Analysis of refined silver and platinum by inductively coupled plasma atomic emission spectrometry

National and international standards for analysing refined silver and platinum using ICP–AES are reviewed. Significant weaknesses in the existing standards for silver and platinum analysis have been identified, including incorrect selection of analytical lines for the elements to be determined and lengthy, labour-intensive and economically unfavourable methods of sample preparation for analysis. These deficiencies lead to doubtful results in the certification of aluminium, silicon and rhodium contents in silver reference samples. Original schemes of silver and platinum dissolution in closed tubes in systems with bottom resistance heating have been developed. The best way to prepare silver samples is to dissolve them in a mixture of HNO3 + HF and, if the Au content is higher than 20 ppm, to separate the solution over the precipitate. To dissolve 1 g of platinum, 6 cm3 of HNO3 and HCl mixture is sufficient. A new approach to the preparation of basic gold solutions in chloric acid has been developed which allows gold and silver solutions to be mixed together and calibration curves to be used not only for solution analysis but also for direct assay of silver without dissolution. Alternatively, silver and platinum can be analysed using a spark sampling accessory. The optimum instrumental parameters for performing the assay are the use of an in-house standard combined with a lower plasma discharge. For silver and platinum contents of less than 99.99% in samples, the maximum accuracy of the assay is achieved by using a calibration based on concentration ratios. Reference samples of silver and platinum powder have been analysed.