1. 1
Dr. D. Visagaperumal
Professor and Head
Department of Pharmaceutical Chemistry
T.John College of Pharmacy
Bangalore-83.
Email: chemistryvishak@gmail.com10/18/2020
3. Atomic absorption is a very common for detecting metals and
metalloidsin a samples.
It is very reliable and simple to use.
It can analyse over 62 elements.
It also measure the concentrationof metals in the sample.
INTRODUCTION
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4. The first atomic absorption spectrometer was built by the CSIRO
(Commonwealth Scientific and Industrial Research Organisation)
scientist Alan Walsh in 1954.
HISTOR
Y
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5. PRINCIPLE
When a beam of monochromatic radiation is passed through the atoms of
an element, the rate of decrease of intensity of radiation is proportional to the
intensity of incident radiation as well as the concentration of the solution.
This technique basically uses the principle that free atoms (gas) generated
in an atomizer can absorb radiation at specific frequency.
The atoms absorb UV or visible light and make transitions to higher
electronic levels. AAS quantifies the absorption of ground state atoms in the
gaseous state.
The analyte concentation is calculated from the amount of absorption.
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6. • The total amount of light absorbed may be given
mathematically bythe following expressions:
Total number of light absorbed = πe2/mc Nf
Where,
e = is the charge on the electron of mass
m= mass of electron
c= is the speed of light
N= is the total number of atoms that can absorb at
frequency in the light path
v= frequency
f= is the oscillator strength or ability of each atom to absorb
at frequency
π= is constant
The above equation can be written as:
Total amount of light absorbed= Constant x N x f
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18. HCL is the most common radiation source in AAS.
It contains a tungsten anode and a hollow
cylindrical cathode made of the element to be
determined.
These are sealed in a glass tube filled with an
inert gas (neon, argon).
Each element has its own unique lamp
which must be used for that analysis.
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19. Disadvantages of HCL:
oA finite lifetime-due to depletion of the analyte element from the cathode.
oAdsorption of fill gas atoms onto the inner surfaces of the lamp-the primary
cause for lamp failure.
oSome cathode materials can slowly evolve hydrogen when heated- a
background continuum emission contaminates the purity of the lines spectrum
of the element, resulting in a reduction of atomic absorption sensitivity and
poor calibration linearity.
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21. A small amount of the metal or salt of the element for which the
source is to be used is sealed inside a quartz bulb.
This bulb is placed inside a small, self-contained RF generator or
“driver”. When power is applied to the driver, an RF field is created.
The coupled energy will vaporize and excite the atom inside the
bulb causing them to emit their characteristic spectrum.
They are typically much more intense and, in some cases, more
sensitive than comparable HCL. Hence better precision and lower
detection limits where an analysis is intensity limited.
EDL are available for a wide variety of elements, including
Sb, As, Bi, Cd, Cs, Ge, Pb, Hg, P, K, Rb, Se, Te, Th, Sn and Zn.
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ELECTRODELESS DISCHARGE LAMP
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25. Some well known fuels with oxidants are
Air Propane 2200 K
Oxygen – Hydrogen 2450 K
Oxygen – Acetylene 2800K
Nitrous oxide – Acetylene 3230K
FUELS WITH OXIDANTSFLAME STRUCTURE 25
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26. POTENTIAL ADVANTAGES OF FLAMELESS
VAPORIZATION:
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(1)The elimination of anomalous results arising from interactions
between the sample and components of the flame.
(2)Increased sensitivityarising from a longer residencetime within the beam
of radiationfrom thelamp.
(3)Residence times in flames are low because of strong vertical
thermalcurrents.10/18/2020
27. (4) Increased sensitivity because of a higher proportion ofthe analyte
being converted to freeatoms.
(The conversion may be as low as 0.1% for flameatomization.)
(5) The ability to handle very small samples such as clinical
specimens.
(A nebulizer, spray chamber, burner arrangement consumes several
cm3 of sample per minute, most of which runs towaste).
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29. Sample Atomization Technique
Flame
Atomization
Electro thermal
Atomization
Hydride
Atomization
Cold-Vapor
Atomization
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 .
Atomization
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31. Flame Atomization
• Nebulizer suck up liquid samples at controlled rate.
• Create a fine aerosol spray for introduction into flame.
• Mix the aerosol and fuel and oxidant thoroughly for introduction into
flame.
• An aerosol is a colloid of fine solid particles or liquid droplets, in air
or another gas.
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34. Disadvantages of FlameAtomization
• Only 5-15% of the nebulized sample reaches the flame.
• A minimum sample volume of 0.5-1.0 ml is needed to
give a reliablereading.
• Samples which areviscous require dilution with asolvent.
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ELECTROTHERMALEVAPORATOR
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There is no nebulization, etc. The sample is introduced as a drop (usually
10-50 uL)
The furnace goes through several steps:
a. Drying (usually just above 110 deg. C.)
b. Ashing (up to 1000 deg. C)
c. Atomization (Up to 2000-3000 C)
d. Cleanout (up to 3500 C or so). Waste isblown out with a blast of
Ar.
36. Electro ThermalAtomization
• 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 vaporizeand atomize the analyte.
• The graphite tubes areheated using a high current power supply.
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39. Advantages and Disadvantages of GraphiteFurnace
Technique
Advantages
• Small samplesize
• Verylittle or no sample preparation is needed
• Sensitivity is enhanced
• Directanalysis of solidsamples
Disadvantages
• Analyte may be lost at the ashing stage
• The sample may not be completely atomized
• The precisionis poor than flamemethod
• Analytical range is relatively low 39
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40. Samples are reacted in an external system witha reducing agent,
usually NaBH4.
Gaseous reaction products(volatile hydrides)are then carried to a
sampling cell in the light pathof the AA spectrometer.
To dissociate the hydride gas into free atoms,the sample cell must be
heated.
The cell is either heated by an air-acetyleneflame or by electricity.
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HYDRIDE GENERATION
TECHNIQUE
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- Wavelength selectors
- Produces
monochromatic light
Consists of:
1) Entrance slit
2) Diffraction grating
3) Exit slit
Diffraction gratings are
mostly used rather than
prisms
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43. The intensity of the light is fairly low, so a photomultiplier tube
(PMT) is used to boost the signal intensity
A detector (a special type of transducer) is used to generate voltage from
the impingementofelectrons generated by the photomultiplier tube
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DETECTOR
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44. • Atomic Absorption spectrophotometric measurements are done
extensively by using;
Single-Beam AASpectrophotometer
Double-BeamAA Spectrophotometer
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45. • The first AAS was presented by Walsh and co-workers in Melbourne in 1954,
was a double beam atomic absorption spectrophotometer.
• Walsh worked with Perkin-Elmer, the first AAS instrument developed by that
company was MODEL 303.
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46. Single Beam AA Spectrophotometer
Single beam measurementsare depended upon the varying intensity of a single
beam of light having a single optical path. That is why called as single beam AA
spectrophotometer.
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47. Double Beam AA Spectrophotometer:
• It split the light from the source into a ‘sample beam’ (focused to the sample cell)
and a ‘referencebeam’ (focused around the samplecell).
• Such an instrument is called as double beam AA spectrophotometer, as
measurements are made on varying intensity of double beams of light in dual
optical path.
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50. Single Beam Instruments Double Beam Instruments
Simple, Less expensive, lesscomplexity
Low automation, more efficiency of light
More time consuming
Low stability
Depend upon single beamintensity
More chances of fluctuations
Sample and Reference placedseparately
High light throughput, more resolution
More warm-up time is required
Complex, more expensive, not easilymade
High speed automation, less lightefficiency
Less time consuming
Increased stability
Depend upon ratio between bothbeams
Lesser fluctuations in readings
Sample and Reference are kept at same
time
Less light throughput, decreasedresolution
Less or reduced warm-up time required
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51. SAMPLE PREPARATION
The preparation of the sample solution for a solid material is
most time consuming step of process of analysis in an atomic
absorption spectroscopy. It involves following steps;
Weighing of sample
Dissolution in appropriate solvent or
digestion using different techniques
Dilution of sample if necessary
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52. • A sample employed for atomic absorption spectroscopy in the laboratory is placed intoone
of the following categories:
• Considerations are to be given to some of the general
principles involved in the various samplepreparations.
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53. • A little preparation is required with this sort of sample.
• These include samples in raw and treated water, sea
waters, biological fluids, beer, plating
solutions, effluents, wines etc.
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54. • It include petroleum products, many of which can be directly
be aspired. Examples of such solvents used are m-
heptene, aliphatic ketones, (e.g. methyl iso butyl ketone)
aliphatic esters, alcohols and
xylene, cyclohexanes, isopropanol etc. are frequently
employed.
• Note: When samples are analyzed in organic solvents
some adjustments such as ‘BURNERCONTROLS’,
proper ventilation or other appropriate settings must
be used.
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55. • These include solid samples of fertilizers, ceramics, alloys or rocks.
• These are solvated by using appropriate aqueous or acid medium
depending on solubility. Such as hot water, concentrated acids,
acidic mixtures, dilute acids etc.
• Other techniques can also be employed such as fusion prolonged
acid digestion, wet ashing etc to yield sample solutions.
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56. • These includes typically material of foods, leaves, tissue, biological
solids, polymers, plants, feedstuff etc.
• Before solublization of such samples, there is a requirement of
destruction via wet digestion or ashing in a furnace (muffle).
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57. •Atomic absorption analytical works
or procedures can be employed in
analyzing gases indirectly as
liquid sample.
PREPARATION:
Separate metals
from gas
Using Millipore
filter disc
Wash or
dissolve
Using nitric acid
Analyze using
standards
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58. Techniques Used For Certain Sample Preparations:
• As discussed in previous topics, some solid sample requires
special techniques for dissolution. Such sample preparation
requires time and proper handling.
Wet Ashing Or Wet Digestion:
Inorganic samples
Undissolved in
aqueous solvents
Treated with acids
Such as Perchloric
acid, HCl, HNO3,
Digestion of
complexes, silicates
Clean liquid withno
single element
being removed
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60. Extraction and Concentration process:
• Such an operation is done if sample contain species
interfering in absorption or the concentration of sample
desired is in low concentration to show absorption readings.
Such a process involves,
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61. •The viscosity adjustment can be done
with suitable solvents which can be that
in a way solvent should;
o Dissolve or mix completely with the sample
o Well burnt but in a controlled manner
o Be in pure state such that possessing no species having
molecular absorption in region
o Not yield harmful by-products
o Not be expensive
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63. INTERFERENCES &
CONTROL MEASURES
NON SPECTRAL
Matrix
Method of
Standard
Additions
Chemical
add an excess
of another
element or
compound
which
will form a
thermally
stable
compound
with the
interferent
using a
hotter
flame.
Ionization
adding an
excess of
an
element
which
is very
easily
ionized
SPECTRAL
Background
Absorption
Continuum
Source
Background
Correction
Zeeman
Background
Correction
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64. This may be caused by direct overlap of the analytical line
with the absorption line of the matrix element.
HOW TO OVERCOME ?
By choosing an alternate analytical wavelength
By removing the interfering element from the sample.
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SPECTRAL INTERFERENCE
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65. Formation of compound of low volatility
Decrease in calcium absorbance is observed with increasing c
oncentration of sulfate or phosphate.
HOW TO OVERCOME
By increasing flame temperature
Use of releasing agents (La 3+ )
Cations react with the interferentreleasing the analyte
Use of protective agents:
They form stable but volatile compounds with analyte. 65
CHEMICAL INTERFERENCE
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66. Ionization of ground state gaseous atom with in a flame
will reduce extent of absorption in AAS.
M ↔ M+ + e-
HOW TO MINIMIZE:
Low temperature of the flame
Addition of an excess of ionization suppressant e.g. the
alkali metals (K, Na, Rb, and Cs)
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IONIZATION INTERFERENCE
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1. High selectivity and sensitivity
2. Fast and simple working
3. Solutions, slurries and solid samples can be analysed.
4. Smaller quantities of sample (typically 5 – 50 μL)
5. Provides a reducing environment for easily oxidized elements
6. Doesn’t need metals separation
7. Specific because the atom of a particular element can only absorb
radiation of their own characteristic wavelength
Disadvantages
1. Low precision and Low sample throughput
2. Can’t used for elements that give rise to oxides in flames
3. Limit types of cathode lamp (expensive).
4. Requires high level of operator skill
5. Sample must be in solution or at least volatile
6. Individual source lamps required for each element
ADVANTAGES AND DISADVANTAGES
Advantages
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68. APPLICATIONS OF AAS
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Atomic absorption spectroscopy is one of the most widely used
techniques for the determination of metals at trace levels in solution
Its popularity as compared with that of flame emission is due to its
relative freedom from interferences by inter – element effects and its
relative insensitivity to various in flame temperature
Only for the routine determination of alkali and alkaline earth metals ,
is flame photometry usually preferred
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69. Over sixty elements can be determined in almost in any matrix by
atomic absorption .
Ex: 1. Heavy metals in body fluids
2. Polluted waters
3. Food stuffs
4. Soft drinks and beer
5. Analysis of metallurgical and geochemical samples
6. Determination of many metals in soils, crude oils,
petroleum products and plastics etc
PURIFICATION OF WATER
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PETROLEUM PRODUCTS FOOD STUFF10/18/2020
70. Detection limits generally lie in the range 100- 0.1 ppb but these
can be improved by chemical pre – concentration procedures
involving solvent extraction or ion exchange
Currently a balance seems to have reached in the use of various
techniques for the determination of metals at trace levels
In its modern form AAS remains important and competative
where small ranges of elemants need to be determined in samples
Peak – Peak
noisecurve
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71. COMPARIS
ON
ATOMIC EMISSION
SPECTROSCOPY
• Examines the wavelengths of
photons emitted by atoms or
molecules during their transition
from an excited state to a lower
energy state.
• Each element emits a
characteristic set of discrete
wavelengths.
• By observing these wavelengths
the elemental composition of the
sample can be determined.
ATOMIC ABSORPTION
SPECTROSCPY
• Measures the loss of
electromagnetic energy after it
illuminates the sample under study.
• The energy in certain amount is
absorbed during transition to the
higher level.
• The amount of energy absorbed
gives estimate of the concentration
of the analyte in the sample.
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