Determination of platinum, palladium, iridium and gold in selected geological reference materials by radiochemical neutron activation analysis: comparison of procedures based on aqua regia leaching and sodium peroxide sintering

Abstract

A rapid and sensitive neutron activation method for the determination of platinum, palladium, iridium and gold in rocks is described. The procedure consists of thermal neutron irradiation of about 250 mg of sample, followed by chemical treatment of the rock, precipitation of gold and the platinum group elements with tellurium and high-resolution gamma-ray spectrometry with a hyper-pure Ge detector. Two different methods were used for the chemical treatment of the rock: aqua regia leaching and sintering with sodium peroxide. The procedures were evaluated by analysis of the certified reference material SARM-7 and the reference material CHR-Pt+. Sintering with sodium peroxide and precipitation with tellurium were more appropriate for the determination of Pd, Pt and Ir, giving results in good agreement (within ±10%) with literature values. For gold, aqua regia leaching gave more accurate results (relative errors from 0 to 6%). The detection limits for the analytical conditions employed were 0.1 µg kg^–1 Au, 10 µg kg^–1 Pd, 20 µg kg^–1 Pt and 0.2 µg kg^–1 Ir. The procedure employing fusion with sodium peroxide was applied to the analysis of the reference material CHR-Bkg and the concentrations of Au, Pt, Pd and Ir obtained are presented.