QUANTITATIVE-ANALYSIS IN SPARK SOURCE-MASS SPECTROMETRY

The ionization mechanism in the rf vacuum spark is considered. It is shown that anode and cathode plasma can be studied by means of liquid metal ion sources in the cathode or anode mode. Equilibrium isothermal plasma with kT = 6 eV and ne = 1019 cm-3 was found to occur upon explosion of cathode microprotrusions. On expansion into a vacuum isothermal plasma transforms into nonisothermal plasma in which the ion temperature is proportional to the charge. The main parameters of nonisothermal anode plasma have been determined: particle concentration 1016 cm-3, temperature of singly-charged ions kT = 0.6 eV. It was found that the ions pulled out from the spark interelectrode gap are formed in explosive emission cathode plasma, and the ions originating in anode plasma are not involved in the formation of the mass spectrum. Based on these investigations, analytical expressions for calculating the impurity-matrix ionization ratio are suggested. The use of ionization ratios allows the accuracy of impurity analysis in spark source mass spectrometry to be improved. © 1990.