Spectroanalytical methods which involve interaction of electromagnetic radiations with matter have become the most important tool of analytical chemistry today.

Electromagnetic radiations are a form of energy that is transmitted through space at an enormous velocity. These rays do not require any supporting medium, such as air, instead they pass more readily through vacuum. These radiations are usually described in terms of wave-length (λ), wave number (v) and frequenty (v). Wave length is the distance between the two successive peaks of a wave, wave number is the number of waves per centimetre and frequency is the number of waves per second. Following relationship exists between the three quantities:

(Where c is velocity of electromagnetic radiations in vacuum = 3 x 1018 cms per second)

The most important consequence of interaction between electromagnetic radiations and matter is that energy is either absorbed or emitted by the matter in discrete amounts known as a photon or quanta. The energy of a quantum is given by the expression:


E = hv

Where E is energy in ergs and h is a constant known as Planck’s constant and has a value of 6.624 x 10-27 ergs-sec. Energy content of electromagnetic radiations rises with increase in frequency c as h is constant. As frequency equals to – the above expression becomes A which means that with rise in wave length the energy content of waves diminishes.