Comparative study of the excitation/ionization capacity of direct current versus radiofrequency powered glow discharge optical spectrometry

Abstract

A comparison of the excitation ability of radiofrequency (rf) and direct current (dc) powering modes in glow discharge (GD) optical emission spectrometry, using the same discharge chamber based on the Marcus design, is presented. Three cathodes of pure Sn, Zn and Cu were used to investigate the behaviour of atomic and ionic emission lines of these analytes and the discharge gas (argon) under different operating conditions in the 200-500 nm region. At a given pressure it was observed that atomic line intensity ratios between rf- and dc-GD for Ar I emission lines were higher the higher the upper level energy of the transition, whereas such ratios were independent of the energy of the upper level for Ar II lines. Considering the excitation of analyte emission lines, at selected operating conditions of the discharges, it was observed that lower intensities with the rf powering were due to lower sputtering rates because the emission yields were higher for the rf mode. The effect of pressure was also studied and it was found that the behaviour followed by both the atomic and ionic emission lines of argon, as well as the analytical line intensities, was not apparently related to the energy of the upper level of the transitions.