Fire-assay emission spectrographic method for platinum, palladium, rhodium, and gold.
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 10 a DC in graphic 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 percent coefficient of variation for pt and rh, +/-15 percent for pd, and +/- 19 percent for au. Limits of detection are below 1 ug, giving analysis limits (for a 1-assay-ton sample) of about 1 to 30 parts per billion for these precious metals.