoring our environment – eg finding
out the levels of various elements in rivers, seawater, drinking water,
air, petrol and drinks such as wine, beer and fruit drinks.
Pharmaceuticals: In some pharmaceutical manufacturing processes,
minute quantities of a catalyst used in the process (usually a metal)
are sometimes present in the final product. By using AAS the amount
of catalyst present can be determined.
Industry: Many raw materials are examined and AAS is widely used
to check that the major elements are present and that toxic
impurities are lower than specified – eg in concrete, where calcium
is a major constituent, the lead level should be low because it is
toxic.
Mining: By using AAS the amount of metals such as gold in rocks
can be determined to see whether it is worth mining the rocks to
extract the gold.

31. Calibration Curve
• A calibration curve is used to determine the unknown
concentration of an element in a solution. The instrument is
calibrated using several solutions of known concentrations.
The absorbance of each known solution is measured and then
a calibration curve of concentration vs absorbance is plotted.
• The sample solution is fed into the instrument, and the
absorbance of the element in this solution is measured .The
unknown concentration of the element is then calculated
from the calibration curve