Principle of Atomic Absorption Spectrophotometry:

The concept of atomic absorption spectrometry (AAS) was proposed through two groups within the year of 1955, A. Walsh of Australia and another one of C T J Alkamade and J M W Milatz from The Netherlands. You have learnt which in atomic spectroscopy; the analyte must be present within the atomic vapour state. Within atomic absorption spectrophotometry the atomisation is performed through aspirating the sample solution within a flame whereas the analyte element is converted within gaseous phase atoms. Instead, the sample is fed within a graphite furnace whereas the atomisation is achieved electrothermally at associative lower temperature that was below 3000 K. As the temperature of atomisation is low; most of the atoms remain within the ground state that could absorb features radiation from the radiation source made from the analyte element. An atomic vapour containing free atoms of an element in the ground state is illuminated by a radiation source emitting the features radiation of the analyte. In halogen cathode lamp the cathode is made of the element which requires being determined and provides radiations features of the element.

The radiation is absorbed through the analyte vapours and its intensity decreases. This is same to spectrophotometry that you have learnt earlier; molecules being replaced through atoms and the lamp modified to a line source. The degree of absorption is a quantitative measure of the concentration of ground state atoms within the vapours. The analysis is completed through comparing the observed absorption along with the one acquired through suitable a standard sample of the analyte under same experimental conditions, that is a calibration curve method is commonly employed.