Determination of Ru and Os with enhanced sensitivity and Rh, Pd, Pt and Ir at sub ng g−1 levels in geological samples by ICP-MS

Abstract

The precise and accurate determination of platinum group elements (PGEs) at low abundance levels remains challenging. Here, an improved method was developed for the determination of ruthenium (Ru) and osmium (Os) with high sensitivity, as well as other platinum group elements (Ir, Rh, Pt and Pd) in geological samples, by isotope dilution-inductively coupled plasma-mass spectrometry (ID-ICP-MS). Following the decomposition of the samples with NaOH–Na₂O₂ fusion and subsequent acidification with HNO₃, Ru and Os were distilled in the form of volatile RuO₄ and OsO₄, respectively, using an oxidant, K₂S₂O₈. The RuO₄ and OsO₄ were simultaneously absorbed with H₂O with yields of 84.3 and 92.9%, respectively, resulting in a higher sensitivity of 60-fold for Ru and 11-fold for Os relative to their low valences by ICP-MS analysis. After distillation, HF was added to the remaining sample to remove silica, and dissolved in 3 mol l⁻¹ HCl. Then Pd, Rh, Ir and Pt were co-precipitated with tellurium (Te), dissolved in 0.24 mol l⁻¹ HCl, and analyzed directly by ICP-MS. The entire procedural blank of this method was evaluated and found to range from 11 pg for Rh to 300 pg for Pd. The proposed method was validated with nine geological reference materials, including GBW07289 (GPt-2), TDB-1, and WGB-1, with very low PGE contents. Given the sample heterogeneity and digestion efficiency of different methods, our results are comparable to those previously reported. The newly developed method can be applied to the PGE analysis of low-abundance samples (e.g., basaltic rocks and sediments).