Interference free ultra trace determination of Pt, Pd and Au in geological and environmental samples by inductively coupled plasma quadrupole mass spectrometry after a cloud point extraction

Abstract

A simple and efficient cloud point extraction procedure has been described for the pre-concentration and separation of ultra trace levels of Pt, Pd and Au simultaneously from geological and environmental samples for their determination by inductively coupled plasma quadrupole mass spectrometry (ICP-QMS). The method is based on the formation of hydrophobic complexes of Pt, Pd and Au with N,N-dihexyl-N′-benzoylthiourea in presence of an HCl medium, followed by their extraction, into a small volume of surfactant rich phase, using a non-ionic surfactant Triton X-114. The main parameters affecting the extraction process such as type and concentration of complexing agent and acids, and also the amount of Triton X-114 are optimized, which is also useful for alleviation of spectral interferences. The recoveries of analytes in the absence and presence of 4 μg mL⁻¹ of interfering elements such as Zr, Y, Sr, Hf and Ta from road dust digest are in the range 98–105%. This indicates the effective alleviation of interfering ions. The pre-concentration factors are 100, 104 and 105, respectively, for Pt, Pd and Au with a relative standard deviation of 0.1–3.0% at 50 pg mL⁻¹. The limits of detection for seawater and road dust samples are 0.01, 0.01 and 0.15, and 3.1, 4.4 and 44 pg g⁻¹, respectively, for Pt, Pd and Au. The accuracy of the procedure is verified by analyzing certified reference materials such as BCR CRM 723 (road dust) for Pt and Pd, and NIST SRM 2709 (San Joaquin soil) for Au, and also by applying it to road dust samples collected locally.