Abstract: Three parameters have been introduced to modify the Saha ionization equilibrium in a spectrochemical ICP.These parameters provide the necessary modifications for the temperature difference between heavier particles and electrons, for the emission from an opticalthin ICP, and for the ambipolar diffusion of ion-electron pairs, respectively.It is confirmed that the overpopulation of electron number density in the central channel of ICPis mainly caused by the ambipolar diffusion process.As a consequence, this process enhances the charge exchange process between argon ions and analyte atoms in the central channel,which is principally responsible for the overpopulated analyte ion number density.

Key words: ICP-AES, Non-Saha ionization equilibrium, Ambipolar diffusion