Abstract

Noble metals are subject to a number of significant oxide-based interferences in ICP-MS analysis. Quantification of these interferences has been largely overlooked despite evidence which suggests that they may, in some cases, represent a significant source of analytical error. Their removal would therefore constitute a significant improvement in analytical accuracy. In this study the oxides that interfere with noble metal analysis have been quantified relative to CeO⁺/Ce⁺ ratios. A dynamic reaction cell (DRC) based solution to the problem is introduced, which works in complete contrast to conventional ICP-MS analysis where the formation of oxides is undesirable and operating conditions are optimised to limit their production. Oxygen reaction gas is utilised actively to promote oxidation of interfering species to higher oxides, with a resulting separation of analyte from interfering oxide. Results are presented for Hf, Ta, Nb, and Zr where the single oxide interferes with a noble metal analyte mass. Various higher oxides are formed, leaving the mass free from interference. The reaction mechanism has been determined in each case by monitoring of new multiple-oxide species and scans of the entire mass range to identify new product species. Results confirm the success of an in-cell separation of analyte from metal oxide, facilitating improved detection limits and isotope-ratio precision. The suitability of this method for general environmental use is demonstrated by analysis of a certified soil reference material and isotope-ratio analyses.