Quantitative Determination of Au, Pt, and Pd in Soil and Stream Sediment Samples by GF-AAS and ICP-MS

摘要

A combined method has been developed for the determination of gold (Au), platinum (Pt), and palladium (Pd) in soil and stream sediment samples, based on closed vessel aqua regia digestion and solvent extraction by MIBK (methyl isobutyl ketone), followed by analysis with GF-AAS (graphite furnace atomic absorption spectrometry) and ICP-MS (inductively coupled plasma mass spectrometry). Matrix reduction prior to aqua regia digestion, solvent extraction after complex formation, and determination up to ppb levels are the key features of this method. The roasted sample was digested with (1:1) HCl in the closed vessel polytetrafluoroethylene (PTFE), filtered, and the residue digested with aqua regia. The content was evaporated to dryness and taken in dilute HCl. Gold was first extracted from this solution with pre-equilibrated methyl isobutyl ketone (MIBK), then determined by GF-AAS using a standard procedure. The Pt and Pd were extracted from the raffinate (residual aqueous solution) by another portion of pre-equilibrated MIBK after complexing with the thiocyanate ligand. Both elements were quantitatively determined by ICP-MS after stripping with dilute HNO3 from the loaded organic phase. Recoveries were found to be around 95% for all of the elements. The limit of quantitation (10 sigma achieved for Au, Pt, and Pd was 1.0, 0.5, and 1.0 ng/g, respectively. This method has been developed using eight certified reference materials (CRMs) of soil and stream sediment samples of different origin. The efficiency of the proposed method was evaluated by analyzing eight real soil and stream sediment samples collected by the Geological Survey of India.