1. ATOMIC ABSORPTION SPECTROSCOPY(AAS)
1 | P a g e
SubmittedTo Mam Khadijah
Submitted By AnumShahid – CMS#8168
AniqaJaved- CMS#13464
FaizaIftikhar– CMS#8420
SalehaSayyab – CMS#8571
KalsoomSaleem –CMS#8107
SubmissionDate 06-11-2014
Semester 6th
SectionA
Total Pages 9
Remarks
ASSIGNMENT
ATOMIC ABSORPTION
SPECTROSCOPY
v, 2014

2. ATOMIC ABSORPTION SPECTROSCOPY(AAS)
2 | P a g e
Table of Contents
Sr # Content Page #
1 Introduction 3
2 Basic Principle of AAS 4
3 Atomic Spectra 4
4 Instrumentation of AAS 5
5 Interpretation of AAS 7
6 Applications of AAS 8
7 References 9

3. ATOMIC ABSORPTION SPECTROSCOPY(AAS)
3 | P a g e
1. Introduction
Atomic-absorptionspectroscopyquantifiestheabsorptionof groundstate atomsinthegaseousstate.
The atoms absorb ultraviolet or visible light and make transitionsto higher electronic energy levels.
The analyte concentration is determined from the amount of absorption. Concentration
measurementsare usually determined from a working curve after calibrating the instrument with
standards of known concentration. Atomic absorption is a very common technique for detecting
metals and metalloids in environmental samples.
Whena solutioncontainingmetallicspeciesare introducedintoaflame,the vaporof metallicspecies
will be obtained. Some of the metal atoms may be
raisedtohigherenergylevel andemitcharacteristic
radiation. However, large amount of metal atoms
will remain in non-emitting ground state. These
ground state atoms of particular element are
receptive of light radiation of their own specific
resonance wavelength. Thus, when a light of this
wavelengthpassedthroughaflame havingatom of
metallic species, part of light will be absorbed and
the absorptionwillbe proportional tothe densityof
atom in the flame.
Elements determined from this technique as shown in Table 1.
Elements that can be detected by AAS
Aluminium (Al) Copper (Cu) Mercury (Hg) Cadmium (Cd) Calcium (Ca)
Antimony (Sb) Gallium (Ga) Molybdenum (Mo) Cobalt (Co) Chromium (Cr)
Arsenic (As) Hafnium (Hf) Niobium (Nb) Nickel (Ni) Lead (Pb)
Beryllium (Be) Indium (In) Ruthenium (Ru) Manganese (Mn) Lithium (Li)
Barium (Ba) Iron (Fe) Tin (Sn) Magnesium (Mg) Vanadium (V)
Tungsten (W) Vanadium (V) Zinc (Zn) Zirconium (Zr)

4. ATOMIC ABSORPTION SPECTROSCOPY(AAS)
4 | P a g e
The atoms in the atomizer get promoted to higher orbitals (excited state) for a short period of time
(nanoseconds) byabsorbingadefinedquantityof energy(radiationof agiven wavelength).Thisamount
of energy,i.e.,wavelength,isspecifictoaparticularelectrontransitionina particularelement.Ingeneral,
eachwavelengthcorrespondstoonlyone element,andthe widthof anabsorptionlineisonlyof the order
of a few Picometers (pm),whichgivesthe technique itselemental selectivity.The radiationfluxwithout
a sample andwitha sample inthe atomizerismeasuredusingadetector,andthe ratio betweenthe two
values (the absorbance) is converted to analyte concentration or mass using the Beer-Lambert Law.
2. Principle
The Beer–Lambert law:
Atomicabsorptionspectroscopyreliesonthe Beer-Lambertlaw todetermine the concentrationof a
particularanalyte inasample.The absorptionspectrumandmolarabsorbance of the desiredsample
elementare known,a knownamountof energyis passedthroughthe atomized sample andby then
measuring the quantity of light, it is possible to determine the concentration of the element being
measured. There is a linear relationship between absorbance and concentration of an absorbing
species.
A= Absorbance
l= path lenth of cell (cm)
c=molar concentration
= wavelength-dependent molar absorptivity coefficient
Applying Lambert-Beer’s law in atomic absorption spectroscopy is difficult due to variations in the
atomizationfromthe sample matrix andnon-uniformityof concentrationandpathlengthof analyte
atoms.Concentrationmeasurementsare usuallydeterminedfromacalibrationcurvegeneratedwith
standards of known concentration.
3. Atomic spectra
Atomic spectra feature sharp bands. For example hydrogen spectrum:
n = 1
n = 2
n = 3
energy
DE

5. ATOMIC ABSORPTION SPECTROSCOPY(AAS)
5 | P a g e
4. Instrumentation of AAS
Atomic absorption instruments consist of a
a. Radiation Source
b. Monochromator
c. Flame or electrothermal atomizer in which sample is introduced
d. Atomizer
e. Detector
a. Radiation Source
Althoughradiationinthe UV-Visregionisrequired,we cannotusebroadbandsources.Thisisbecause
even the best monochromators cannot provide a bandwidth that is narrower than the atomic
absorptionline.If the bandwidthof the incidentradiationiswiderthanthe line width,measurement
will fail asabsorptionwillbe onlyatinyfractionof a large signal whichisdifficulttomeasure andwill
resultinvery lowsensitivities(figure a).Therefore,line sourceswithbandwidthsnarrowerthanthat
of the absorption linesmust be used (figure b). This can be achieved by using a lamp producingthe
emission line of the element of interest where analyte atoms can absorb that line. Conditions are
establishedtoget a narrower emissionline thanthe absorption line.Thiscan in fact be achievedby
getting an emission line of interest at the following conditions:
1. Low temperatures: to decrease Doppler broadening
(whichiseasily achievablesince thetemperatureof the
source is always much less than the temperature in
flames).
2. Lower pressures: this will decrease pressure
broadening and will thus produce a very narrow
emission line. Atomic Line Width Monochromator
Bandwidth(differentScales)thismaysuggesttheneed
for a separate lamp for each element, which is
troublesome and inconvenient. However, recent
developments lead to introduction of multi-element
lamps. In this case, the lines from all elements should
not interfere and must be easily resolved by the
monochromator so that, at a specific time, a single line of one element is leaving the exit slit.
Hollow Cathode Lamp (HCL)
This isthe most commonsource in atomic absorption
spectroscopy.Itis formedfroma tungstenanode and
a cylindrical cathode the interior surface of which is
coated by the metal of interest. The two electrodes
are usuallysealedinaglasstube withaquartzwindow
and filled with argon at low pressure (1-5 torr).
Ionization of the argon is forced by application of

6. ATOMIC ABSORPTION SPECTROSCOPY(AAS)
6 | P a g e
about 300 V DC where positivelychargedAr+heads rapidlytowardsthe negativelychargedcathode
causingsputtering. A portionof sputteredatomsisexcitedandthusemits photonsasatoms relax to
groundstate.The cylindrical shape of the cathode servestoconcentrate the beaminalimitedregion
and enhances redisposition of sputtered atoms at the
hollow surface. High potentials usually result in high
currents,which,inturn,produce more intenseradiation.
However, Doppler broadening increases as a result. In
addition, the higher currents will produce high
proportion of unexcited atoms that will absorb some of
the emission beam, which are referred to as self-
absorption (a lower intensity at the center of the line is
observed in this case).
b. Monochromators
Thisis a veryimportantpart inan AA spectrometer. Itisusedto separate outall of the thousandsof
lines. Withoutagoodmonochromator,detectionlimitsare severelycompromised.A monochromator
is used to select the specific wavelength of light, which is absorbed by the sample, and to exclude
otherwavelengths.The selectionof thespecificlightallowsthedeterminationofthe selectedelement
in the presence of others.
c. Atomizer
Atomization is separation of particles into individual molecules and breaking molecules into
atoms.Thisisdone byexposingthe analyte tohightemperaturesinaflame or graphite furnace. The
role of the atomcell istoprimarilydissolvate aliquidsampleandthenthe solidparticlesare vaporized
into their free gaseous ground state form. In this form, atoms will be available to absorb radiation
emittedfromthe lightsource and thusgenerate a measurable signal proportional toconcentration.
There are two types of atomization: Flame and Graphite furnace atomization.
d. Flame Or Electrothermal Atomizer In Which Sample Is Introduced
There can be significant amounts of emission produced in flames due to presence of flame
constituents (molecular combustible products) and
sometimes impurities in the burner head. This emitted
radiation must be removed for successful sensitive
determinations by AAS, otherwise a negative error will
alwaysbe observed.The detectorwill seethe overall signal,
which is the power of the transmittedbeam (P) in addition
to the power of the emitted radiation from flame (Pe).
Therefore if we are measuringabsorbance,thiswill resultin
a negative errorasthe detectorwillmeasure whatitappears
as a high transmittance signal (actually it is P + Pe). In case
of emission measurements, there will always be a positive

7. ATOMIC ABSORPTION SPECTROSCOPY(AAS)
7 | P a g e
error since emission from flame is an additive value to the actual sample emission. It is therefore
obvious that we should get rid of this interference from emission in flames.
e. Detector
The lightselectedbythemonochromatorisdirectedontoadetectorthatistypicallyaphotomultiplier
tube, whose function is to convert the light signal into an electrical signal proportional to the light
intensity. A signalamplifierfulfillsthe processingof electrical signal. The signalcouldbe displayedfor
readout, or further fed into a data station for printout by the requested format.
5. Interpretation of AAS
Atomic theory tells us that the electrons in all atoms are in well-defined orbitals.For example,in
uranium, the electron shells with principal quantum number 1-6 are all filled and the shell with
principal quantumnumber7is partiallyfilled.Numerous orbital are available ineachshell thatare s,
p, d orbitals, etc. in the filledshell,each orbital accommodatesan electron. In the unexcited atoms,
these electronsreside inthe orbital withthe lowestenergylevel.However,the upperemptyorbital
is available to accommodate an electron. During excitationthe electrons with the lowest electron
moves from normal low-energy level to an orbital with a higher energy. This orbital may be in the
same shell or in a higher shell, inasmuch as each orbital is available to accommodate an electron
unless excluded by quantum theory-forbidden transitions.
Example:
In atomic sodium, electron fill the shells withquantum numbers 1 and 2, and one electron is in the
shell withthe quantumnumber3.Whenthe sodiumisin the ground state,thiswill be inorbital with
the lowest energy, i.e.,3s. if we excite sodium, the 3s electron can move to n orbital with higher
energy.The energylevel nexttothe 3slevel isthe 3penergylevel,hence itispossibleforanelectron
to go from a 3s to 3p orbital. It is also possible for the 3s electron to go into orbitals of evenhigher

8. ATOMIC ABSORPTION SPECTROSCOPY(AAS)
8 | P a g e
energy,suchas4p,4d,5p, 5d,etc. Whenthe valence electronsof sodiumisinthe 3sorbital,itslowest
energy state, the sodium is said to be in the ground state. When the electron is in any orbital with
higher energy, the sodium is said to be in excited energy state, or excited sodium. When radiation
energyisabsorbed,the atom becomesexcited.If we use a prism to disperse the radiationfallingon
the atoms,the absorptionspectrumappearsasaseriesof narrow linesopposedtowidebands.If the
transition is between the ground state and lowest
excited state, then it is said that the absorption line is
the resonance line. Transitions between the ground
state and the upper excitedstatesare possible butare
not oftenused.The energylevelsof sodiumare shown
in figure, forsake of clarity,upperstate transitionsare
omitted. In sodium, the transition between the 3s
orbital and a 3p orbital can be achieved by absorbing
radiations at 589 or 589.5 nm. Similar absorption of
radiation at 33.03 nm will cause sodium to be excited
fromthe 3s groundstate tothe 5p excitedstate orbital.
Transitions between the 3s orbital and orbitals with
principal quantum number 6 requires more energy.
6. Applications
1. It is used for water analysis for the presence of following content (e.g. Ca, Mg, Fe, Si, Al, Ba )
2. Also used in food analysis and soil analysis
3. In clinical analysis it is used for analyzing metals in biological fluids and tissues such as whole
blood, plasma, urine, saliva, brain tissue, liver, muscle tissue, semen
4. In Pharmaceuticalsithas applicationsinsome pharmaceutical manufacturing processes,minute
quantities of a catalyst that remain in the final drug product
5. It is used in petroleum industry, metallic impurities in petrol, lubricating oils have been
determined.
6. It is used in alloys, metallurgy and in inorganic analysis.
7. Used in analysis of many ores and minerals.
8. It is used in biochemical analysis such as used in estimation of sodium, potassium, zinc, lead,
cadmium, mercury, calcium, iron and magnesium.
9. Alsousedinpharmaceutical analysis,forestimationof zincininsulinpreparations,creamsandin
calamine,oils,calciumincalciumsalts,leadincalciumcarbonate andalsoas impurityinnumber
of chemical salts have been done.
10. Sodium, calcium, and potassium in saline and ringer solutions are estimated by this method.
11. Analysisof ashfordeterminingthe contentsof sodium, potassium, calcium, magnesiumandiron
is carried out in boiler deposits.
12. Used in cement industry.
13. Used in agriculture, soil, forestry, fertilizer and oceanography etc.
14. Used in assay of intraperitoneal dialysis, activated charcoal, cisplatin.

9. ATOMIC ABSORPTION SPECTROSCOPY(AAS)
9 | P a g e
7. References
a. James W. Robinson, Atomic Spectroscopy, Second Edition, page 100-102
b. M.Arora, Aseem Anand, Instrumental Method Of Chemical Analysis, Himalaya Publishin
House, Fifth Edition, 2005, Page 240-242
c. Aurora BiomedInc., AuroraInstruments.2014. http://www.aurorabiomed.com/atomic-
absorption-spectroscopy/
d. Hitachi High-TechnologiesCorporation. 2011-2014.
http://www.hitachi-hitec.com/global/science/aas/aas_basic_3.html
e. Galbraith Laboratories, Inc. 2011-2014. http://www.galbraith.com/spectroscopy.htm
f. M.Arora, Aseem Anand, Instrumental Method Of Chemical Analysis, Himalaya Publishin
House, Fifth Edition, 2005, Page 240-241