Inductively coupled plasma time-of-flight mass spectrometry (ICP-TOFMS) with desolvating sample introduction and He collision gas for high-accuracy determination of Rh, Pd and Pt in automobile catalytic converters

Abstract

A novel and selective method has been developed for high-accuracy determination of Pd, Pt and Rh in complex autocatalyst matrices using isotope dilution (ID) analysis (for Pt and Pd) and internal standard (IS) matching (for Rh) with ICP-time-of-flight mass spectrometry (ICP-TOFMS). By using a desolvating inlet interface and He collision gas, spectral interferences on selected isotopes (e.g., ¹⁰⁵Pd, ¹⁹⁵Pt, ¹⁹⁶Pt) were successfully removed. Calibration is performed by exact-matching ID analysis for Pd (¹⁰⁴Pd/¹⁰⁵Pd) and Pt (¹⁹⁶Pt/¹⁹⁵Pt) and IS matching with ¹⁰¹Ru for monoisotopic ¹⁰³Rh. Due to the quasi-simultaneous determination of all the isotopes of interest by ICP-TOFMS, isotope ratio precision was improved in comparison with that of sequential instrumentation, thus leading to reduced measurement uncertainties of <1% (k = 2), as required by autocatalyst manufacturers. This represents an approximately 2–3-fold improvement for Rh and Pd and 6-fold improvement for Pt in comparison to the uncertainties achieved using the same measurement strategy for sequential ICP-MS instrumentation. The method has been applied to the characterisation of a candidate CRM LGC3101 (unused automobile catalyst) containing high levels of Zr and Hf and validated by the analysis of similar matrix CRMs and by participation in an interlaboratory exercise.