This document describes atomic absorption spectroscopy (AAS), a technique introduced in 1950 for quantitative elemental analysis. AAS uses atomic absorption of light to determine the concentration of gas-phase metal atoms. Samples are atomized in a flame or graphite furnace then irradiated to promote electron excitation. Absorption of characteristic wavelengths is measured using a detector. AAS can detect metals down to ppm levels and is used to analyze biological, environmental, food, and other samples for various elements.

2.  This method was introduced by Alan Walsh in 1950
 Spectro-analytical procedure for the quantitative
determination of chemical elements employing the
absorption of optical radiations by free atoms in gaseous
state.
 AAS uses the absorption of light to measure the
concentration of gas-phase atoms.
 The absorption of light of free atoms is measured.
 Trace elements are determined with the help of this
method.
 Highly sensitive as it can detect metal in concentration
lower than 1ppm.
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3.  The technique makes use of absorption spectrometry
to assess the concentration of an analyte in a sample.
 It requires standards with known analyte content to
establish the relationship between the measured
absorbance and the analyte concentration.
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4.  the electrons of the atoms are in the atomizer are
promoted to higher excited state for a short period of
time by absorbing a defined quantity of energy i.e.
wavelength.
 This wavelength is specific to a particular electron
transition in a particular element.
 The radiation flux without a sample and with a sample
in the atomizer is measured using a detector and the
ratio between the two values is converted to analyte
concentration using Beer Lambert’s law.
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5.  The absorption follows Beer’s law-
 Absorption is directly proportional to the
concentration of atoms in the flame and to the path
length in the flame.
 Each element absorbs radiation that is characteristic of
that element.
 Therefore a separate lamp source is needed for each
element.
 Most commonly used source for light is hollow
cathode lamp(HCL).
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It is a sharp line source that emits specific monochromatic
wavelenghts.
It consists of-
- A cylindrical hollow cathode made of the element to be
determined or an alloy of it.
-Tungsten anode
These are enclosed in a glass tube usually with a quartz window.
The tube is under reduced pressure and filled with an inert
gas(neon or argon)

8.  A high voltage is impressed across the electrode
causing the gas atoms to be ionized at anode. These
positive ions are accelerated towards the cathode.
 When they bombard the cathode they become
vaporized.
 The vaporized metal is excited to higher electronic
levels with the continued collision with the high
energy gas ions.
 When the electrons return to ground state the
characteristic lines of that metallic element are
emitted.
 These HCL emitted lines are passed through the flame
and can become absorbed by the test element.
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9.  A suitable line from the radiation is selected for the
analysis.
 It is usually the most intense line in the emission spectrum
and represents a transition from an excited to the ground
state.
 It is also the correct frequency absorption by atoms in the
ground state in the flame. Such a line is called resonance
line.
 The flame is also emitting source and the photo tube
responds to the radiation from flame as well as from hollow
cathode lamp and will create an interference in absorption
measurements.
 This problem is corrected by a beam chopper.
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10.  It contains a small quantity of analyte as a metal or a
salt in a Quartz bulb together with an inert gas (argon)
at low pressure.
 The bulb is inserted into a coil that is generating an
electromagnetic radio frequency field resulting in a
low pressure inductively coupled discharge in the
lamp.
 The emissions from EDL are higher than from HCL
and the line width is generally narrower but ELDs
need a separate power supply.
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11.  It is a rotating wheel interposed between the hollow
cathode lamp and the flame.
 It gives pulsating current to the photocell.
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12.  There are two types of atomizers-
Flames(spectroscopic)
electrothermal (graphite tubes)
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13.  Flame atomizer-
 oldest
Most commonly used
 They are of two types- air acetylene flames with a
temperature of about 2300 and nitrous oxide acetylene
flame with temperatures about 2700.
 Liquid or dissolved samples are used with flame
atomizers
 In this case sample solution is aspirated by a
pneumatic analytical nebulizer, transformed into a
spray chamber where it is mixed with flame and
conditioned in s way that only the finest aerosol
droplets enter the flame.
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14.  The process in the flame includes-drying
vaporization
atomization
ionization
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15.  Electro-thermal atomizer-
 Graphite tube atomizer
With this technique liquid, solid and gaseous samples
may be analyzed directly.
 Stages-drying
pyrolysis
atomization
cleaning
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Flame AAS
 A steady state signal is
generated during the
time period.
 Less sensitive
 More interferences
Electrothermal AAS
 A transient signal is
generated.
 Sensitivity is 2 to 3 times
higher than flame AAS.
 Less interferences.

17.  The function of monochromator is to select given
absorbing line from spectral line emitted from hollow
cathode.
 Common monochromators are- prisms
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18.  Photomultiplier tubes are most commonly used as
detectors.
 They have good stability when used with stable power
supply.
 Digital read out devices are used.
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19.  Technique is specific because the atom of particular
element can only absorb radiation of their own
characteristic wavelength.
 It is independent of flame temperature.
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20.  Separate lamp for each element to be determined is
required.
 Technique cannot be used for estimation of element
like Mo, Si because these give rise to oxide in the
flame.
 Predominant anion affect the signal to negotiable
effect.
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21.  It can be used for qualitative and quantitative analysis.
 Determination of metallic elements in biological
system.
 Determination of Ca,Mg,Na,K in serum.
 Determination of lead in petrol
 Food analysis
 Water analysis (Ca,Mg,Fe,Si,Al,Ba content)
 Analysis of soil
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