Origin of an Atomic Absorption Peak

E2

E1

DE = hn

Frequency

Intensity

n

Energy Transition

Absorption Spectrum

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

Hydrogen spectrum

Solar spectrum

Mercury spectrum

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.

5

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.