Analytical problems in the determination of platinum-group metals in urine by quadrupole and magnetic sector field inductively coupled plasma mass spectrometry

At present, there is some concern as regards the release of Pt from catalytic converters for automotive exhaust control. These catalysts, in fact, can release particulate Pt and other metals, such as Pd and Rh, into the environment through combined mechanical and thermal effects. The increasing emission of Pt-group metals has led to a growing need for suitable analytical procedures for their determination at very low levels in biological and environmental matrices. In this context, a method is described which is based on the use of a magnetic sector field inductively coupled plasma–mass spectrometry (ICP–MS) for the determination of Pd, Pt and Rh at ng l−1 levels in urine preliminarily digested by UV irradiation. Several sample pretreatment approaches were tested. The adverse effect of potentially interfering species on the mass-spectrometric determination of these metals was also taken into account. In particular, the role of other concomitants, such as Cd, Cu, Mo, Pb, Rb, Sr and Zn, was investigated in detail. The influence of such elements on the isotopes of interest, i.e. 106Pd, 195Pt and 103Rh, was quantified as apparent mean concentrations produced by the interfering elements at the expected levels in urine. These turned out to be in the 0.003–3.5 ng l−1 range. The data obtained demonstrated that the effects of 106Cd and 40Ar66Zn on 106Pd as well as of 206Pb2+, 87Sr16O and 40Ar63Cu on 103Rh cannot be disregarded. Detection limits in UV-digested and 1 : 20 diluted urine were found to be 0.25, 0.03 and 0.03 ng l−1 for 106Pd, 194Pt and 103Rh, respectively, in the low resolution mode in conjunction with ultrasonic nebulization. Repeatability of measurements was always better than 3%, while recovery data were in good agreement with the expected values. The method was tentatively applied to urine samples of 30 youngsters from the urban and suburban area of Rome. The findings allow the Pt level of these subjects to be defined at or below 1 ng l−1 and the Pd and Rh contents at ca. 10 ng l−1.