Determination of Pt, Pd and Rh by inductively coupled plasma sector field mass spectrometry (ICP-SFMS) in size-classified urban aerosol samples

Abstract

Pt, Pd and Rh concentration levels related to particle size distribution were measured in Viennese aerosol. The urban aerosol was studied over a period of 1 month during summer 2002 in a heavy traffic area. A 6-stage cascade impactor collected classified particles with aerodynamic equivalent diameter (aed) <10 µm. Total suspended particulate matter (aed <30 µm) was assessed by filtering air (open face sampling head). The analysis of Pt, Pd and Rh in aerosol samples required a different strategy for each element to obtain accurate results and maximum sensitivity. Sample preparation was carried out by microwave-assisted acid digestion. For the determination of Pd an anion-exchange procedure was implemented. The digested samples were measured by ICP-SFMS in combination with ultrasonic nebulization and membrane desolvation, utilizing the high-resolution capabilities of this instrument for the determination of Rh. Pt and Pd were quantified by isotope dilution (IDMS), Rh by external calibration. Excellent detection limits of 0.07, 0.06 and 0.05 pg m⁻³ (impactor substrates) and 0.18, 0.22, 0.14 pg m⁻³ (open face sampling head substrates) for Pd, Pt and Rh, respectively, could be achieved. Since platinum group elements (PGE) are emitted from car catalysts as a result of mechanical processes, Pt, Pd and Rh were mainly found in the coarse fraction of urban aerosol. Summing up the concentrations assessed for the impactor stages (aed <10 µm) revealed a weekly average of 4.3 ± 1.7, 2.6 ± 0.6 and 0.4 ± 0.1 pg m⁻³ for Pt, Pd and Rh respectively. Concentration levels of samples collected with the open face sampling head (aed <30 µm) over the period of one week were significantly higher with average values of 38.1 ± 6.3, 14.4 ± 3.1 and 6.6 ± 2.4 pg m⁻³. Moreover, the presence of a collective of small particles containing the three investigated PGE was shown. Investigation of the impactor samples revealed an analogue size distribution for Pt, Rh and Pd with a maximum at 1–2.15 µm aed. These particles are toxicological relevant, as they penetrate deeply in human lungs (particles of 0.1–2.5 µm aed are deposited in the lung alveoli).