Revisiting the sodium and calcium matrix effects in inductively coupled plasma optical emission spectrometry. Excitation mechanisms by inelastic collisions

Abstract

The dependence of calcium and sodium matrix effects on the total excitation energy of analyte emission signals was used as a tool for the study of excitation mechanisms in radial view mode inductively coupled plasma optical emission spectroscopy. A total of 95 atomic and 66 ionic emission signals of aluminum, cobalt, chromium, iron, magnesium, manganese, nickel, and silicon in the 3.0–17.59 eV energy range were measured at the non-robust plasma operating conditions to facilitate the matrix effect study. Different matrix effects versus total excitation energy relationships were observed regarding the energy interval. The change of sign from negative to positive of the both matrix effect versus total excitation energy relationship observed around 14 eV, in the 12.06–17.59 eV energy range, is interpreted as experimental evidence of the action of two non-thermic excitation mechanisms: Penning ionization from approximately 12 to 14 eV and charge transfer from 14 to 17 eV. Based on the energy resonance principle and total spin conservation Wigner’s Theorem, possible reactions between excited ionic argon and ground state analyte ions were proposed.