A method has been developed for the determination of microgram levels of Pt, Pd, Rh, and Au. A 10-mg Ag bead containing the precious metals, as extracted by fire assaying, is arced at 8 A dc in graphite electrodes in the presence of 10 mg of either Rh or Pt metal powder. The matrix elements, Ag and Pt, or Rh, serve as internal standards, and intensity ratios Pt/Rh or Rh/Pt, Pd/Rh, and Au/Ag are determined. Precision of the method is about ±5% coefficient of variation for Pt and Rh, ±15% for Pd, and ±19% for Au. Limits of detection are below 1 μg, giving analysis limits (for a 1-assay-ton sample) of about 1–30 ppb for these precious metals.
