Determination of trace metal impurities in high purity silver by two step selective precipitation separation followed by neutron activation analysis

Abstract

A neutron activation analysis method for the determination of Au, Co, Cu, Fe, Hg and Zn in high purity silver materials with prior isolation of the analytes by a two-step selective precipitation separation from the silver matrix was developed. In the first step, the silver matrix was separated from the trace impurities of interest through the addition of hydrochloric acid to form a silver chloride precipitate. The principle of this separation is based on the extreme difference in the solubilities of the chlorides of silver and the trace elements of interest. In the second step, the trace elements remaining in the solution were subsequently coprecipitated with the Pb salt of pyrrolidine dithiocarbamate, Pb(PDC)₂. The concentrations of six elements (Au, Co, Cu, Fe, Hg and Zn ) collected in the precipitate were determined by neutron activation analysis. Limits of detection of 0.001, 0.1, 0.08, 10, 0.1 and 1 µg g^–1 for Au, Co, Cu, Fe, Hg and Zn, respectively, were obtained. The proposed method was validated by the analysis of NIST SRM 8171 Fine Silver and applied to the determination of metal impurities in two high-purity silver samples (EM9465 and EM9343).