Classical and New Procedures of Whole Rock Dissolution for Trace Element Determination by ICP-MS

Sample digestion is a critical stage in the process of chemical analysis of geological materials by ICP-MS. We present a new HF/HNO3 procedure to dissolve silicate rock samples using a high pressure asher system. The formation of insoluble AlF3 was the major obstacle in achieving full recoveries. This was overcome by setting an appropriate digestion temperature and adding Mg to the samples before digestion. Sodium peroxide sintering was also investigated and the inclusion of a heating step to the alkaline sinter solution improved the recoveries of thirteen elements other than the lanthanides. The results of these procedures were compared with data sets generated by common acid decomposition techniques. Forty-one trace elements were determined using an ICP-QMS equipped with a collision cell. Under optimum conditions of gas flow and kinetic energy discrimination, polyatomic interferences were eliminated or attenuated. The measurement bias obtained for eight reference materials (BCR-2, BHVO-2, BIR-1, BRP-1, OU-6, GSP-2, GSR-1 and RGM-1) and intermediate precision (RSD) were generally better than +/- 5%. The expanded measurement uncertainties estimated for two certified reference materials were mostly between 7 and 15%. New data sets for the reference materials are provided, including constituents with previously unavailable values and also for the USGS candidate reference material G-3.