When the homogeneous solution of a representative sample is sprayed onto a flame (Air-Acetylene or Acetylene-Nitrous oxide), free atoms formed in the flame absorb characteristic radiation of the same element emitted by a hollow cathode lamp and undergo transitions to excited energy levels. This energy absorption by free atoms of the sample formed in the flame is proportional to the concentration of atoms formed in the flame and is governed by Lambert-Beer Law.

Samples can be in both solid (homogenized powders) and liquid form. For powder samples, the minimum quantity of sample required for analysis is 1 gm. For liquid samples, the solvent used must be specified.