Simultaneous determination of platinum group elements and rhenium mass fractions in road dust samples using isotope dilution inductively coupled plasma-tandem mass spectrometry after cation exchange separation

Highlights: • Rapid method for PGE determination in samples with complex matrices. • Isotope dilution (ID) calibration strategy is used. • Offline matrix separation step is suggested before ICP-MS/MS measurement. • Use of NH₃ gas in on-mass measurement mode is preferred for all PGE analyses. Measurement of Platinum Group Element (PGE: Ru, Rh, Pd, Os, Ir, and Pt) and Rhenium (Re) in environmental samples is a difficult task due to their ultra-trace level concentrations, and these metals suffer from severe isobaric and polyatomic interference. These kinds of issues have been solved for environmental samples having simple matrices such as tunnel dust and moss. However, a scope of improvement still exists in challenging sample matrices such as road dust, soil, and rocks. In this study, a method that enables measurement of PGE and Re mass fractions in road dust and rock samples is proposed. The method involves matrix removal using a cation-exchange column followed by measurement using inductively coupled plasma tandem mass spectrometry (ICP-MS/MS, also known as ICP- QQQ-MS) with 10% NH₃ in He as reactive gas in Collision/Reaction Cell. This study emphasizes that the usage of a simple cation-exchange column is an important step over the framework developed by Suoranta et al., 2012, which was developed to measure PGE and Re fractions in environmental samples having a simpler matrix such as moss samples. The method combines high pressure (130 bars) and high temperature (220 °C) digestion procedure in combination with isotope dilution (ID) as a calibration strategy, PGE and Re separation using cation exchange resin, and their measurements using ICP-MS/MS. The method was validated with road dust (BCR-723) and ultramafic komatiite (OKUM) having a complex matrix. The measured PGE and Re mass fractions of the two-measured reference material show excellent agreement with their certified values and have intermediate precisions ranging from 0.4–7.7% RSD. We conclude that the combination of single-stage cation-exchange chromatography with ID-ICP-MS/MS measurements enables measurement results with uncertainties fit for purpose for PGE and Re mass fractions in environmental samples with a complex matrix.