Atomic Absorption Spectroscopy (AAS)

These slide introduce the concept of atomic absorption for elemental analysis and highlight the basic principles and instrumentation of AAS.

1. Atomic Spectroscopy
Dr. SajjadUllah
Institute of Chemical Sciences
University of Peshawar, Pak

2. Optical AtomicSpectroscopy
Optical Spectrometry
Absorption
Emission
Fluorescence
Source: R. Thomas, “Choosing the Right Trace
Element Technique,” Today’s Chemist at Work, Oct.
1999, 42.

4. AAS
Higher number
of neutral atom (ground state)
AES
Higher number
of neutral atom (Excited state)
AFS
Higher number
of neutral atom (Excited state).
Emission measured at 90°

5. Principle of AAS
Theelementbeingdeterminedmustbereducedtothe
elementalstate,vaporized,andimposedinthebeam
oftheradiationinthesource.
AbsorptionofEMR(UV-Vis)byneutralatomsin
gaseousstate
SameprincipleasmolecularElectronicspectroscopy
butsampleholding,equipmentandspectraare
different
Source
Sample
P P
0
Chopper
λ-Selector
Detector
Signal Processor
Readout
Flame acts both as cell and solution

6. A. Walsh, "The application of atomic
absorption spectra to chemical analysis",
SpectrochimicaActa, 1955,7, 108-117.
http://www.science.org.au/academy/memoirs/walsh2.htm#1
The invention of hollow cathode lamp by Walsh in 1955 made practical
applications of AAS possible

7. Types of transitions/Energy level diagram
Atomic spectra: single external electron (Na or Mg
+
)
Doublet: Slightly
different in E
(LS coupling)
3p to 5s line
is weak, why?
unique λ-pattern
But depends on E
of source
λfor Mg
2+
are
shorter than Na
1s
2
2s
2
2p
6
3s
1

8. Why a doublet for p-orbital?
When e
-
spin is parallel to orbital motion (L+S), E is High (repulsive interaction b/w the fields)
When e
-
spin is opposite to orbital motion (L-S), E is Low (attractive interaction b/w the field)
The magnitudes of such splitting for d and f orbitals are small
Both the spin and the orbital motions create magnetic fields
owing to rotation of charge carried by the electron
A doublet line is observed for species containing single e
-
: Na, Mg
1+
, Al
2+
Higher no of e
-
, complex spectra (e.g., Fe, U have hundreds of such
electron transitions as shown in the simple Na

9. Atomic spectrum Mg
Singletground state Tripletexcited stateSingletexcited state
Spins are paired
No split
Spins are unpaired
Energy splitting

10. 1s
2
2s
2
2p
6
3s
2
Paired spin
No splitting Three lines

11. Excitation in flame
(Temperature Effects)
Boltzmann equation
Boltzmann Equation relates Excited state population/Ground State
population ratios to Energy, Temperature and Degeneracy
N
j/N
ois exponentially related to T
Effects on AAS and AES)exp(
00 kT
E
g
g
N
N
jj 

k= 1.38 x10
-16
erg/degree
∆E btw ground and excited states
g = statistical weight factors
g= 2J+1 (J= L±S)
J is the internal atomic quantum number for the atom in
particular energetic level

12. For Na (3s3p @ 598nm) at 2600 K2600) x 10^-16 x /1.381210^ x (3.72-
o
e )
2
4
(
N
*N
-

N*/N
o= 1.67 x 10
-4
<0.02%atomsarein
excitedstate

13. Boltzmann Distribution
All systems are more stable at lower energy. Even in the flame, most of the atoms will be in their
lowest energy state.
At 3000K, for every 7 Cs atoms available for emission, there are 1000 Cs atoms available for
absorption.
At 3000 K, for each Zn available for emission, there are approximately 1000000000 Zn atoms
available for absorption.
N
j= 10
-12
to 1 in most cases

14. Intensity of Emission Line
I = A N
jhν
I = A hνN
o(g
j/g
0) e^-∆E/kT
A = Einstein transition probability
A= 1/life time of e in excited state
or = 1/ no. of transition per second
(A = 10
8
s
-1
)
N
j = no. of atoms in excited state
N
j= N
o(g
j/g
0) e^-∆E/kT
With increase in T, N
jincreases
and I
emissionincreases
The line that is used for AAS measurement is the one for which the
intensity (as predicted by above equation) is maximum
Most intense line generally has the highest g
jA values*
gjA valaues are listed in: Corliss C. H. and Bozman, Experimental transition probabilities for spectral lines of 70
elements, NBS monograph 53, NBS, Washington D.C., 1962,

15. AAS vs. AES (Effect of T)
Both occur in flame
AES: I
emissionis dependent on concentration of atoms in the excited
state (↑N
j/N
o)
-more dependent on T
AAS: I
absorptionis dependent on concentration of atoms in the ground
state( ↓N
j/N
o)
-less dependent on T (however no of reduced atom↑with↑T
-high T, more no. of reduced atoms, more P broadening
-FWHM ↑and peak height ↓ with↑ in T (fast moving atoms,
Doppler Broadening)
FLAME TEMPRATURE must be CONTROLLED!

16. Line Broadening
Natural Line width: 10
-5
nm
Observed Line width: 0.001-0.01 nm
Two main Reasons:
(i) Doppler Broadening
(ii) Pressure Broadening
The narrow band of absorbed or emitted radiation that is observed
is called a spectral line

17. Line Broadening
Doppler broadening
Doppler shift:
The wavelength of radiation emitted or absorbed by a
rapidly moving atom decreases if the motion is toward a
transducer, and increases if the motion is receding from
the transducer.
λ↑
λ↓

18. The measured speed of light is fixed but frequency and
wavelength of the radiation can change as a result of motion of
the source
The product λνalways equal the speed of light in a fixed medium
As the velocity of the emitting atom towards the detector increases,
the observed frequency (ν
0) also increases.
As the emitting atoms are in random motion (T may effect!), a series of
overlapping lines (broadening ) is observed
Source: Halliday, D., and R. Resnick: Physics for students of science and engineering, Wiley, NY, 1962, p-915

19. Line Broadening
Pressurebroadening(collisionalbroadening)
Causedbycollisionsoftheemittingorabsorbing
specieswithotherions,molecules(e.gflamegases)
oratoms.
OccurswhenPissufficienttocausecollision.
Collisonsshortenthelifetimeofexcitedstate.
Frequencyisafunctionofthetimespentinexcited
state,achangeinfrequencyoccurs(broadning)
HighpressureHgandxenonlamps,continuum
spectra!

20. Atomic Spectroscopy
Sample Introduction
Flame
Furnace
ICP
Sources for Atomic Absorption/Fluorescence
Hollow Cathode Lamps and other Line Sources
Sources for Atomic Emission
Flames
Plasmas
Wavelength Separators + Slits +Detectors

21. 21
Instrumentation (AAS)
Line
source
Monochromator Detector
Read-outNebulizer
Schematic diagram of a AA spectrophotomer
Atomization

22. Readout device
(line source)
Flame (cell + solvent)
AA Spectrophotometer

23. The Atomic Absorption
Spectrometer
Atomic absorption spectrometers have 4
principal components
1 -A light source ( usually a hollow cathode
lamp )
2 –An atom cell ( atomizer )
3 -A monochromator
4 -A detector , and read out device .

24. Atomic Absorption
Spectrophotometer

25. Sample is
vaporized
in the flame.
Aspirator
tube sucks the
sample into the
flame in the
sample
compartment.
Light beam

26. Line Sources
Hollow Cathode Lamp
Conventional HCL
EDL
Radiation Sources for AAS

27. A = log P
o/P = k C

28. So Source Intensity, I, must be very high within this
narrow absorptive bands.
Why?
EMR Sources fo AAS
Sufficient radiation to permit accurate measurement at the detector
can be achieved only if I of the EMR is high.
Important Considerations!!!
Atomic Spectral lines are very narrow (0.001-0.01 nm)
This requirement is not that critical for molecular electronic
spectroscopy as Molecule absorb in broader range and even broad
EMR band (= band pass of monochromator) can be absorbed.

29. Xenon short-arc lamp
Continuous source used for AAS
λ-range 200-700 nm
Requires a monochromator for λ
selection
Advantage?
Disadvantage?
Xegas
Electric arc between two electrode causes
excitation of Xe filled in a quartz tube
and Xe atoms/ions upon de-excitation
give continuous spectrum

30. Line Sources (AAS)
Hollow Cathode Lamp (HCL)
•MultielementHCL
•Demountable HCL
•High Intensity HCL
Electrodeless Discharge Lamp (EDL)
Temperature Gradient Lamp

31. Hollow Cathode Lamp
(Most popular)
Quartzwindow
Pyrexbody
Anode
Cathode

32. Filler Gas
(Ne or Ar)
at 1-2 Torr
W, Zr, Ni
Made up of
element of
interest or its
alloy
100-200 V
(1-25 mA)
Ar+
Ar
+
ions strike the cathode to cause Sputtering.
Why Low P?
Sputtering?
Disadvantage?
Multi-element HCL (2-7 elements)/Suffer
Composition change/More volatile
elements distills first and more, Caution!
Demountable HCL. Replaceable cathode,
but time/effort involved.
1 torr = 0.0013158 atm

33. HOW Hollow Cathode Lamp works?
a tungsten anode and a
cylindrical cathode
neon or argon at a pressure of 1
to 5 torr
The cathode is constructed of
the metal whose spectrum is
desired or served to support a
layer of that metal
Ionizetheinertgasatapotentialof~300V
Generateacurrentof~5to15mAasions
andelectronsmigratetotheelectrodes.
Thegaseouscationsacquireenoughkineticenergytodislodgesomeofthe
metalatomsfromthecathodesurfaceandproduceanatomiccloud.
Aportionofsputteredmetalatomsisinexcitedstatesandthusemitstheir
characteristicradiationastheyreturntothegroundsate
Eventually,themetalatomsdiffusebacktothecathodesurfaceortotheglass
wallsofthetubeandarere-deposited

34. Hollow Cathode Lamp (Cont’d)
High potential, and thus high currents lead to
greater intensities (Operators’ control) as more
sputtering occurs, BUT also leads to self-absorption
and resonant broading.
Self-absorption or Self-reversal:the greater currents
produce an increased number of unexcitedatoms in
the cloud. The unexcited atoms, in turn, are capable
of absorbing the radiation emitted by the excited
ones.Thisself-absorption leads to lowered
intensities, particular at the center of the emission
band
ResonanatBroading: Pressure broadening caused by
collision between identical atoms

35. Improvement…….High Intensity HCL
Most direct method of obtaining improved lamps
for the emission of more intense atomic resonance
lines is to separate the two functions involving the
production and excitation of atomic vapor
Boosted discharge hollow-cathode lamp (BDHCL)
or High Intensity HCL is introduced as an AFS*
excitation source by Sullivan and Walsh.
It has received a great deal of attention and a
number of modifications to this type of source have
been conducted.
*rarely used for AAS

36. Auxiliary electrode
(excitation)
Auxiliary electrode
(excitation)
CathodeAnode
30⎼100 times higher
Intensity than conventional
HCL, how?
Low current between Cathode and Anode keeps
Sputtering Low, Low atomic population
High potential and current between Auxiliary
electrodes keeps excitation high

37. Electrodeless Discharge Lamps (EDL)

38. Evacuated
quartz tube
= M or MX (~ 5 mg)
Construction of EDL
Avalible for
As, Bi, Cd, Cs, Ge, Hg, K, P,, Pb,
Rb, Ti, Zn

39. Operation of EDL
Constructed from a sealed quartz tube containing a few torr
(0.1-5 torr) of an inert gas such as argon and a small quantity
of the metal of interest (or its salt).
The vapourpressure of the elements used in EDL are
sufficiently high to permit some gaseous atoms of the
element to form in the low P environment of the lamp.
The lamp does not contain an electrode but instead is
energized by an intense field of radio-frequency or microwave
(2450 MHz) radiation.
Radiant intensities usually one or two orders of magnitude
greater than the normal HCLs. Mostly used for AFS.
The main drawbacks: their performance does not appear to
be as reliable as that of the HCL lamps (signal instability
with time) and they are only commercially available for some
elements only. Their Intensity depends on T so T controlled
required ; they are less stable than HCL.

40. Temperature Gradient Lamp
(AAS and AFS)
Intensity greater
than HCL
Emitted Linewidth
0.001 nm
An Electric heater converts element into atomic vapor.
Filler gas Ar
(1-5 torr)
Mostly used for
As and Se

41. Atomizer
Nebulizer Burner Flame

42. How to get samples into the
instruments?
AAS

43. How to get sample atomize?

44. What is a nebulizer?
(Breaks sample into fine mist)
SAMPLE
AEROSOL

45. Nebulizers
Controlled droplet size distribution
Uniform flow rate
Easy cleaning
No Blockage
No chemical reaction with solution

46. Pneumatic Nebulizers
Simplest, for clear non-turbid solutions
Break the sample solution into small droplets.
Solvent evaporates from many of the droplets.
Most (>99%) are collected as waste
The small fraction that reach the flame have been de-
solvated to a great extent.
Efficiency of Nebulizer (droplet size distribution)
depends on flow rate, viscosity, surface tension of
solvent
A corrosion-resistant bead placed at the outlet of the
nebulizer increase efficiency by removing big droplets.

47. Concentric Tube

48. Cross-flow

50. Fritted-disk

51. Babington
Viscous liquids
No Blockage

52. ULTRASONIC NEBULZIERS
Sample is placed in a tank and ultrasound waves
are passed through it from the base.
The dense fog formed is swept with an oxidants
into the flame.
Particle size distribution depends on frequencyand
is independent of flow rate of oxidant

53. How to get sample atomize?

54. BURNERS
Total Consumption Burner
Premix or Laminar-flow Burner

55. Total Consumption Burner
Fuel, Oxidant and Sample flow directly into the flame
No mixing of flame gases prior to being burned in
flame (Advantage!!!)
No risk of explosion and gases with high burning velocity
Can be used
Disadvantages:
Turbulent flame (erratic cooling caused by large droplets
Scattering by large droplets (incomplete vaporization)
Flame shape not ideal for AAS measurements (short
pathlength)
More sample enter the flame but efficiency of atomization
is low
TCB rarely used

56. Premix Burner
Turbulence decreases if large droplets are
Avoided.
Fuel is mixed with oxidant and sample (Risk!)
Only fine droplets reach the flame
Large droplets (90% sample) are drained out
(Disadvantage)
Less sample enter the flame but atomization is
efficient (advantage)
Longer pathlength (suitable burner head) (Advantage!)
Smoother burning flame results in high S/N ration (Better for Quantitative analysis!)

57. •Sample is “pulled” into the nebulization chamber by the flow of fuel
and oxidant.
Laminar Flow Burners
•Contains spoilers
(baffles) to allow only the
finest droplets to reach
the burner head.
•Burner head has a long
path length and is ideal
for atomic absorption
spectroscopy.

59. Advantages:
1. Uniform dropsize
2. Homogeneous flame
3. Quiet flame and a long path length
Disadvantages:
1. Flash back if V
burning> V
flow
2. ~90% of sample is lost
3. Large mixing volume

60. FLAMES
Rich in
free atoms
The sequence of events in not the same for every drop (drop size, Fuel/Oxd flow rate,
type of flame, oxides formation tendency

61. 1.Types of Flames
Fuel / Oxidant Temperature
H-CC-H acetylene / air2100 °C –2400 °C (most common)
acetylene / N
2O 2600 °C –2800 °C
acetylene / O
2 3050 °C –3150 °C
•Selection of flame type depends on the volatilization temperature of
the atom of interest.
2.Flame Structure
•Interzonal region is the hottest part of the
flame and best for atomic absorption.
•Fuel rich flames are best for atoms because
the likelihood of oxidation of the atoms is
reduced.
•Oxidation of the atoms occurs in the
secondary combustion zone where the atoms
will form molecular oxides and are dispersed
into the surroundings.

62. •A αƖand A αC
C of atoms in flam can be increased by decreasing volume.
Unfortunately, increasing Ɩincreases volume.
So then?
Use a burner head that gives long but thin/narrow flame
Toothin/narrowaflamecangetseasilycooledandatomic
populationmaydecrease,Caution!
TEMPRATUREofflamedependsonFUEL/OXD.Ratio
FUEL-RICHFLAME,morefuelthanoxidant,reducingbutlowT)
LEANFLAME:Oxidantrichflame(oxidizingbuthotter)

63. 3.Temperature Profiles
•It is important to focus the entrance slit of the
monochromator on the same part of the flame
for all calibration and sample measurements.
4.Flame Absorption Profiles
•Mg -atomized by longer exposure to
flame, but is eventually oxidized.
•Ag -slow to oxidize, the number of atoms
increases with flame height.
•Cr -oxidizes readily, highest
concentration of atoms at the base of
the flame.

64. FlameabsorbanceProfiles:
Fig.9-4showstypicalabsorption
profilesforthreeelements.
Magnesiumexhibitsamaximumin
absorbanceatthemiddleofthe
flame.Thebehaviorofsilver,
whichisnotreadilyoxidized,is
quitedifferent,acontinuous
increaseinthenumberofatoms,
andthustheabsorbance,is
observedfromthebasetothe
peripheryoftheflame.Chromium,
whichformsverystableoxides,
showsacontinuousdecreasein
absorbancebeginningclosetothe
burnertip.

65. Flame Burner
M
n+
(aq) + anion(aq) salt(s)
salt(s) salt(g)
salt(g) atoms (g)
M(g) + hnM*(g)

66. FLAMES

67. Types of Flames Used in Atomic
Spectroscopy

68. Ca Cu
K
Mn

69. Cold vapour technique (uheated cell)
Hg
2+
+ Sn
2+
= Hg + Sn (IV)
5% H
2SO4
+
0.05 M KMnO
4
Hg
lamp
253.7 nm
SnCl
2

70. Cold vapour technique (unheated cell)
Hg
2+
+ Sn
2+
= Hg + Sn (IV)

71. 71
Hydride generation methods
(HGAAS)
For arsenic (As), antimony (Te) and selenium (Se)
As
0
(gas)+ H
2As (V) AsH
3
NaBH
4
(sol)
heat
in flame[H
+
]
Thereactionofmanymetalloidswithsodiumborohydride
andHClproducesavolatilehydride:H
2Te,H
2Se,H
3As,
H
3Sb,etc.

72. 72
H
(HGAAS)

73. http://www.shsu.edu/~chm_tgc/sounds/flashfiles/HGAAS.scrubber.swf
(HGAAS)

74. http://www.shsu.edu/~chm_tgc/primers/primers.html
(HGAAS)

75. ElectrothermalAAS (ETAAS or GFAAS)
(Flameless atomizers)
Tubular graphite furnaces Carbon rod/cup atomizers
L’ vov, B.V.: Spectrochim. Acta, 17: 761 (1961)
Professor Boris Vladimirovich L’vov with
his wife after the award ceremony
(Fijalkowski award 2010)

76. ElectrothermalAAS (ETAAS or GFAAS)
(Flameless atomizers)
The sample is contained in a heated, graphite
furnace.
The furnace is heated (up to 3500°C) in a controlled
manner by passing an electrical current through it
(electro-thermal).
To prevent oxidation of the furnace, it is sheathed in
gas, Aror N
2(up to 2500°C (cyanogensformation!))
There is no nebulzation, etc. The sample is
introduced as a drop (usually 5-50 µL), slurry or
solid particle (rare)

77. The furnace goes through several steps.
Drying (usually just above 110 °C, 10 s)…Solvent evaporation
Ashing(350⎼1200 °C, 45 s)…Organic volatilized/matrix destroyed
Atomization (Up to 2000⎼ 3000 °C, 5 s)… Discrete gaseous atoms
formed and absorbance measured
Cleanout (quick ramp up to 3500 °C or so)… Waste is blown out with
a blast of Ar.
Heatingrateiskepthigh(1000°Cto10
8
°C)toensurehighatomic
concentrationduringatomization.Thelightfromthesource(HCL)passes
throughthefurnaceandabsorptionduringtheatomizationstepisrecorded
overseveralseconds.ThismakesETAASmoresensitivethanFAASfor
mostelements.
Steps involved in atomization process in Furnaces

78. Drying (usually just above 110 °C)
Ashing (350⎼1200 °C)
Atomization(Up to 2000⎼ 3000 °C)
Cleanout(quick ramp up to 3500 °C)
Steps involved in atomization process in Furnaces

79. Tubular Graphite Furnace
Tubular graphite furnace is often coated with pyrolytic graphite (less porous than graphite)
Drawbacks: Significant background absorption and matrix effect.
Matrix effect is eliminated by using a furnace that operates at constant temperature

80. Platform Tubular Graphite Furnace

82. Carbon Rod Atomizers
Not very famous
Cylindrical graphite rod/cup with a hole
Argon-sheathed (prevention of oxidation)
Temperature of sample point is high than
surrounding (avoids wastage of sample)

83. Inert-gas flow: stop gas flow at atomization step
Sample amount: adequate sample needed. Too much sample leads to
greater atomization and expulsion of vapours to surrounding (abs↓)
Organic compounds surrounding metallic analytes makes it difficult for
sample to get uniformly heated.
Carbides formation (Refractory!)
Cyanogen formation (N
2react with graphite above 2500°C)
Factors affecting atomization in Furnaces

84. Flames vs. Furnaces
Flames
Large sample volume
Sample stay shorter in flame
Furnaces
Small sample volume (5-50 µL)
Sample stay longer in path of EMR (can be used to
assay smaller sample volumes and lower concentrations
Expensive (power supply)
Extra care to get reproducible results
Background correction
Requires fast responding detector

85. Wavelength Selectors
Generally monochromator are used .
Band pass of monochromators: 0.2, 0.5, or 1 nm
Width of absorptive lines: 0.004 nm (narrower
than band pass of monochromator)

86. Amonochromatorsconsistsofentrance/exitslits,aprismor
diffractiongrating(dispersivecomponent)andlenses/mirrors
(tocollimate/focusthebeam).
Theygenerallyemployadiffractiongratingtodispersethe
radiationintoitscomponentwavelengths.Olderinstruments
usedprismsforthispurpose.
Monochromator
ByrotatingthegratingorPrism,differentwavelengthscanbemadetopass
throughanexitslit.Theoutputwavelengthofamonochromatoristhus
continuouslyvariableoveraconsiderablespectralrange
Prism monochromators
Grating
Monochro
-mators

87. Grating monochromator
Byrotatingthegrating,differentwavelengthscanbemadetopassthroughanexitslit.The
outputwavelengthofamonochromatoristhuscontinuouslyvariableoveraconsiderable
spectralrange.Thewavelengthrangepassedbyamonochromator,calledthespectral
bandpassoreffectivebandwidth,canbelessthan1nmformoderatelyexpensive
instrumentstograterthan20nmforinexpensivesystems.
The output of a grating monochrmomator
λ
2 < λ
1

88. Effective bandwidth-the width of the
band of transmitted radiation in λunits at half
the peak height.
For monochormators EBW = few 10th of a nm
For absorption Filter EBW = 200 nm or more
Transmittance at nominal λ
nominal λ

89. Photomultiplier Detector
PMT is commonly used.
The detector consists of a photoemissive
cathode coupled with a series of electron-
multiplying dynode stages, and usually called a
photomultiplier.
The primary electrons ejected from the photo-
cathode are accelerated by an electric field so as
to strike a small area on the first dynode.
Detectors
Amplification: n
d
n= average no. of e emitted by each dynode
d = number of dynodes

90. Photomultiplier Detector

91. Single-beam design

92. DOUBLE BEAM FAA
SPECTROMETER
Note: the Ref beam does not pass
through the flame thus does not correct for the
interferences fromthe flame!
synchronized

93. Interferences in AAS
1-Chemical Interferences
2-Ionization interferences
3-Spectral interferences
4-Matrix interferences

94. Chemical Interferences
Chemical reaction in cell (removal of atoms)
Formation of compounds of low volatility
Calcium analysis in the presence of Sulfate (CaO.SO
3) or
phosphate(CaO.P
2O
5)
Formations of refractory oxides (Al
2O
3, Fe
2O
3) of unusual stability
in flames
Formation of carbides or cyanogen(CN)
2in furnaces
Solutions
Higher temperature or deceases O
2 concentration (fuel rich
flame), e.g., changing air-C
2H
2flame to N
2O-C
2H
2flame
Releasing agents: Cations(e.gLaCl
3 used for Ca, Mg, Sr) hat
react preferentially with the interference ions.
(Ca
2+
(analyte)+ PO
4
3-
(interfering)+ La
3+
LaPO
4+ Ca
2
(free) )
Protection agents: form stable but volatile species with the
analytes (i.e. EDTA)

95. Ionization Interferences
Atom ionization (usually due to high T)
M ↔ M
+
+ e (group IA and IIA have low IE)

96. Spectral lines occur at different λthan atomic lines
-decrease in AA signal
Ionization decreases at high concentration
-competition B/W atom for available E
Solutions
Use low temperature flame (air-propane)
Add large amount of easily ionizing element
(500-5000 µg/mL of Li, Na, K) element
Use high concentration of analyte

98. Matrix interferences
These are caused by the physical nature of the matrix enhancing
or depressing sensitivity
Example: Viscosity difference b/w sample and stadards
(different nebulzation/aspiration/atomization)
Solutions
Standard addition technique
Matching the matrix of sample
with that of standards
Solvent extraction or so to
isolate the analyte

99. Spectral Interferences
Overlapping (spectra of analyteand another atomic/molecular
species)
Background (non-specific) Interferences :
-Spectral interferences resulting from emission of EMR
from elements in cell
-Scattering or absorption by sample matrix or polyatomic
species
Positive error (analyteand matrix absorb the same λ)
Negative error: Interfering species emits same λas used for
measurement
Tb/Mg = 285.2 nm
Cr/Os = 290.0 nm
Ca/Ge = 422.7 nm
Examples:

100. Spectral Interferences…
Solutions
Chemical Separation prior to the assay
Modulation of the detector
Background correction
Modulationofthedetector:
Thedetectoristunedtothefrequencyofoscillationofthe
EMRsource,itdoesn’trespondtothesteady-stateemissions
fromthecell.Therefore,interferenceowingtoemissionfrom
thecelliseliminated

101. Background Correction
Background (non-specific) Interferences:
-Spectral interferences resulting from emission of EMR
from elements in cell
-absorption by polyatomic species or scattering within the
cell
-More severe in furnaces than flames
-Greater at shorter λs (more scattering)

102. Continuum-Source Correction
Background Correction
A
HCL= A
analyte+ A
background
A
D2= A
background

103. Continuum-Source Correction

104. 0.04 nm
A
B
The light from the HCL is absorbed by both the sample and the background, but
the light from the D
2lamp is absorbed almost entirely by the background
A:HCL lamp, the shaded portion shows the light absorbed from the HCL. The emission
has a much narrower line width than the absorption line.
B: D2 lamp, the shaded portion shows the light absorbed from the D
2lamp. The lamp
emission is much broader than the sample absorption, and an averaged absorbancetaken
over the whole band pass of the monochromator.
(The draw is not to scale)

105. Quantitative analysis (AAS)
Beer’s Law is obeyed: A = kbC
Concentration in cellαconcentration in solution
(under fixed experimental condition)
AbsorbanceαConcentration in cell
Absorbanceαconcentration in solution
Thus
As
And
b = pathlength
C= concentration
k = constant representing molar
absorptivity and other factors that may
affect absorbance such as
aspiration rate, degree of atomization,
the position of flame where signal is
measured, flow rate of gases entering
the flame, T of cell
A working curve method or standard addition method can be used
for quantitative analysis

106. Sample Problem: pg. 312, #3
Lead is extracted from a sample of blood and analyzed at 283 nm and gave an
absorbance of 0.340 in an AA spectrometer. Using the data provided, graph a
calibration curve and find the concentration of lead ions in the blood sample.[Pb+2] (ppm)Absorbance Calculated Pb (II) concentraions (ppm)Absorbance
0.000 0.000 0.324 0.340
0.100 0.116
0.200 0.216
0.300 0.310
0.400 0.425
0.500 0.520
y = 1.0505x
R² = 0.9988
0.000
0.100
0.200
0.300
0.400
0.500
0.600
0.000 0.100 0.200 0.300 0.400 0.500 0.600
Absorbance
[Pb+2] (ppm)
Lead (II) Calibration Curve
•The data provided
in the problem
appears in the
upper left hand
corner of this MS
EXCEL worksheet.
•The graph was
used to calculate
the best fit line.
•The equation was
then used to
calculate the
concentration of
Pb (II) ions with an
absorbance of
0.340.
•The result, 0.324
ppm, is displayed
above the graph.

107. Elements detectable by atomic absorption are highlighted in pink in
this periodic table

108. Comparison Between Atomic
Absorption and Emission
Spectroscopy
Absorption
-Measure trace metal
concentrations in
complex matrices .
-Atomic absorption
depends upon the
number of ground state
atoms .
Emission
-Measure trace metal
concentrations in
complex matrices .
-Atomic emission depends
upon the number of
excited atoms .

109. -It measures the
radiation absorbed by
the ground state atoms.
-Presence of a light
source ( HCL ) .
-The temperature in
the atomizer is adjusted
to atomize the analyte
atoms in the ground
state only.
-It measures the
radiation emitted by
the excited atoms .
-Absence of the light
source .
-The temperature in the
atomizer is big enough
to atomize the analyte
atoms and excite them
to a higher energy level.

110. 3
AAS APPLICATIONS
The are many applications for atomic
absorption:
-Clinical analysis : Analyzing metals in
biological fluids such as blood and urine.
-Environmental analysis : Monitoring our
environment –e g finding out the levels of
various elements in rivers, seawater,
drinking water, air, and petrol.

111. -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.

112. -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 –e g in concrete, where calcium is a major
constituent, the lead level should be low because it is
toxic.

113. -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 .
-Trace elements in food analysis
-Trace element analysis of cosmetics
-Trace element analysis of hair

114. Paper 1
Determination of lead in dialysis
concentrates using FI –HG AAS
-Dialysis is a medical treatment that is given to patients with
abnormal function of the kidney .
-Washing the kidney from the various trace elements that the
kidney itself should have done .
--One of the elements that is present in a dialysis concentrate is
lead ,which is very toxic and become fatal if it exceeds the level of 380
กg/ l in our body .
--In order to determine the Pbconcentration in a dialysis
concentrate, a flow injection hydride generation atomic
absorption spectroscopy was proposed .

115. -The hydride generation is very applicable since its is a
reducing agent and for some metals with high
oxidation state the atomization energy is high, so the
hydride simply reduces the oxidation sate and thus the
atomization energy .
-Lead hydride is usually unstable but in an acidic medium of
HClwith the presence of a mild oxidant K
3Fe (CN )
6, it
showed high precision and freedom from
interferences .

116. -Sample is injected in an HCl, K
3Fe (CN )
6 carrier
solution and then combined with withNaBH4 to mix
in the mixing coil .
-An Argon gas carrier is used to sweep out the lead
hydride carrier all the way to the atomizer .
-Comparison was done with an electro thermal AAS ,and
the results were close but in FI HG AAS interference
was absent .
-Finally FI HG AAS showed to be easy, simple ,and low
cost compared to ICP; and it is applicable to all
hydride standards .

117. paper 2
Online separation for the speciation of
mercury in natural waters by flow injection
Atomic Absorption Spectrometry ratio
-Nowadays methyl mercury is considered as the
most toxic mercury compound .
-In this application separation of inorganic
mercury Hg
+
from methyl mercury CH
3Hg
+
will
be performed in an ion exchanger in a FIA
apparatus, and then followed by detection of
CH
3Hg
+
in an atomic absorption spectrometer .

118. -An ion exchanger is used to take out the Hg+
since at pH < 10 Hg+ is completely anionic
(HgCl)4-2 while CH3HgCl remains neutral .
-The left CH3Hgcl is detected by an atomic
absorption Spectrometer .
-This application is very interesting because it
used AAS , and FIA techniques to do both
separation and detection .

119. Supplementary Slides

120. Line Broadening
Uncertainty Effects
Heisenberg uncertainty principle:
The nature of the matter places limits on the
precision with which certain pairs of physical
measurements (complementary variables) can be
made.
One of the important forms Heisenberg uncertainty
principle:
tn≥ 1
To determinenwith negligibly small uncertainty, a huge measurement time
is required.
Natural line width

122. INTERFERENCES IN ATOMIC
ABSORPTION SPECTROSCOPY
1.SpectralInterferences:
(I)Spectralinterferencecanoccurduetooverlapping
lines.e.g.avanadiumlineat3082.11Åinterferesinan
analysisbaseduponthealuminumabsorptionlineat
3082.15Å.Thistypeofinterferencecanbeavoidby
employingthealuminumlineat3092.7Åinstead.
(II)Spectralinterferencesresultfromthepresenceof
combustionproductsthatexhibitbroadbandabsorption
orparticulateproductsthatscatterradiation.Both
diminishthepowerofthetransmittedbeam.Ablank
canbeaspiratedintotheflametomakethecorrection.

123. …SpectralInterferencescontinued…
(III)Sourceofabsorptionorscatteringcan
beoriginatedinthesamplematrix.An
exampleofapotentialmatrixinterference
duetoabsorptionoccursinthe
determinationofbariuminalkalineearth
mixture.ThewavelengthofBalineusedfor
atomicabsorptionanalysisappearsinthe
centerofabroadabsorptionbandfor
CaOH.Theeffectcanbeeliminatedby
substitutingnitrousoxideforairasthe
oxidantwhichyieldsahighertemperature
thatdecomposedtheCaOHandeliminates
theabsorptionband.

125. …SpectralInterferencescontinued…
(IV)Concentratedsolutionofelements
suchasTi,ZrandWwhichform
refractoryoxidescancausespectral
interferenceduetoscattering.
(V)Organicsolventororganicimpurities
inthesamplecancausescattering
interferencefromcarbonaceousparticle
becauseofincompletecombustionofthe
organicmatrix.

126. 2.ChemicalInterferences:
(I)FormationofCompoundsofLow
Volatility:Themostcommontypeof
interferenceisbyanionsthatformcompounds
oflowvolatilitywiththeanalyteandthus
reducetherateatwhichtheanalyteisatomized.
Thedecreaseincalciumabsorbancethatis
observedwithincreasingconcentrationsof
sulfateorphosphate.Exampleofcation
interferencehavealsobeenrecognized.
Aluminumisfoundtocauselowresultsinthe
determinationofmagnesium,apparentlyasa
resultoftheformationofaheat-stable
aluminum/magnesiumcompound.

127. …Formation of Compounds of Low Volatility
continued…
Interferenceduetoformationofspeciesoflow
volatilitycanoftenbeeliminatedormoderated
byuseofhighertemperatures.Releasing
agentswhicharecationsthatreact
preferentiallywiththeinterferantandprevent
itsinteractionwiththeanalyte,canbe
employed.Protectiveagentsprevent
interferencebyformingstablebutvolatile
specieswiththeanalyte.Threecommon
reagentsforthispurposeareEDTA,8-
hydroxyquinoline,andAPDC(ammoniumsalt

128. …Chemical Interferences continued…
(II)DissociationEquilibria:Gaseous
environmentofaflameorafurnace,numerous
dissociationandassociationreactionsleadto
conversionofthemetallicconstituentstothe
elementalstate.Someofthesereactionsare
reversible
MO M + O
M(OH)
2 M + 2OH
Where M is the analyte atom.
VO
x V + O
x
AlO
x Al + O
x
TiO
x Ti + O
x

129. …ChemicalInterferencescontinued…
(III)IonizationEquilibria:Ionizationof
atomsandmoleculesissmallincombustion
mixturesthatinvolveairastheoxidant,and
generallycanbeneglected.Inhigher
temperaturesofflameswhereoxygenornitrous
oxideservesastheoxidant,however,ionization
becomesimportant,andasignificant
concentrationoffreeelectronsexistsasa
consequenceoftheequilibrium
M M
+
+e
-
TheequilibriumconstantKforthisreaction
takestheform
K=[M
+
][e
-
]
[M]