Atomic absorption spectroscopy is a method used to determine trace metals in liquids. It works by vaporizing the metallic species in a flame and absorbing light of a specific wavelength corresponding to the element. The amount of light absorbed is proportional to the number of atoms and can be used to determine the concentration. It has advantages over other methods in that the determination is independent of the chemical form of the metal in the sample. Some limitations include spectral and chemical interferences that can occur. It is commonly used for quantitative analysis to determine the amounts of various elements in applications like food analysis, biological samples, and environmental testing.

1. Mr.P.R.Jadhav,
Asst.Prof.
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2.  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. For example we can determine total cadmium
content of water sample-it does not matter whether the
cadmium exists as a chloride, sulfate, or other salt
form
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3.  AAS is an absorption method where
radiation is absorbed by non exited atoms
in vapour form.
 Atomization process.
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4.  When a solution containing metallic species
is introduced into a flame, the vapour of
metallic species will be obtained.
 These ground state atoms of a particular
element are receive of light radiation of
their own wavelength
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5.  Part of that light will be absorbed by
the particular element and the
absorption will be proportional to the
density of atoms in the flame. Thus, in
AAS, one determines the amount of
light absorbed. once this value of
absorption is known, the concentration
of the metallic element can be known.
 Mathematically the total amt of the
light absorbed may be given by
following equation 5

6.  Total amt of light absorbed =(ле2 /mc)Nf
 Where, e = charge on the electron of mass
 C= speed of light
 N = Total number of atoms
 f= oscillator strength
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8.  Light produced by special kind of lamp which
is able to emit the spectral lines which is
absorbed by the specific atoms .the sample
solution is aspirated into the flame.
 This vapour will be dissociated into atoms of
the element to be measured. Thus ,the flame
possesses free unexcited atoms which are
capable of absorbing radiation, from an
external source when the radiation
corresponds exactly to the energy required for
a transition element from ground state to
exited level
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9.  RADIATION SOURCE
 CHOPPER
 ATOMISERS
 NEBULIZATION OF LIQUID SAMPLE
 MONOCHROMATORS
 DETECTORS
 AMPLIFIER
 READ OUT DEVICE
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10.  HOLLOW CATHOD LAMP
 ELECTRODELESS DISHCHARGE LAMP
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12.  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.
 The lamp window is constructed of quartz,
silica, or glass.
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13.  When a potential is applied between the two
electrodes, the inert gas is charged at the
anode, and the charged gas is to the
cathode. The impact with the cathode
vapourizes some of the sodium atoms and
give rise to the sodium emission spectrum
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14.  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.
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15.  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.
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16.  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.
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17.  A rotating wheel is interposed between the
HCL and the flame. This rotating wheel is
known as chopper
 it is interposed to break the steady light from
the lamp into a pulsating light. This 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.
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18.  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.
 FLAME ATOMISERS
 NON FLAME ATOMISERS
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19.  A most common way is to use a flame which
is used for converting liquid into gaseous
state and also converting the molecular form
into atomic vapour.
 There two types of burners
 Total consumption burner
 Premixed burner.
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21.  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. Sample in liquid form then the flame
breaks into the droplets which are evaporated
and burns. Leaving the residue which is reduced
to atoms.
 Total consumption burners do use oxygen with
hydrogen or acetylene, gives very hot flames.
 Disadvantage is there it is noisy and hard to
use.
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22.  IN this burner, the sample is aspirated into a
large chamber by means of fuel gas and
oxidant under pressure.
 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.
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23.  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
s gas moving at high velocity, called
pneumatic nebulization.
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24.  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.
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26.  As soon as photon strikes the photocathode
an electrons is dislodged and photon is
accelerated to dynode I., resulting in the
liberation of two or more electrons from this
dynode. Similarly, the electrons from this
dynode I are accelerated to dynode 2,
resulting in the liberation of move electrons.
Thus, the current multiplied at each dynode
and the resultant electron current is received
by the anode which goes to external
amplifier and read-out system.
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28.  In the most of AAS measurement, chart
recorders are used as read out device. A
chart recorder is a potentiometer.
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29.  Absorption of Source Radiation: Element other
than the one of interest may absorb the
wavelength being used.
 Ionization Interference: the formation of ions
rather than atoms causes lower absorption of
radiation .This problem is overcome by adding
ionization suppressors.
 Back ground Absorption of Source Radiation :
This is caused by the presence of a particle from
incomplete atomization .This problem is
overcome by increasing the flame temperature.
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30.  Transport Interference: Rate of aspiration,
nebulization, or transport of the sample (e g
viscosity, surface tension, vapor pressure,
and density).
 Cation cation interference: invariably
decrease the signal intensity of the element
present in the sample. These are neither
spectral nor ionic in nature and mechanisms
of their interactions are unknown.
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31.  Anion cation Interference: the presence of
certain anions in solution may effect the
intensity of radiation emitted by an element and
thus results in a serious analytical error.
 Oxide formation Interference: this type of
Interference arises due to the formation of stable
oxides with free metal atoms if oxygen is
present in the flame. Thus, the emission
intensity is lowered because a large percentage
of free metal atoms have been removed from the
flame. All of the alkaline earth element from
oxides and are subject to this type of
Interference.
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32.  Spectral interference is caused by radiation overlap of absorption
line due to emissions from another element or compound.
Example 1: Vanadium line is 3082.11 A and Aluminium is at
3082.15 A. Choose a different Aluminium line at 3092.7 A.
Note: Interference due to overlapping lines is rare in AAS.
Spectral interference is also effected by the radiation of an emission
line of another element or compound, or background radiation from
flame, solvent or sample.
Example2: Radiation interference in the determination of Na with Mg
present, and in the determination of Iron with Cu or Ni present.
Use alternate wavelength.
Use smaller slit width.
Use blank.
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33.  CHEMICAL INTERFERENCES.
Chemical interference occurs when an analyte is not totally decomposed in flame. There is
less atoms present, and therefore a reduced absorbance of the analyte.
Compound Formation.
Compounds cannot be broken down in flame. Anions SO4 and PO4 combines with metal
to form stable compounds and decrease the absorption of the analyte.
Example 1:Calcium signal is depressed due to formation of CaSO4 or CaPO4.
Example2: Magnesium signal is depressed in the presence of Aluminium. Aluminium
forms heat stable compound with Mg.
Use Hotter flame
Use Releasing agent :
These agents reacts with the interferent. It is a cation that reacts with the interfering anion
and frees up the element to be analysed.
La an Sr are good releasing agents for Ca in the presence of SO4 and PO4.
La an Sr are also good releasing agents for Mg in the presence of Al.
Use Protective agent :
These agents form stable but volatile compounds. EDTA and 8-Hydroxy quinolone are
protective agents. They can complex Ca in the presence of SO4, PO4 or Al.
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34.  QUALITATIVE ANALYSIS : in atomic
absorption spectroscopy, a different HCL is
to be used for each element to be tested. It
means that an element which Is used in in
the construction of cathode of HCL, can be
detected only. As QUALITATIVE ANALYSIS
involves the checking of one element at a
time, it means that the process is very
laborious. There for , AAS is the seldom used
in practice for the purpose.
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35.  QUANTITATIVE ANALYSIS: it is used
determination of the amt of radiation
absorbed by the sample if the value of
radiation absorbed is substituted in equation.
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36.  Simultaneous malticomponent analysis is
available, such determination using
multicomponent HCL
 Determination of metallic elements in
biological materials:
 Determination of metallic elements in food
industry: copper, zinc, and nickel are the
most common toxic elements of interests to
food analysis
 Determination of calcium, magnesium,
sodium and potassium in blood serum
 Determination of lead in petrol.
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