Determination of trace platinum and palladium in geochemical sample by laser ablation-inductively coupled plasma mass spectrometry with lead fire assay
In this paper,a novel method for the determination of trace platinum(Pt)and palladium(Pd)in geochemical samples by lead fire assay(Pb-FA)enrichment and laser ablation-inductively coupled plasma mass spectrometry(LA-ICP-MS)was reported.The self-made and purified basic lead carbonate was used for the separation of Pt and Pd.Pt and Pd were enriched into silver(Ag)composite granule by cupellation with Ag protection.The Ag granule was cleaned,weighted,annealed and compressed into thin slices,and then determined by LA-ICP-MS via direct solid sampling with multipoint ablation(10 points).195Pt,105Pd and 109 Ag were selected as the isotopes to be measured.The determination of trace Pt and Pd in geochemical samples was realized by quantification via empirical coefficient method and internal standard method.The experiments showed that when the self-made and purified basic lead carbonate was used as the collector,the measured blank values of Pt and Pd reduced by two orders of magnitudes compared to lead oxide.The blank values of Pt and Pd in lead fire assay were reduced significantly.The certified reference materials of platinum family elements were for the preparation of Ag slices to draw the calibration curves,which real-ized the matrix matching of certified reference materials and actual samples,thus overcoming the matrix effect.The direct solid sampling of laser ablation Ag slices avoided the polyatomic molecular and ion mass spectrum interference caused by much O,H and Cl in solution as well as the dilution effect caused by solu-tion preparation.If the Ag granule was ignited at 700 ℃ followed by annealing and sample preparation,the determination signals of 195Pt and 105Pd after laser ablation for several times were more stable,which could eliminate the structure defects and improve the uniformity of granule.The calibration curve was drawn u-sing the mass spectrum intensity ratio of 195Pt and 105Pd against 199 Ag as the y-coordinate,and using the content of Pt and Pd in Ag slice as the x-coordinate.The correlation coefficients were 0.999 7 and 0.999 6,respectively.The limits of detection were 0.066 ng/g and 0.028 ng/g(for 10 g of sample),respectively.The proposed method was applied for the analysis of trace Pt and Pd in various types of geochemical sam-ples.The relative standard deviations(RSD,n=5)of determination results of Pt and Pd were 4.5％-13.9％and 4.8％-10.7％,respectively.The found results were well consistent with those obtained by lead fire assay-high resolution continuum source graphite furnace atomic absorption spectrometry.The contents of trace Pt and Pd in certified reference materials of geochemical sample were determined according to the experimental method,and the results were consistent with the certified values.
lead fire assay(Pb-FA)silver protection cupellationempirical coefficient methodlaser abla-tion-inductively coupled plasma mass spectrometry(LA-ICP-MS)platinumpalladium
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