1. Atomic absorption spectroscopy involves exciting the electrons in metal atoms to higher energy levels using light from a hollow cathode lamp emitting a characteristic wavelength for the metal of interest. 2. When the excited metal atoms return to a lower energy state, they emit electromagnetic radiation of a specific wavelength that is measured by a detector. 3. The amount of light absorbed is directly proportional to the concentration of metal atoms, allowing the technique to be used for both qualitative and quantitative analysis of metals in solutions.

3. Something you must know  – electrons are
found in increasing energy levels around the
nucleus.
#The electrons in the atom became excited i.e.
move to higher energy level (shell) when energy
is supplied
#The electron then return from an excited level
to a more stable energy level closer to the
nucleus.

4. #In making this transition between levels, the electron
released a FIXED quantity of energy (Quantum Energy) in
the form of electromagnetic radiation (light rays) of a fixed
wavelength.

5. The level of absorption of radiation
of a specific wavelength by a
sample is called its absorbance
*Absorbance is directly
proportional to the concentration

6. -The fraction of light of a given
wavelength absorbed will depend on
the concentration of the species in
solution.
-The higher the concentration, the
greater the amount of light absorbed
-This means that we can use the
absorbance of light for both qualitative
and quantitative analysis

8. • The corresponding spectrum may exhibit a continuum, or may have
superposed on the continuum bright lines (an emission spectrum) or dark
lines (an absorption spectrum), as illustrated in the following figure.

9. Origin of Continuum, Emission, and Absorption Spectra
• emission spectra are produced by thin gases in which the atoms do not
experience many collisions (because of the low density). The emission
lines correspond to photons of discrete energies that are emitted when
excited atomic states in the gas make transitions back to lower-lying
levels.
• A continuum spectrum results when the gas pressures are higher.
Generally, solids, liquids, or dense gases emit light at all wavelengths
when heated.
• An absorption spectrum occurs when light passes through a cold, dilute
gas and atoms in the gas absorb at characteristic frequencies; since the
re-emitted light is unlikely to be emitted in the same direction as the
absorbed photon, this gives rise to dark lines (absence of light) in the
spectrum.

13. Identifying an unknown compound
-The absorbance spectrum of a
particular compound is unique.
-A data bank of the absorbance spectra
for different compounds will allow the
analyst to identify an unknown
compound

16. Determining the concentration of a compound
in a mixture
-A series of standard solution is prepared
-The instrument is adjusted so that only light of
the wavelength of maximum absorbance is
passed through the test solution (sample) and
the standard solution (reference)

17. -By measuring the intensity of the light transmitted through
the sample, the instrument can provide a reading of its
absorbance

18. The readouts of absorbances for the standard
solution (reference) are use to produce a calibration
curve

19. • It identifies the element and determines the
concentration of the element in materials
•One of the most widely used of modern
instrumental technique
•Very versatile, being capable of detecting 68
elements

20. •Extremely sensitive, detecting concentrations of
element at parts per million (ppm) levels , in some
cases parts per billion (ppb)

21. •Used to determined the concentration of metal ions
in aqueous solution (for low concentration only,
accurate dilution is needed if the sample is too
concentrated)
•e.g. Drinking water, biological fluids (likes milk,
blood, urine), wine and effluent from industrial plant.
•If sample in solid form, it need to dissolve first.
•e.g alloys, hair, finger nails, foodstuffs, soil.

22. •If sample in gas form, it need to dissolve first also (pass the gaseous
sample through a solution that absorbs any constituents under
investigation) e.g cigarette smoke, exhaust gases from combustion of
fuels, air in indoor workplaces..

23. The practical requirements for atomic
absorption spectroscopy are as follows:
1.A source of radiation (Hollow Cathode
Lamp)
2.A system for placing the sample in the path
of the incident ray from the source
3.A monochromator which selects one
frequency of transmitted radiation to be
passed on to the detector
4.A detector to measure the intensity of the
transmitted radiation

24. Spectrophotometer

25. http://www.umd.umich.edu/casl/natsci/slc/slconline/ADVAA/AdvAA.swf

26. As a source to produce a sharp, intense and constant
light beam with specific wavelengths, i.e. to produce
electromagnetic radiation having energies characteristic
of the metal (characteristic/specific/unique excitation
wavelength)
* Exp. Magnesium hollow cathode lamp use to detect
magnesium only.
Schematic of a hollow-cathode lamp

27. -To vapourise or spray the sample (from
solution to gas) and mixed with the fuel-air
mixture
Flame mixture Exp:
air-acetylene (max temperature : 2250 C)
Nitrous oxide –acetylene (max temp :
2955°C)

28. - An “Atomic Cloud” is created, where
metallic compounds (in ion form) are
decomposed and the metal ions are
reduced to the elemental state by pick
up the free electrons in the flame.
Aspirator-burner + Flame == act as atomiser

29. To select one of the key absorption frequencies/
wavelengths for the metal under investigation.
In doing this, only a narrow spectral line impinges
on the detector.
Exp: Calcium- 422.7nm ; Iron- 248.3nm
The selected radiation is sent to a detector which
measures it intensity

30. 1. The atoms absorb unique wavelength of light to excite
their electrons to higher energy levels
2. Only atoms of the same element as the material in the
cathode of the hollow cathode lamp will absorb the
radiation, WHY??
3. atoms/metal ions require different energies and
therefore will absorb different wavelengths. There
would be no interference from other atoms/ions
present

31. 4. The amount of light being absorbed is
directly proportional to the number of the metal
atoms in the flame/i.e. the amount of light
absorbed measures the number of atoms
present (concentration)

32. -To do quantitative analysis by AAS, a calibration
curve must be obtained first
-Calibration data is obtained by measuring the
absorbance of a series of standard solutions of the
interested element
-A calibration curve can be obtained by plotting a
graph absorbance versus concentration
-The unknown concentration of the same element
can then be read from the curve by interpolation

33. AAS UV-Vis
deals with metallic atoms, it deal with molecules, it excites
excites valence electrons electrons in molecular orbitals
(i.e. electrons in bonds
, AAS operates in the visible operates over UV and visible
spectrum. part of the spectrum
a metal cathode lamp (matching uses a lamp that can generate a
the sample) wide spectrum
a monochromator to select one uses a monochromator
of these wavelengths to select the wavelength
required for the analysis
analyses vapourised metal analyses solutions
atoms

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