A comparison of the capacity of FA-ICP-MS and FA-INAA

The platinum-group elements (PGEs) are commonly determined by INAA and ICP-MS after a NiS fire assay preconcentration. The results of the initial round robin for the PGEs and gold were examined for geological Canadian reference materials (WGB-1, TDB-1, UMT-1, WPR-1, WMG-1, and WMS-1). The Au accuracy is generally within 15% for both methods. For Ir, Os, Pd, Pt and Rh the accuracy for most samples is better than 10% for FA-ICP-MS and FA-INAA (true only for sulfide-bearing samples in the case of FA-INAA). Ru is not very accurate by either methods. Ru and Au have problems with precision which is interpreted to be related to the loss of gold in the dissolution step and for Ru, the source of the problem is not yet understood. Kurtosis show that FA-INAA has higher clustering than FA-ICP-MS for most analytes. It suggests a slightly better precision for FA-INAA. This is explained by the robustness of INAA after the NiS preconcentration despite its lower instrumental precision versus the complex dissolution steps involved in ICP-MS. For samples richer in PGEs (sulfide- and/or oxide-bearing rocks) both methods perform adequately but for low PGEs concentration samples (crustal rocks) ICP-MS shows an advantage.