Ultratrace Platinum Group Elements in Geological Samples by Inductively Coupled Plasma-Mass Spectrometry with Nickel Sulfide Fire Assay

Pt, Pd, Rh, Ir, Os and Ru are platinum group elements (PGEs) with similar properties. Due to the low abundance as well as the nugget effect, the accurate determination of PGEs has been a challenge for rock and mineral analysis. Fire assay methods with large sample weights were developed to separate and preconcentrate PGEs, however, there are still difficulties to accurately determine ultratrace PGEs because of the high reagent blanks and the matrix effect. A method of nickel sulfide fire assay combined with ICP-MS simultaneous determination of ultratrace PGEs in samples was established. The results showed that the blank mainly comes from hydrochloric acid and nickel collector when using nickel sulfide fire assay to capture PGEs. The intensities of PGEs were detected by ICP-MS in standard mode and kinetic energy discrimination. In standard mode, the detection limits were 0.2ng/g for Pt and Pd, and 0.02ng/g for Rh, Ir and Os, but it couldn’t reach 0.1ng/g for Ru. In kinetic energy discrimination, the background equivalent concentration of Ru was two orders of magnitude lower than that in the standard mode. With the matrix effect of Ni effectively eliminated, the detection limits reached 0.005ng/g for Ru. The detection limits for PGEs required by geochemical exploration were achieved. The certified reference materials of soil (GBW07288, GBW07294) and stream sediment (GBW07289) were analyzed to test the method. The determined values were in good agreement with the certified values. The relative errors were between −10.9% and 11.8%, the relative standard deviations (RSD, n=12) were 3.88%−9.37%, and the spiked recoveries were 92%−110%. This method is simple, rapid and meets the requirements of ultratrace PGEs determination in large quantities of geological samples. The BRIEF REPORT is available for this paper at http://www.ykcs.ac.cn/en/article/doi/10.15898/j.ykcs.202407180159.