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Determination of platinum group elements (PGE) in environmental samples by ICP-MS: a critical assessment of matrix separation for the mitigation of interferences

¹ Kasa Environmental, PO Box 239, Innaloo, WA 6918, Australia Corresponding author: (e-mail: jaywhiteley@kasaenvironmental.com.au)
² School of Environmental Science, Murdoch University, Perth, Western Australia, 6150, Australia

The accurate determination of Pt, Pd and Rh (platinum group elements, PGE) in environmental samples by inductively coupled plasma–mass spectrometry (ICP-MS) is complicated by molecular ion and doubly charged ion interferences (e.g. CuAr+, HfO+, SrO+, YO+ and Pb2+). Two matrix separation techniques, tellurium coprecipitation and ion exchange, are compared in terms of PGE recovery and separation efficiency by application to standard solutions and the new reference material BCR-723, a road dust material collected from the Tanzenberg Tunnel in Austria. Ion exchange using Dowex AG50W-X8 strong cation exchange resin is highly effective in terms of both separation efficiency (>99.7%) and PGE recovery (93.8 to 101.6%) and allows accurate, interference-free determination of PGEs. PGE recoveries by Te coprecipitation are incomplete, ranging between 84 and 93%. Significant amounts of copper (up to c. 30%) are also recovered, which, due to CuAr⁺ formation, causes interferences on both ¹⁰³Rh (monoisotopic) and ¹⁰⁵Pd. The generally high levels of interferent elements in environmental matrices (e.g. Cu, Pb etc.) and the magnitude of Cu recovery by Te coprecipitation limit the applicability of data correction using interference equations. Reductions in Cu yield by Te coprecipitation, to <4%, can be achieved through the addition of potassium iodide prior to matrix separation. However, due to the incomplete recovery of PGEs, ion exchange provides a more robust method for the determination of low levels of PGEs.

KEYWORDS: environmental samples, platinum group elements (PGE), matrix separation, inductively coupled plasma–mass spectrometry, tellurium coprecipitation, ion exchange