Preconcentration of traces of silver and bismuth from cobalt and nickel and their nitrates, with activated carbon

A method is described for the preconcentration of trace metals Ag and Bi, present as impurities in high-purity cobalt and nickel metals and their nitrates. After the metal samples have been dissolved in nitric acid (or the salts in water) the trace elements are complexed with ammonium pyrrolidinedithiocarbamate (APDC). The sample solution is then filtered through a 2-cm filter paper coated with 50 mg of activated carbon, whereby the complexed trace metals are adsorbed on the activated carbon and separated from the matrix. The trace elements are dissolved off with nitric acid and determined by flame atomic-absorption spectrometry (AAS). The detection limits for the analysis of 10 g of metal samples and 50 g of the nitrate samples were 0.002-0.035 ppm Ag and 0.04 ppm Bi for the metal samples, and 0.0003-0.0004 ppm Ag and 0.004-0.005 ppm Bi for the nitrate samples. The coefficient of variation, in general, is 10-25% for Ag and 33% for Bi.