Investigation of charge transfer with non-argon gaseous species in mixed-gas inductively coupled plasma–atomic emission spectrometry

Potential charge-transfer reactions with non-argon gaseous species in a mixed-gas inductively coupled plasma were probed by means of two different experimental methodologies, namely the plasma-related matrix-effect approach and the relative-intensity technique. The foreign gases, introduced one by one into the central channel, were oxygen, hydrogen, nitrogen, krypton, methane and carbon dioxide at volumetric concentrations of 15%, 10%, 5%, 100%, 3% and 3%, respectively. Both matrix effects and relative intensities showed no change in behavior for emission lines with excitation energies in the vicinity of the ionization potentials of the foreign gases. This pattern suggests that the contribution of charge transfer from the foreign-gas ion is not important to the overall ionization and excitation of the analyte, in the normal analytical zone of the plasma and at the concentration of foreign gases used here.