Direct determination of Pd, Pt and Rh in fire assay lead buttons by laser ablation-ICP-OES: automotive exhaust catalysts as an example

Abstract

The increasing use of Pd, Pt and Rh as catalysts in industrial applications results in the necessity of fast and accurate methods for the determination of these elements, not only in natural sources, but also in recyclable materials, such as spent automotive exhaust catalysts. Because of the low Pd, Pt and Rh contents in the samples typically analyzed and in order to avoid the influence of matrix components and sample heterogeneity, trace/matrix separation by means of lead fire assay usually precedes the actual analysis. This article concentrates on the determination of Pd, Pt and Rh in lead buttons obtained via fire assay using laser ablation-optical emission spectrometry. A 266 nm Nd:YAG-based laser ablation unit offering a maximum laser beam diameter of 780 μm was coupled to an ICP-OES instrument permitting simultaneous monitoring of the entire spectrum owing to the use of linear CCD detectors mounted on a Rowland circle of a spectrometer in Paschen-Runge mounting. Matrix-matched standards were applied for the construction of calibration curves, which were subsequently used for analysis of some real-life samples. The three different acquisition methods available were evaluated, but turned out to be quite similar in terms of linearity, accuracy and detection power. All but two of the resulting regression coefficients of the calibration curves were ≥0.999, while, taking into account their uncertainty, the experimental results are in good agreement with the reference values (obtained via wet chemical analysis) for the real-life samples analyzed, Pb buttons prepared by fire assay of an automotive exhaust catalyst. Limits of detection vary between 2.5 and 12 μg g⁻¹ in the Pb button and the method precision was shown to be typically better than 5%.