Analysis of Pd, Pt, and Au at XRAL Laboratories by Fire Assay - Atomic Absorption Spectrometry. Gold, Pd, and Pt are determined by DCP or atomic absorption spectrophotometry after collection by fire assay. An assay fusion consists of heating a mixture of the finely pulverized sample with about three parts of a flux until the product is molten. One of the ingredients of the flux is a lead compound which is reduced by other constituents of the flux or sample to metallic lead. The latter collects all the gold, together with silver, platinum metals, and small quantities of certain base metals present in the sample and falls to the bottom of the crucible to form a lead button. The gangue of the ore is converted by the flux into a slag sufficiently fluid so that all particles of lead may fall readily through the molten mass. The choice of a suitable flux depends on the character of the ore. The lead button is cupelled to oxidize the lead leaving behind a dore bead containing the precious metals. The dore bead is then transferred to a test tube, dissolved with aqua regia, diluted to a specific volume and determined by DCP or atomic absorption spectrophotometry.
The lower reporting levels for Au, Pt, and Pd, respectively, are 5, 10, and 1 ppb for a 15 g sample charge by DCP and atomic absorption. The upper reporting limit is 10,000 ppb.