Alternatives to the fire assay procedure for the preparation of automobilecatalyst samples prior to analysis

To ensure reliable results for precious metal (PM) determinations, where th e metals are unevenly distributed through the matrix, adaptations of the fi re-assay procedure are normally used for sample preparation. Fire assay for precious metals usually refers to a process in, which the assay portion of a sample (usually from 10 - 30 g) is heated with a flux containing either litharge or nickel sulphide. The complete process is complex, very time-con suming and labour intensive, and so alternative methods of sample preparati on have been sought for many years (I). An open-beaker digestion method (I) , a microwave-assisted pressure digestion method (II) and a sodium peroxide fusion method (III) are described for the dissolution of automobile exhaus t catalyst samples prior to their analyses for platinum, palladium and rhod ium by ICP-MS. Sample sizes varied between 0.1 and 0.25 g. Analyses were pe rformed on a Perkin-Elmer Elan 6000 ICP-MS with indium and iridium as inter nal standards. With Methods I and II, good recoveries (similar to 100%) wer e achieved for platinum and palladium, but the rhodium recoveries (similar to 90%) were unsatisfactory. However, with Method III, excellent recoveries (similar to 100%) were found for all three elements and its introduction l ed to a reduction in cost (labour and materials) from $350 to $35 per sampl e.