A method for determination of PGE–Re concentrations and Os isotopic compositions in environmental materials

Abstract

Automobile catalyst emissions not only result in increasing environmental concentrations of Pt, Pd, and Rh, but also Os, Ir, and Ru. Little is known about the behavior of platinum-group elements (PGE) and Re in the environment and their potential risk to humans and, as such, the monitoring of Os, Ir, Ru, and Re concentrations in environmental samples is necessary. We present an improved procedure for determination of PGE–Re concentrations and ¹⁸⁷Os/¹⁸⁸Os ratios of the environmental reference material BCR-723 by isotope dilution inductively coupled plasma mass spectrometry (ID-ICP-MS) and negative thermal ionization mass spectrometry (N-TIMS), respectively. The sample is digested with inverse aqua regia in a Carius tube. After Os separation by CCl₄ solvent extraction, separation and purification of PGE and Re from sample matrix elements is sequentially performed by a two-stage tandem column setup using cation exchange and N-benzoyl-N-phenylhydroxylamine (BPHA) extraction resin. Elution of 0.1 mol L⁻¹ HCl efficiently removes interfering elements such as Zr, Hf, Mo, and Cd in the final purified sample prior to ID-ICP-MS determination of PGE and Re. Analyses of BCR-723 yield reproducible results and well-defined average Pt, Pd, Os, Ir, Ru, and Re concentrations of 79.8 ± 6.0, 4.6 ± 0.8, 0.37 ± 0.04, 0.23 ± 0.12, 1.1 ± 0.3, and 6.5 ± 0.1 ng g⁻¹, respectively (95% confidence level; n = 10). The ¹⁸⁷Os/¹⁸⁸Os ratio of this standard was determined to be 0.537 ± 0.022 (95% confidence level; n = 10). These are the first comprehensive PGE and Re concentrations and Os isotopic compositions reported for BCR-723 and provide a well-characterized standard for assessing the data quality of autocatalyst PGE measurements and related research on environmental materials. The method was successfully employed in the determination of PGE and Re concentrations and Os isotopic compositions in urban road dust samples.