Determination of platinum, palladium, ruthenium and iridium geological materials by inductively coupled plasma mass spectrometry with sample introduction by electrothermal vaporisation

The application of electrothermal vaporisation as a means of sample introduction for the determination of some of the platinum group metals by inductively coupled plasma mass spectrometry (ICP-MS) has been studied. Rock powders were decomposed using the nickel sulphide fire assay technique. Samples of 10 g were pre-concentrated to a final solution volume of 0.5 ml. Sample solutions were analysed for the platinum group elements using the method of stable isotope dilution. Optimum plasma operating conditions were found to be different for the determination of the platinum group metals when dry aerosols were introduced into the plasma or when solution nebulisation was used. Pyrolytic graphite coated crystalline filaments were used for the vaporisation of acidic sample solutions. The addition of 500 p.p.m. of Ni as nitrate resulted in up to a ten-fold enhancement in the analyte ion count rate. A smaller effect was observed for Cu for which the nitrate was more effective than the chloride for producing signal enhancements. The addition of 500 p.p.m. of Ni as nitrate was used as a matrix modifier for the determination of the platinum group elements in geological materials. Quantitative analytical data for a series of ultramafic rock samples determined by neutron activation analysis, solution nebulisation ICP-MS and electrothermal vaporisation ICP-MS compared well with one another.