Studies on the mechanisms of vaporization of analytes and matrices in electrothermal vaporization inductively coupled plasma mass spectrometry.

摘要

The mechanism of vaporization of platinum group elements (PGE's) in a graphite furnace was investigated using electrothermal vaporization inductively coupled plasma mass spectrometry (ETV-ICP-MS). The results indicated that Ru, Rh, Pd, Ir and Pt were reduced to the metallic state and vaporized by direct sublimation of the metal in the graphite furnace. For Os, two distinct vaporization processes were observed: volatile oxides of Os are released at low temperatures, but some of this oxide was reduced to relatively involatile Os metal, which was vaporized above 2000°C. The addition of a Te chemical modifier improved the analytical figures of merit for Os, but no effect on the other PGE's was observed.; Methods for minimizing isobaric interferences caused by carbon argides for the determination of chromium by ETV-ICP-MS were investigated. Methods compared included (a) use of alternative isotopes; (b) optimized temperature; (c) use of chemical modifiers. Under optimized conditions, it was possible to achieve improvement of the detection limit for Cr by a factor of 20. Addition of chemical modifiers such as NH₄ F and NaOCl caused increased background signals from carbon argides because of additional carbon removed from the surface of the ETV in the presence of these chemical modifiers.; Slurry sampling ETV-ICP-MS was used for the removal of silica for direct analysis of silica-rich solid geological samples. The effect of using HF as a chemical modifier to remove silica as the tetrafluoride was studied. It was found that HF was highly effective in removing silica if sufficient HF was added as a chemical modifier and an adequate reaction time allowed.; Effectiveness of ion-molecule reactions in a Dynamic Reaction Cell (DRC) in reducing or eliminating carbon-based polyatomic ions in ETV-ICP-MS was also studied. The use of a DRC permitted efficient removal of many carbon- and argon-based interferences and had the potential of eliminating other polyatomic interferences, such as, oxides. The results showed that the DRC was effective in reducing carbon-based polyatomic interferences in the determination of 52Cr, 53Cr, 24Mg, and 26Mg. For 28Si and 29Si the use of NH₃ gas was less effective. Interferences at m/z = 30 with 30Si + persisted and might require other gases or mixture of gases for the DRC to remove them.