Determination of Pt, Pd, Ru and Ir in geological samples by ID-ICP-MS using sodium peroxide fusion and Te co-precipitation

Abstract

A method is proposed for the determination of Pt, Pd, Ru and Ir in geological samples by isotope dilution-inductively coupled plasma mass spectrometry (ICP-MS). Mono-isotopic elements Rh and Au are determined by external calibration using Lu as the internal standard. Sodium peroxide fusion in corundum crucibles (instead of glassy carbon or zirconium crucibles) is used to decompose the samples. After dissolution of the fused cake in water, the solution is spiked with enriched stable isotopes of Pt, Pd, Ru and Ir, and then acidified with HCl. This solution is then evaporated to dryness promoting the formation of anhydrous silicate from colloidal material. PGEs and Au are then pre-concentrated by Te co-precipitation. The reagents HCl and SnCl2 are purified by Te co-precipitation. PGE blank levels are thus only derived from the Na2O2 which has PGE concentrations of <0.02 ng/g. Lutetium is added as the internal standard to correct for instrument drift and matrix suppression effects for the determination of the mono-isotopic elements. Method detection limits range from 0.02 to 0.3 ng/g. The results obtained for the CCRMP (CANMET, Ottawa, Canada) certified reference materials WGB-1 (gabbro), TDB-1 (diabase), UMT-1 (ultramafic ore tailings), WPR-1 (altered peridotite), WMG-1 (mineralized gabbro), and WMS-1 (massive sulphide) are in good agreement with certified values.