Solubility of emitted platinum group elements (Pt, Pd and Rh) in airborne particulate matter (PM10) in the presence of organic complexing agents

Abstract

The purpose of this study was to examine the influence of the common organic complexing agents, L-methionine and ethylenediaminetetraacetic acid (EDTA), on the solubility of the platinum group elements (PGE), platinum (Pt), palladium (Pd) and rhodium (Rh), associated with field-collected airborne PM10. For comparative purposes, the Standard Reference Material 2557 (Used Auto Catalyst Monolith) was also analysed. The concentrations of PGE were determined for both soluble extracts and the filtered insoluble elemental fractions. To minimize matrix effects, samples first underwent a co-precipitation procedure with Te prior to the determination of Pt and Rh. Platinum concentrations were measured using isotope dilution ICP-Q-MS in collision mode with He, while Rh was determined via ICP-Q-MS. For Pd, samples were first co-precipitated with Hg, before concentrations were determined using isotope dilution ICP-Q-MS, also in collision mode with He. The results demonstrate that the presence of the L-methionine, and EDTA increase the solubility of Pt, Pd and Rh present in airborne PM and the SRM 2557. Samples extracted with solutions containing L-methionine had relatively large soluble fractions of 39 % for Pt, 27 % for Pd and 26 % for Rh. Similarly, Pt, Pd and Rh extracted with a solution containing EDTA had an average solubility of 33, 45 and 35 % for these three elements, respectively. The solubility of PGE present in the catalytic converter material was much lower, with <4 % for Pt, Pd and Rh. This demonstrates that PGE species present in airborne PM are more soluble compared to that in automotive catalytic converters.