Sensitivity amplication by sample preconcentration in ion beam analysis

The development of ion beam techniques, namely particle induced X-ray emission (PIXE) and charged particle activation analysis (CPAA), for the determination of the platinum group elements (PGEs) in terrestrial rocks is described. The noble metals are heterogeneously distributed in rocks and ores which necessitates that large sample sizes be analysed to obtain representative results. A nickel sulphide fire-assay technique has been utilized to concentrate the noble metals from a large sample (50 g). The concentrated noble metals are finally retained on a filter membrane that is used as the target for ion beam analyses. Limits of determination of 0.5 ng/g were established for ruthenium, rhodium and palladium and 1 ng/g for platinum by PIXE; whereas osmium could be determined at 0.5 ng/g levels by CPAA. The ion beam techniques compare most favourably in terms of rapidity, expense and sensitivities for the platinum group elements, with other analytical techniques.