Characterization and optimization of a radiofrequency glow discharge ion source for a high resolution mass spectrometer

Abstract

A radiofrequency (rf) powered glow discharge ion source has been designed and coupled to a double-focusing mass spectrometer. An electrical interface has been developed to provide an effective rf power transfer, thereby ensuring rf shielding and grounding, and to couple the ion source to the accelerating potential. The device permits the direct analysis of almost any solid sample type (conducting, semiconducting and non-conducting). In order to establish optimum conditions for the trace analysis of solids, mass spectrometric studies of the dependence of ion signal intensities in an rf glow discharge on operating parameters (applied rf power and discharge gas pressure) were carried out. The energy distribution of the ion species was measured by the accelerating voltage scan. It was shown that the singly charged atomic ions of the sample have about a 10 eV higher average energy than the discharge and residual gas ions. An effective energy separation of the analyte ions from the discharge and residual gas ions was achieved by setting the position and width of the energy window of the double-focusing mass spectrometer. The optimization of the operating parameters of a glow discharge ion source and correct adjustment of the ion transfer optics of a mass analyser permit an improvement in the analytical characteristics of the elaborated device.