Studies on the Ion Formation in Glow Discharge Mass Spectrometry Ion Sources

For a better understanding of the ion formation in a glow-discharge mass spectrometer, the values of ion beam ratio (IBR) of various ion species to singly charged ion M+ or Ar+ were compared for the both pin samples and disk samples of thirty-nine high-purity metals. The doubly charged ions such as Pr2+, Nd2+ and Sr2+ and the dimer ions such as Al2+, Ag2+ and Zn2+ showed higher IBR values beyond several %. The IBR-values of doubly charged ions showed a tendency to decrease with the values of the 2nd ionization potential and a particularly good linearity between them was found for rare earth metals. The IBR-values of argide ions (MAr+) showed the tendency to increase with the values of the 1st ionization potential, although such a relation was not found for dimer ions (M2+). These results were suggested by the analysis of reaction formulas. The difference basing on the discharge cell structure was found for the formation of M2+ and MAr+; the IBR-values of M2+ of disk samples were smaller than those of pin samples by 1-3 orders of magnitude and those of MAr+ of disk samples were one order of magnitude larger. The ratio of the yields of Ar+, Ar2+ and Ar2+ was about 100 : 10 : 1, which agreed with the ratios found in previous works. The amounts of Ar4+ and Ar5+ were below the detection limit. Between the doubly (Ar2+) and multiple charged (Arn+ : n≥3) ions, a larger drop of the IBR-value than expected form the linearity to ionization energy was found.