AAS DETECTION TECHNIQUE OF HEAVY METALS,

1. - BY
SUBHASISH DAS
M.PHARM 1ST YEAR
ROLL- 19320712001
REG. NO-121932310012 OF 2012-2013
CLASS ROLL – 13 .

2. INTRODUCTION
 Atomic absorption spectroscopy was introduced in mid 1950’s by
“Alan Walsh”.
 Most powerful technique to determine trace metals in liquid
quantitatively
 In a sentence “Atomic Absorption Spectroscopy (AAS) “ is a method
of elemental analysis , particularly useful for determination of trace
metals in liquid and is almost independent of the molecular form of
the metal in sample.

3. MERITS
 The atomic absorption technique is specific
because the atoms of a particular element can only
absorb radiation of their own characteristic
wavelength
 Some element possess higher detection limits by
atomic absorption like Ag , As , Au etc.
 Independent of flame temperature.

4. THEORY
 Atomic absorption spectroscopy deals with
absorption of specific wave length of radiation by
neutral atoms in the ground state.
 When a light of this wavelength is allowed to pass
through a flame having atoms of the metallic
species , part of the light will be proportional to the
density of the atoms in the flame.

5. EQUATIONS
 At ,
υ the total amount of light absorbed = ( e2/mc)*Nf
Where,
e = charge on electron.
m = mass of electron.
c = speed of light.
N = total number of atoms that can absorb frequency
ν in the light path.
f = the oscillator strength or ability for each atom to
absorb at frequency ν.
contd..

6. Contd..
As ,e, m, c are constant equation becomes
Total amount of light absorbed = constant * N * f

7. GROTRIAN DIAGRAMME
 Walter Robert Wilhelm Grotrian (21/4/1890 - 3/3/ 1954)
was a German astronomer and astrophysicist.
 Grotrian studied the emission line from the solar corona in
the green region of the spectrum; this emission line could not
be attributed to any known chemical element and was
thought to be a new element (which scientists named
"coronium").
 Grotrian and Bengt Edlén from Sweden demonstrated that the
two observed emission lines arise from iron atoms that have
lost about half their 26 electrons .

8. ATOMIC ABSORPTION TRANSITIONS

9. EFFECT OF FLAME
TEMPERATURE
e
g
g
=
N
N E
o
u
o
u ex
kT


•Effect of flame temperature: Since flame is at high temperature
might have an effect on fraction of atoms in excited state.
•Boltzmann's equation describes effect of flame temperature:
where

10. e
g
g
=
N
N
kT
E
o
u
o
u ex

Where,
Nu is the number of atoms in excited state
gu the number of degenerated orbitals on this energy level.
No and go refers to the same figures at ground state.
k is Boltzmann constant and
T is the temperature .
E is energy difference between two orbitals
Therefore, an increase in temperature results in an increase of the
number of excited atoms, which is equivalent to a lowering in
absorption

11. PRINCIPLE
Light source Light Light
DETECTOR
Gaseous
molecules
Solid/Gas
aerosol
Spray
S
I
G
N
A
L
RECORDER

12. A light beam is passed through the flame,
Radiation is absorbed, transforming the ground
state atoms to an exited state.

13. WORKING PRINCIPLE
 Liquid sample → formation of droplet → fine
residue
↓
neutral atom ← Formation of neutral atom
absorbs specific
Wavelength of radiation from hollow cathode lamp.
↓
Measurement of intensity of radiation absorbed by using
photometric detectors.

14. Atomic Absorption
Instrumentations

15. INSTRUMENTATION
SINGLE BEAM DOUBLE BEAM

16. MAJOR PARTS OF
INSTRUMENT
 HOLLOW CATHODE LAMP - The cathode is made up of specific element
or alloys of elements or coating of elements on cathode , as current is
applied between anode & cathode , metal atoms emerge from hollow cup
and collides with filler glass . Due to the collision, number of metal atoms are
excited and emit their characteristic radiation , this is absorbed by neutral
atoms of same element in ground state , occur in the flame , when sample
solution is sprayed. Band width-0.001to 0.01 nm.

17. CONTD…
 ATOMISER ASSEMBLY–
Assembly used as atomizer and nebulizer.
Premix type Total consumption Graphite furnace

18. INTERFERENCES
A. PHYSICAL – Due to sample matrix or flame or scattering or similar
alkali halides , termed as Background absorption.
remedy- use background corrector

19. CONTD..
B. CHEMICAL – In complete dissociation of
compound ,
remedy – 1. use high temperature flame
2. chemical means are applied.
C. IONISATION – Due to too high flame temperature.
remedy – addition of more easily ionisable
element.
D. SCATTERING EFFECTS – Due to presence of
high concentration of interfering element.
remedy – using a continuum source.

20. APPLICATIONS
 Estimation of trace elements in biological fluid.
 Estimation of Copper ,Zinc, Nickel in food products.
 Estimation of Zinc in Zinc insulin injection
 Estimation of lead in Calcium Carbonate, petrol.
 Estimation of elements in soil ,water, effluents,
ceramic etc.
ELEMENT Λ (nm) ppm
SODIUM 589 0.01
POTASSIUM 766.5 0.01
CALCIUM 442.7 0.05
LEAD 217 0.01

21. DETECTION LIMIT AND
SENSITIVITY
 The concentration of element present in the sample solution
which produces 1% absorption.
 Sensitivity , expressed in terms of μg/ml for 1% absorption.
 C1%=(C0.1*0.0044)/0.1
Where,
C1% = the concentration give rise to 1% absorption.
C0.1 = the concentration give rise to an absorbance of 0.1

22. DEMERITS
 A separate lamp for each element to be determined
is required.
 Elements produce oxides in flame may not be
successfully determined quantitatively.
 In aqueous solution , the predominant anions
affects the signal to a negotiable degree.

23. CONCLUSION
 ATOMIC ABSORPTION SPECTROSCOPY mainly
used to determine trace element in soil samples,
waters, petrol etc ; not just qualitatively, mainly
quantitative determination of metals are done .
 In case of isolation and purification of herbal drugs
or phytochemical form crude form AAS helps as a
support to determine the amount of trace material
present , so as an analytical tool it is very use full.

24. REFERENCES
1. G. R. Chatwal , S. K. Anand (2010) , Instrumental Methods Of
Chemical Analysis , Himalaya Publishing house , Ch – 13 , Pg. no. -
2.340 – 2.366 .
2 . A. H. Beckett , J. B. Stenlake , (2007) , Practical Pharmaceutical
Chemistry , CBS Publishers & Distributors Pvt. Ltd. , 4th ed. , part two,
Ch – 8 , Pg. no .- 346 – 357. CBS Pubs ISBN : 81-239-0514-9 ,
Athlone ISBN : 0-485-11323-8
3. Hobart H. Williard , Lynne L . Merritt, jr. , John A. Dean , Frank A.
Settle, jr. , Instrumental Methods Of Analysis , (2006), CBS Publishers
& Distributors Pvt. Ltd. , 7th ed. , Ch – 9 , Pg no – 243- 255 , ISBN :
81-239-0943-8