ATOMIC ABSORPTION SPECTROSCOPY

HISTORY
The beautiful phenomenon of “RAINBOW”
was the first dispersed spectrum.

In 1665 NEWTON took the first and the most important step
towards the development of spectroscopy.

In 1859 G.R KIRCHOFF and R BUNSEN emerged as the FATHER
OF MODERN SPECTROSCOPY.

SPECTROSCOPY
The study of structure of atom or molecules.
Used in analysis of wide range of sample
Can classify in atomic or molecular spectroscopy.

ATOMIC SPETROCOPY

MOLECULAR SPECTROSCOPY

ABSORPTION SPECTROSCOPY
• It gives the measurement of absorbed energy by the
atom or molecule after which it excite and gives the
absorbed energy in the form of absorption spectrum

ATOMIC ABSORPTION SPECTROSCOPY
• Atomic absorption spectroscopy is a technique for
determining the concentration of a particular metal
element in a sample. Atomic absorption
spectroscopy can be used to analyze the
concentration of over 62 different metals in a
solution.

TYPES OF ATOMIC SPECTRA
1) ATOMIC EMISSION SPECTRA:

3) ATOMIC FLUORESCENCE SPECTRA

COMPARISON

ATOMIC EMISSION ATOMIC ABSORPTION
SPECTROSCOPY SPECTROSCPY
• Examines the wavelengths of • Measures the loss of
photons emitted by atoms or electromagnetic energy after it
molecules during their transition illuminates the sample under
from an excited state to a lower study.
energy state. • The energy in certain amount
• Each element emits a is absorbed during transition
characteristic set of discrete to the higher level.
wavelengths. • The amount of energy
• By observing these wavelengths absorbed gives estimate of the
the elemental composition of concentration of the analyte in
the sample can be determined. the sample.

PRESENTORS:

RIMSHA ISMAIL (11780)
RUTABA MURTAZA (11782)

THEORY OF ATOMIC ABSORPTION
SPECTROSCOPY

• Absorption therefore is carried out by unexcited atoms.

CONCEPT OF ATOMIC ABSORPTION
SPECTROSCOPY
• In 1955, A. WALSH and another one of C T J ALKAMADE and J M W
MILATZ.

PRINCIPLE OF ATOMIC ABSORPTION SPECTROSCOPY
EVAPORATION VAPORIZATION
SOURCE SOLUTION MIST

DISSOCIATION GAS SOLID

hv
THERMAL FLAME
EXCITATION EMISSION

hv2 RE-EMISSION
ABSORPTION OF
RADIANTENERG (FLUORESCENCE)
Y

RECORDER DETCETOR MONOCHROM
AMPLIFIER ATER

• The total amount of light absorbed may be given mathematically by the
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

INSTRUMENTATION OF ATOMIC
ABSORPTION SPECTROSCOPY

1. RADIATION SOURCE

The main sources used for atomic absorption are:
I. Hollow Cathode Lamp (HCL)
II. Electrode less Discharge Lamp (EDL)

II. ELECTRODELESS DISCHARGE
LAMP

2. ATOMIZERS

There are two types of atomizers which
are used in Atomic Absorption
Spectroscopy.
• Flame Atomizers
• Electrothermal Atomizers

FLAME ATOMIZER:
• Flame is used to atomize the sample
• Sample when heated is broken into its atoms

PRINCIPLE:
• High temperature of flame causes excitation
• Electrons of the atomized sample are promoted to higher
orbitals, by absorbing certain amount of energy

QUANTITATIVE ANALYSIS:
• The amount of energy absorbed is specific for a particular element
(for electronic transition).
• Amount of absorbed radiation is a quantitative measure for the
concentration of the element to be analyzed

SAMPLE NEBULIZER
ASSEMBLY
FLAME
(ATOMIZATION
OCCURS)

CONVERSION
INTO FINE MIST
AEROSOL
& SMALL
MIXES WITH
DROPLETS OF
COMBUSTION
SOLUTION
GASES
ASPIRATED
INTO SPRAY
CHAMBER
(MIXING
CHAMBER)

Sample to be Nebulizer:
nebulized is
sample+fuel+
taken
(aspirated) oxidant
via a capillary fine mist or
tube aerosol

Natural Gas Air 1700-1900 39-43

Natural Gas Oxygen 2700-2800 370-390

Hydrogen Air 2000-2100 300-440

Hydrogen Oxygen 2550-2700 900-1400

Acetylene Air 2100-2400 158-266

Acetylene Oxygen 3050-3150 1100-2480

Acetylene Nitrous Oxide 2600-2800 285

- Wavelength selectors
- Produces
monochromatic light

Consists of:
1) Entrance slit
2) Diffraction grating
3) Exit slit

Diffraction gratings are
mostly used rather than
prisms

Electro thermal atomization (ETA) (also known
as Graphite furnace atomization)

Used for improvement and betterment in the limit-
of-detection and sensitivity for atomic absorption
measurements.

Graphite tube

Enclosed water
cooled housing
Transparent
windows
Inert purge gas
control
Electrical contact

1.Drying

Atomization 2. Ashing or
of sample pyrolysis

3.Atomization

WORKING OF PHOTOMULTIPLIER TUBE

The signal could be displayed for readout in the readout devices.

Readout
devices:
• Digital voltmeter
• Simple galvanometer
• Potentiometer
• Computer

• Atomic Absorption spectrophotometric measurements are
done extensively by using;
 Single-Beam AA Spectrophotometer
 Double-Beam AA Spectrophotometer

• 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.

Single Beam AA Spectrophotometer:

Single beam measurements are 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.

Double Beam AA Spectrophotometer:

• It split the light from the source into a ‘sample beam’
(focused to the sample cell) and a ‘reference beam’ (focused
around the sample cell).
• 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.

Single Beam Instruments Double Beam Instruments
 Simple, Less expensive, less complexity  Complex, more expensive, not easily made

 Low automation, more efficiency of light  High speed automation, less light efficiency

 More time consuming  Less time consuming

 Low stability  Increased stability

 Depend upon single beam intensity  Depend upon ratio between both beams

 More chances of fluctuations  Lesser fluctuations in readings

Sample and Reference placed separately  Sample and Reference are kept at same
time
High light throughput, more resolution  Less light throughput, decreased resolution

More warm-up time is required Less or reduced warm-up time required

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

• A sample employed for atomic absorption spectroscopy in the
laboratory is placed into one of the following categories:
• Considerations are to be given to
some of the general principles involved
in the various sample preparations.

• 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.

• 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 ‘BURNER
CONTROLS’, proper ventilation or other
appropriate settings must be used.

• 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.

• 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).

• Atomic absorption analytical works
or procedures can be employed in
analyzing gases indirectly as
liquid sample.
PREPARATION:

Separate metals Using Millipore Wash or
from gas filter disc dissolve

Analyze using
Using nitric acid
standards

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:

Undissolved in
Inorganic samples Treated with acids
aqueous solvents

Clean liquid with no
Such as Perchloric Digestion of
single element
acid, HCl, HNO3, complexes, silicates
being removed

Dry Ashing:
Heated in Mix left Remove inorganic
Weighed
furnace over in particles like lead
sample or mercury
(muffle) acid

Microwave Dissolution: (type of digestion)

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,

• 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

“Increase or decrease in the size of the signal
obtained from the analyte as a result of the
presence of some other known or unknown
component in the sample”
Types of interference:
 Spectral interference
Chemical interference

Spectral interference
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.

Examples of spectral interferences

Chemical interference

Formation of compound
of low volatility

Decrease in calcium
absorbance is observed
with increasing
concentration of sulfate
or phosphate

 By increasing flame temperature
Use of releasing agents (La 3+ )
Cations react with the interferent releasing
the analyte
Use of protective agents:
They form stable but volatile compounds with
analyte.

Ionization interference
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)

Influence of potassium on the
ionization of barium

ATOMIC ABSORPTION SPECTROSCOPY

 Pharmaceutical

 Biological

 Biochemical

For detection of purity and
consistency of these trace metals

Also for quantitative determination
of metals mainly in solid sample as
mineral, ores and alloys

• Magnesium in cast iron

• Silver, Zinc, Copper and Lead in
Cadmium metal

• Method of multiple standard addition
• A plot of absorbance against the amount
of standard can be used to determine the
amount of copper in a sample.

 Determination of trace metal in a silicon foam cavity wound dressing

 Zinc in Zinc insulin suspension and tetracosactrin Zinc
injection

 Copper and Iron in ascorbic acid

 Aluminum in albumin solution and Ca, Mg,
Mercury

 Zinc in water used for diluting haemodialysis solution

•For the analysis of pharmaceutically or therapeutically
essential component of formulation, such as Zinc in Zinc-
insulin, minerals in multivitamin-mineral preparation and
Ca, Mg, Al in antacids.

•To establish concentration limits where the metal is
regarded as an impurity.

•Mining industries

•Petroleum industries

•Determination of metallic elements in
food industry like Copper, Zinc and Nickel
in vegetable oil and copper in beer.

ATOMIC ABSORPTION SPECTROSCOPY

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