A method is presented for the determination of microgram levels of Ir, Ru, and Os in ores, concentrates, and heavy sands. Radiotracers are used to monitor the recovery of these three metals in a 10-mg Pt bead during the normal fire assaying procedure. The Pt bead is arced at 20 A dc in a graphite electrode, and Pt serves as an internal standard. The precision of the method for Ir, Ru, and Os is about 5, 10, and 22% coefficient of variation, respectively. If high accuracy is not required, empirical correction factors may be applied for the assay losses of Ir and Ru, thereby eliminating the need for radiotracers.
K. G. Broadhead, B. C. Piper, and H. H. Heady, "Fire Assay-Emission Spectrographic Determination of Iridium, Ruthenium, and Osmium," Appl. Spectrosc. 26, 461-467 (1972)