Direct current glow discharge mass spectrometric analysis of non-conducting materials using a surface coating method

Abstract

A surface coating method was developed to analyze some non-conducting materials using the pin cell of a direct current glow discharge mass spectrometer (dc-GD-MS). As the materials were non-conducting there were many problems associated with sustaining a dc glow discharge, and this could be overcome by coating the surface with a very thin layer of conducting material. During the sample preparation process the melted indium was coated manually onto the surface of the sample, thus supporting the sputter process and causing the sample to be sputtered and ionized for analysis. After optimization of the plasma conditions, the prepared samples could be analyzed directly by dc-GD-MS with satisfactory detection limits, stability and reproducibility. Two NIST standard reference materials were used to validate the precision, accuracy and reproducibility of this method. The results showed that this method could avoid grinding, sustain the relatively stable discharge and enhance the stability of signals compared to the method of using a cathode made from indium pin rolled in the sample powder.