Atomic Absorption Spectrometry (AAS):

In this technique, the atomic vapours holding free atoms of an element within the ground state are subjected to a UV-VIS radiation source emitting a features frequency of the element present in atomic vapours. A radiation is absorbed and the intensity of the radiation is attenuated. An absorbed radiation causes excitation of electrons from the ground state to an excited stage. The extent of absorption is a quantitative measure of the concentration of atomic vapours of the element within the ground state. That is an electronic excitation and the energy of transitions lies within the to UV-VIS region of the electromagnetic spectrum.