Download Origin of an Atomic Absorption Peak

Origin of an Atomic Absorption Peak
Energy Transition
E2
DE = hn
E1
Absorption Spectrum
Intensity
n
Frequency
1
Atomic Absorption for a Hydrogen Atom
Electronic energy levels
in a H atom
1s 2s 2p 3s 3p 3d
The lowest energy state
has the single electron in
the 1s orbital
1s1
2
A brief history of
Atomic Absorption Spectrometry
• 1802 Wollastone - discovered black lines in Sun's
spectrum which were subsequently investigated by
Fraunhoffer (1823).
Solar spectrum
3
A brief history of
Atomic Absorption Spectrometry
– 1820 Brewster - suggested black lines in solar
spectrum due to absorption processes in Sun's
atmosphere.
– 1859 Kirchhoff and Bunsen - demonstrated Na D line
absorption in visible spectra.
4
A brief history of AAS
Interpretation of Fraunhoffer lines in terms of atomic
absorption by elements in the suns atmosphere
1859-1955 Astronomers use atomic absorption to
estimate metal concentrations in atmospheres of stars.
Solar spectrum
Hydrogen spectrum
5
Mercury spectrum
What is AAS?
(AAS) Atomic Absorption Spectroscopy is:
• Quantitative technique
• Typical samples: low viscosity samples
• Generally uses to determine the amount of several
metals (e.g. Cu, Fe, Zn, Mg) in the soil, blood, air,
water, and food.
• Occasionally can be use as a qualitative technique
(can indentify chemicals that are present) – 68
elements
• In the electromagnetic spectrum, it uses
the visible part to detect the presence of
metals.
• Foundation of the technique: the
absorption of the light energy that has
the right wavelength causes the electrons
from the sample to be promoted from a
lower energy level to a higher energy
level.