Platinum, palladium, and rhodium are determined by direct spectrographic analysis of a 4 mg gold bead obtained by fire assay fusion and cupellation. The weighed bead is placed into a graphite electrode containing 2 mg of (NH4)2 OsCl5 which stabilizes the platinum volatilization and is burned in a 15 A dc arc in an argon–oxygen atmosphere. Detection limits for a sample of one assay ton are 5 ppb for Pt and less than 1 ppb for Pd and Rh.
Anthony F. Dorrzapf and Floyd W. Brown, "Direct Spectrographic Analysis for Platinum, Palladium, and Rhodium in Gold Beads from Fire Assay," Appl. Spectrosc. 24, 415-418 (1970)