Influence of propane on the atomic emission and atomic absorption signals in an inductively coupled argon plasma

Abstract

The introduction of 20 cm³ min^–1 of propane into a 1 kW argon pencil plasma was found to promote the reduction of refractory metal oxides into free metal atoms but at the same time to cause a reduction in the energy of the plasma. The extent of the reduction reaction for a range of different elements was monitored by conducting sequential atomic absorption spectrometric (AAS) and atomic emission spectrometric (AES) measurements in the pencil plasma. Ground-state populations were monitored through AAS measurements whereas the excited-state populations were monitored with AES measurements. The magnitude of the increase in the AAS signal was found to be related to the dissociation energy of the metal oxide. Elements that form stable refractory compounds were found to exhibit a greater enhancement than non-refractory elements in AAS. The controlling factor in the AES signal behaviour is the transition energy of the excited-state analyte species. Because a reduction in plasma energy of 150 W occurs when propane is added to the discharge, analytes possessing the larger transition energies are more affected. Therefore, mild refractory elements that possess larger transition energies, such as calcium, are capable of exhibiting a depression of the AES signal while simultaneously displaying an enhancement of the AAS signal in the pencil plasma.