A critical evaluation of spectrographic, fluorescent X-ray, and polarographic methods for the determination of the platinum metals

Abstract

This review covers pertinent publications up to June 1958. The methods are evaluated from the point of view of their analytical applications to assay beads and buttons, platinum metal precipitates, and alloys of platinum metals with and without base metal impurities. No spectrographic method has been recorded for the direct determination of platinum metals in ores or concentrates. For the determination of palladium, platinum and rhodium in ores and concentrates the most accurate spectrographic methods involve a preliminary fire assay extraction to produce a lead button or a silver bead. For these, and for other alloys, precipitates, etc. the most accurate methods involve special efforts to produce uniformity of composition and to produce standards with identical metallurgical histories. No successful spectrographic method has been recorded for either the direct or indirect determination of iridium, ruthenium and osmium in ores, concentrates or complex alloys. None of the frequent claims that spectrographic methods produce greater accuracy than wet methods has been substantiated and all are unacceptable. The few existing data indicate that with competent analysts and under optimum conditions the accuracies of the two methods are comparable. For the qualitative examination of the purity of precipitates etc. containing a variety of metal traces the spectrographic method is incomparably superior to wet methods. Polarographic methods for the platinum metals have been confined to systems with few constituents. No procedure has been recorded for the successful application to assay beads or buttons. Few detailed procedures have been recorded for the determination of any platinum metal and no method includes the usual processes of securing dissolution of multicomponent systems. Undoubtedly, polarographic methods could be useful competitors in areas below those in which classical methods apply. Furthermore, both spectrographic and polarographic methods provide the great advantage of speed when applied to large numbers of samples whose compositions are not widely different. Too few X-ray spectrographic procedures have been recorded to estimate relatively their accuracy and precision.