Preconcentration of noble metals on alumina prior to analysis by inductively coupled plasma mass spectrometry: Application to geological samples.

A preconcentration method for the determination of noble metals (Ag, Au, Ir, Os, Pd, Pt, Re, Rh, Ru) was developed using alumina as a sorbent. The method involves an off-line preconcentration analytical procedure: the formation of chloro-complexes of these elements with HCl, loading of the chloro-complexes on alumina followed by elution of analytes and analysis by inductively coupled plasma mass spectrometry. The effects of HCl/HNO concentration in the sample digest, mass of alumina, and concentration of eluents (HCl and HNO)/thiourea were studied using multivariate experimental designs. Using 2 M HCl as eluent, detection limits were improved by a factor of 10-20 for Ag, Ir, Os, Pd, Pt, and Ru, and 3-5 for Re and Rh compared to those achieved by direct nebulization (i.e. without preconcentration). Accuracy was verified through analysis of CDN-PGMS-19 ore reference material. Using 2 M HCl for elution, the results for Ag, Pd and Pt agreed with the reference values obtained based on aqua regia digestion (which does not achieve total dissolution). For the determination of Au, evaporation of HNO and elution with thiourea were required.