The development of a high accuracy method for the analysis of Pd, Pt and Rh in auto catalysts using a multi-collector ICP-MS

Abstract

Catalysts containing the platinum group elements (PGEs) are employed for a variety of industrial and chemical uses. Palladium (Pd), platinum (Pt) and rhodium (Rh) are the active components in automobile catalytic converters as well as catalysts used in pharmaceutical/biological applications and petroleum refining. In all cases the high economic value of these catalysts means that it is important to be able to measure the precious metal loading very accurately. The aim of this work was to develop a robust and reliable high accuracy/precision method for the analysis of Pd, Pt and Rh metals in autocatalysts with a target expanded uncertainty (i.e., k = 2, 95% confidence) of approximately 1% relative. A microwave digestion procedure was developed that provided a relatively quick total dissolution of the precious metals in a 0.2 g sample. An ultrasonic nebuliser with desolvation enabled the effects of the key interferences to be negated. Thus it was possible to make the comparison between a multi-collector ICP-MS and a more conventional quadrupole instrument. For Pd and Pt, high accuracy analysis was underpinned by an approximate matching isotope dilution calibration procedure. In the case of monoisotopic Rh an approximate matching bracketing calibration procedure was used (which had originally been developed for high accuracy ICP-OES) with Ru as the internal standard. Using the procedures reported here, the multi-collector ICP-MS provided data for the NIST autocatalyst reference material (SRM 2556) which showed excellent agreement with the reference values for Pd, Pt and Rh, with expanded uncertainties (i.e., k = 2, 95% confidence) of 0.9%, 1.1% and 0.9%, respectively. The equivalent data from the conventional quadrupole ICP-MS shows an approximately two-fold increase in these uncertainty estimates. Such a difference is likely to be very significant when dealing with these very precious materials which have a very high intrinsic economic value.