Determination of trace platinum in geochemical sample by isotope dilution-laser ablation inductively coupled plasma mass spectrometry with antimony fire assay
The content of platinum is usually determined by inductively coupled plasma mass spectrometry(ICP-MS)after enrichment by fire assay.The assay button should be dissolved for determination,so the operation is complicated and there is solution dilution effect.In this study,194Pt isotope diluent was added into the sample,and platinum was separated and enriched by antimony fire assay.The antimony composite granule was obtained after cupellation and then polished to antimony slice with smooth surface.The iso-tope ratio(195 Pt/194 Pt)was determined by laser ablation inductively coupled plasma mass spectrometry(LA-ICP-MS).The content of platinum was quantified according to the formula of isotope dilution meth-od.Thus,a determination method of trace platinum in geochemical samples was established with direct solid sampling after fire assay enrichment.The experiments showed that when self-purified antimony oxide was used as collector agent and high purity quartz crucible was used instead of traditional fire assay clay crucible,the blank value of platinum in antimony fire assay process could be reduced to 0.52 ng,which broke the bottleneck of high blank value for platinum in fire assay process.LA-ICP-MS planar imaging re-sults showed that the distribution of 194Pt and 195Pt in antimony slice was not uniform,but the rules were similar for the trend of uneven distribution.LA-ICP-MS was used for the further multipoint ablation of 194Pt and 195Pt in antimony slice.The results showed that the relative standard deviations(RSDs,n=6)of mass spectral intensity of 194 Pt and 195 Pt were 14.7％and 14.1％,respectively.However,for the mass spectral intensity ratio of 195Pt and 194Pt,the RSD was 2.5％,indicating that platinum in isotope diluent had been fully exchanged with that in geochemical samples.The proposed method was applied for determi-nation of platinum in geochemical certifeid reference materials,and the results were basically consistent with the certified values.The RSDs(n=6)of determination results were between 2.0％and 5.1％.The proposed method realized the determination of platinum in geochemical samples by solid-solid combined a-nalysis technique(solid high temperature melting enrichment-laser ablation direct solid sampling)and iso-tope dilution.
antimony fire assayplatinumisotope ratiohigh purity quartz crucibleisotope dilutionlaser ablation inductively coupled plasma mass spectrometry(LA-ICP-MS)
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