Laser ablation-inductively coupled plasma-mass spectrometry using a double-focusing sector field mass spectrometer of Mattauch–Herzog geometry and an array detector for the determination of platinum group metals and gold in NiS buttons obtained by fire assay of platiniferous ores

Abstract

This paper explores the potential of laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) for the determination of Au, Ir, Pd, Pt, Rh and Ru in NiS buttons obtained by fire assay of platiniferous ores using a new type of ICP-MS instrument equipped with an array detector Mattauch–Herzog spectrometer. The method evaluated comprises the NiS fire assay of a representative amount of the ore sample (40–75 g), grinding of the NiS buttons subsequently obtained, pelleting of the resulting powders using polyethylene wax as a binder, and LA-ICP-MS analysis of the sample using in-house matrix-matched standards for calibration. The use of this new ICP-MS device proved very beneficial in this context, offering a remarkable level of precision (2–3% RSD for the most abundant analytes, Pt, Pd, Rh and Ru, and 6–11% RSD for Au and Ir) owing to its simultaneous capabilities and its extended linear range, which enabled an improved performance of the internal standard (61Ni). Moreover, the low level of argide-based interferences and the detection power of the instrument provided low limits of detection (10 ng g−1 level) even for those elements that could be potentially affected by ArNi+ and ArCu+ overlap in this particular matrix (Pd, Rh, Ru). The accuracy finally obtained (90% of results within 10% of the reference value, and 70% of results within 5%) is fit-for-purpose for this application. The resulting method can be thus considered very attractive as a faster and greener strategy for the control of these types of samples in the platinum group metal industry, circumventing the need for the cumbersome and environmentally unfriendly digestion procedures currently employed.