Atomic absorption spectrometry (aas)

ABU DARDA
ZHCET-AMU

1. Atomic
Absorption
Spectrometry
(AAS)
ABU DARDA
M.Sc.(polymer science and technology)

2. Contents
•What is AAS
•Theory
•Instrumentations
•Principle of AAS
•Applications

3. What is AAS ?
Atomic absorption spectroscopy is a quantitative
method of analysis that is applicable to many metals
and a few nonmetals.
The technique was introduced in 1955 by Walsh
in Australia (A.Walsh, Spectrochim. Acta, 1955,
7, 108)
The application of
atomic absorption
spectra to chemical
analysis
Concentrations range is
in the low mg/L (ppm)
range.

4. Theory
A much larger number of the gaseous metal atoms
will normally remain in the ground state.
These ground state atoms are capable of absorbing
radiant energy of their own specific resonance
wavelength.
If light of the resonance wavelength is passed through a
flame containing the atoms in question, then part of the
light will be absorbed.
The extend of absorption will be proportional to the
number of ground state atoms present in the flame.

5. the gaseous metal atoms
specific resonance wavelength
the extend of absorption vs the number of ground state atoms
present in the flame.
extend of absorption

6. AAS Instrument

7. The simple diagram for the AAS
1. We set the
instrument at certain
wavelength suitable
for a certain element
2. The element
in the sample
will be atomized
by heat
3. A beam of UV light
will be focused on the
sample
5. The monochromator
isolates the line of
interest
4. The element in the sample
will absorb some of the light,
thus reducing its intensity
6. The detector
measures the change
in intensity
7. A computer data system
converts the change in
intensity into an
absorbance

8. Processes occurring during atomization
Flame atomization

9. Nebuliser - burner
To convert the test solution to gaseous atoms
Nebuliser --- to produce a mist or aerosol of the
test solution
Burner head --- The flame path is about 10 –12 cm
Vaporising chamber ---
Fine mist is mixed with the fuel gas and the carrier gas
Larger droplets of liquid fall out from the gas stream and
discharged to waste

10. 1. Nebulizer:
1. mixes acetylene (the fuel)
and oxidant
(air or nitrous oxide).
2. A negative pressure is formed at
the end of the small diameter,
plastic nebulizer tube®
(aspiration).
3. The result is a heterogeneous
mixture of gases (fuel + oxidant) and
suspended aerosol (finely dispersed
sample).
4. The mixture flows
immediately into the burner
head.
5. It burns as a smooth,
laminar flame evenly
distributed along a narrow
slot.
6. Liquid sample not flowing
into the flame collects in the
waste.
Note:
When do we use NO2 ?

11. Elements that are highlighted in pink
are detectable by AAS

12. Principle of Atomic Absorption
Spectrophotometer
Atomized elements each absorb energy of
a wavelength that is peculiar to that
element. The atomic absorption method
uses as its light source a hollow cathode
lamp which emits light of a wavelength that
is peculiar to each element. Elements
within a solution are heated in a flame or
electrically (2000K to 3000K) and
subsequently determined using the fact
that the degree of absorption will vary with
its concentration.
Light absorption
process of atoms

13. Atomic Absorption Spectroscopy, AAS
Atomic Emission Spectroscopy, AES
Principle of Atomic Absorption
Spectrophotometer
Ground state E
0
Excited state E
1
e
Absorption
Ground state E
0
Excited state E
1
e
Emission
ee

14. K
0
- maximal absorption
coefficient

Δ
n - half width
n
0
-central wavelength
Characters of the atomic absorption spectrum
Profile of the absorption line

15. I
t
= I
0ν
e
-Kνl
The relationship between absorbance The relationship between absorbance
and the concentration of atomsand the concentration of atoms
A = log （ II
0ν0ν/ / I
t
）= 0.4343 K
n
l
Beer’s law
I
t
- intensity of the transmitted light
I
o
– intensity of the incident light signal
l – the path length through the flame (cm)

16. Dilution
Dilute the sample with purified water, dilute acid, or organic solvents.
Examples: food products (e.g., dairy products), pharmaceuticals, and biological
samples (e.g., blood, urine).
Types of Pretreatment
Dry Decomposition
Heat the sample to a high temperature (400 to 500°C), Decomposition is possible
in a short time (a few hours) and operation is simple.
Elements with low boiling points (e.g., Hg, As, Se, Te, and Sb) will vaporize
Wet Decomposition
Heat the sample together with acid to a low temperature (approx. 300°C). Suitable for
volatile elements.
A long time is required for the decomposition of organic substances.
Microwave Decomposition
Decompose the sample at high pressure by heating it together with acid to a
temperature in the range 100 to 200°C in a sealed Teflon container.
The decomposition process is sealed; there is little vaporization of elements with low
boiling points; the decomposition time is short; there is little contamination from the
operating environment and the reagent; and only a small amount of acid is required.
Examples: Sediment, soil, dust, ceramics, living organisms, food products, etc.

17. Natural broadeningNatural broadening
determined by the lifetime of the excited statedetermined by the lifetime of the excited state
and Heisenberg’s uncertainty principleand Heisenberg’s uncertainty principle（10
-5
nm）
Doppler Broadening Doppler Broadening （10
-3
nm）
results from the rapid motion of atoms as they emit
or absorb radiation
Collisional BroadeningCollisional Broadening
collisions between atoms and molecules in the gas phase
lead to deactivation of the excited state and thus broadening
the spectral lines
Characters of the atomic absorption spectrum

18. Doppler Broadening Doppler Broadening （10
-3
nm）
results from the rapid motion of atoms as they emit
or absorb radiation
Characters of the atomic absorption spectrum

19. Application of AAS
Pretreatment (dissolution) is required for solid samples.
AASAAS

20. Polished rice:
0.118 ppm
Unpolished rice:
0.070 ppm
0.1 ppm
Furnace method
Injected amount: 10 µL
Interference inhibitor: Pd 50ppm 5 µL
Ashing: 400°C; Atomization: 1,800°C
Results of Quantitative
Analysis of Cd in Rice
Flame method
Air-C2H2
0.5 ppm
Polished rice :
0.118 ppm
Unpolished rice :
0.073 ppm
The following 2 methods can be used to analyze unpolished and polished rice decomposed using
acid:

21. AAS Interferences

22. AAS Advantages and
Disadvantages'
Advantages
1.High selectivity and sensitivity
2.Fast and simple working
3.Doesn’t need metals separation
Disadvantages
1.Analysis doesn’t simultaneous
2.Fragment have to form ready measure solution
3.Limit types of cathode lamp (expensives)

23. THANK YOU 

24. Questions
•How could atom’s collision
•Sample preparation of AAS
•The type of sample liquid or gas
•Function of AAS of few nonmetals
examples
•What happen to the sample in flame