This document discusses the principles and applications of atomic absorption spectrometry (AAS). It describes how AAS works by absorbing light of a specific wavelength to promote electrons in atoms to higher orbitals. It explains Beer's law that absorbance is directly proportional to concentration and path length. It also discusses instrumentation components like the light source, atomizer, detector, and applications like elemental analysis of metals in samples. The document concludes that AAS is useful for low-concentration metallic element analysis in solutions.
4. PRINCIPLE
The electrons of the atoms in the atomizer can be promoted to higher
orbital’s for a short amount of time by absorbing a set quantity of
energy (i.e. light of a given wavelength). This amount of energy (or
wavelength) is specific to a particular electron transition in a
particular element, and in general, each wavelength corresponds to
only one element. This gives the technique its elemental selectivity.
5. BEER’S LAW
The absorbance of that solution of concentration c is directly
proportional to path length through the solution and concentration
of absorbing species. That is A=abc,
a = proportionality constant called absorptivity
A=Absorbance of solution
When concentration is expressed in moles per litter and cell length is
in centimeter,the absorvity is called molar absorptivity (€).
A=€bc
b
• p₀ p
Concentration c
6. TRANSMITTANCE
The transmittance of the solution is the fraction of
the incident radiation transmitted by the solution .that is
T= P⁄P₀
Transmittance is often expressed in terms of percentage
ABSORBANCE
The absorbance of the solution is defined by the equation
A =
In contrast to transmittance the absorbance of a solution
increases as attenuation of the beam become larger.
7. A spectrometer comprises of following part
• Light source
• Atomizer
• Detection Instrumentation
• Amplifier
• Signal display
• Data station
17. APPLICATIONS
• The use of AAS instruments as detectors .
• Elemental Analysis.
1. Lead or cadmium in a drop of blood
2. Several metals in a needle tissue biopsy sample
3. Rubidium in an insect egg (solid sampling)
• Direct Solid-Sample AAS Analysis
• Air filter
18. • Determination of Alloying Elements in Steels by
Flame AAS.
Determination of Alloying Elements in Steels by
Flame AAS.
• Manganese, magnesium, chromium, copper, nickel, molybdenum,
vanadium, cobalt, titanium, tin, aluminum, and lead in iron-base alloys
can be readily determined using flame AAS.
• One-gram samples are first dissolved in 15 ml of a 2:1 hydrochloric/nitric
acid mixture. Then, 10 ml perchloric acid are added, and the solution is
heated to drive off most of the more volatile acids.
• After approximately 5 min of moderate heating following the first
appearance of perchloric acid fumes, the salts are dissolved, then diluted
to 100 ml with water.
• Elemental standards containing iron at the 1% concentration level are
prepared by adding suitable amounts of various 1000-ppm stock
solutions and water to a 5 wt% stock solution of high-purity iron
dissolved in the same manner as the samples.
• Iron at approximately the same concentration level in all of the solutions
exerts a leveling effect on nebulization/atomization.
19. ANALYSIS OF THERMITE BY FLAME
8Al + 3Fe3O4 9Fe + 4Al2O3 + heat
The amounts of Fe3O4 and aluminum in several unreacted thermite
samples were determined by measuring iron and aluminum in the
samples using flame AAS after dissolution in hydrochloric acid; the
amount of Al2O3 was calculated by weighing the insoluble residue.
• The samples (approximately 150 mg) were heated in 27 ml of
concentrated high-purity hydrochloric acid and 10 ml of water to dissolve
the Fe3O4 and aluminum.
• Each solution was filtered through a tared 1 A3 Berlin crucible. Solutions
were diluted so that aluminum concentrations ranged from 5 to 50 g/ml.
• To each, hydrochloric acid was added to obtain a final acid concentration
of 2 wt%. Iron and aluminum were determined from the same solution, to
which 0.1 wt% potassium (as potassium chloride) was added as an
ionization buffer for suppression of the ionization interference for
aluminum.
• The resulting dilutions were analyzed using an atomic absorption
spectrometer.
20. LIMITATION
• Detection limits range from subparts per billion
to parts per million
• Cannot analyze directly for noble gases,
halogens, sulfur, carbon, or nitrogen
• Poorer sensitivity for refractory oxide or carbide-
forming elements than plasma atomic emission
spectrometry
21. CONCLUSION
• Atomic absorption spectrometry is generally used for measuring relatively low
concentrations of approximately 70 metallic or semi metallic elements in solution
samples. The basic experimental equipment used is essentially the same as
that of 30 years ago--enhanced by modern electronics, background-correction
schemes, and alternate types of atomizers.
• The predominance of AAS in general-purpose trace-metal analysis has recently
been somewhat eclipsed by modern atomic emission spectrochemical methods
designed to permit solution analysis. However, its ruggedness and relatively low
equipment costs keep AAS competitive.
• Atomic absorption spectrometry performed using the graphite-tube furnace
atomizer usually remains the method of choice for ultra-trace-level analysis.
22. REFERANCE
• :
• ASM Handbook. Volume 10
• G. Kirchoff, Pogg. Ann., Vol 109, 1860, p 275
• G. Kirchoff and R. Bunsen, Philos. Mag., Vol 22, 1861, p 329
• T.T. Woodson, Rev. Sci. Instrum., Vol 10, 1939, p 308
• A. Walsh, Spectrochim. Acta, Vol 7, 1955, p 108
• W. Frech, E. Lundberg, and M. Barbooti, Anal. Chim. Acta, Vol 131,
1981, p 42
• 28. S. Backmann and R. Karlsson, Analyst, Vol 104, 1979, p 1017
• 29. F.J. Langmyhr, Analyst, Vol 104, 1979, p 993
• 30. J.J. Sotera and R.L. Stux, Atomic Absorption Methods Manual,
Vol 1, Standard Conditions for Flame Operation,
• Instrumentation Laboratory Report No. 42208-01, Sandia National
Laboratories, Albuquerque, June 1979
