Platinum is mainly used for catalytic converters, jewellery, dental protheses and electronics. The catalyst sector is divided into automotive catalysts and catalysts for chemical synthesis. The former are responsible for the majority of anthropogenic platinum emissions into the environment, the latter for impurities in pharmaceuticals and other products. Isotope dilution mass spectrometry (IDMS) is often used to quantify traces of platinum in the environment, pharmaceuticals, and other samples as it offers unrivalled advantages, such as insensitivity to analyte loss during sample preparation, insensitivity to matrix effects and low achievable measurement uncertainty. One obstacle with IDMS is the availability of calibrated spike solutions and of isotope reference materials when isotope variation occurs. The first issue is solved with ERM-AE141, a certified ¹⁹⁴Pt spike solution, and the second issue should have been solved with IRMM-010, a certified isotope reference material for platinum. In addition to the pure concentration measurement of platinum emissions, source tracing based on isotope ratio or more precisely delta measurements can also be carried out. However, this requires an isotope reference material. Finally, improving the atomic weight and consequently the molar mass of platinum requires more accurate measurements.

In principle, a certified isotope reference material such as IRMM-010, should fulfil all these needs and requirements. However, 25 years ago, when IRMM-010 was characterized, the desired uncertainty levels of today could not be achieved, especially for the isotope amount fractions of the minor abundant Pt isotopes ¹⁹⁰Pt and ¹⁹²Pt. This situation has since been observed in several reference measurements, e.g., in the characterization of the Pt spike ERM-AE141 or in the reference measurement of Pt mass fractions in automotive catalytic converters. One workaround was to calculate the K-factors for the isotope ratios of the low abundant isotopes, e.g., ¹⁹⁰Pt/¹⁹⁵Pt and ¹⁹²Pt/¹⁹⁵Pt, via that for ¹⁹⁴Pt/¹⁹⁵Pt by applying the exponential law. This, however, is only a short-term remedy or workaround, but not a real solution.

Therefore, a joint effort was made to recharacterize the still existing Pt isotope reference material IRMM-010. The absolute platinum isotope ratios are determined by applying four different approaches. Firstly, the K-factors are obtained from the gravimetric mixture approach in which isotope mixtures of the enriched isotopes ¹⁹⁴Pt, ¹⁹⁵Pt, and ¹⁹⁸Pt are prepared to calibrate the mass spectrometer. Second, the K-factors are calculated from the ²⁰³Tl/²⁰⁵Tl isotope ratio in NIST SRM 997 by applying the exponential law. Third, the K-factors are calculated from the ²⁰⁶Pb/²⁰⁸Pb isotope in NIST SRM 981 by applying the exponential law. Fourth, the mass bias regression model is applied to the simultaneously measured platinum isotope ratios of IRMM-010 and Pb isotope ratios of NIST SRM 981. The first results of the four approaches obtained on several MC-ICP-MS instruments will be presented and compared.