Determination of cobalt, nickel, lead, bismuth and indium in ores, soils and related materials by atomic-absorption spectrometry after separation by xanthate extraction

A method for determining approximately 0.5, mug/g or more of cobalt, nickel and lead and approximately 3 mug/g or more of bismuth and indium in ores, soils and related materials is described. After sample decomposition and dissolution of the salts in dilute hydrochloric-tartaric acid solution, iron(III) is reduced with ascorbic acid and the resultant iron(II) is complexed with ammonium fluoride. Cobalt, nickel, lead, bismuth and indium are subsequently separated from iron, aluminium, zinc and other matrix elements by a triple chloroform extraction of their xanthate complexes at pH 2.00 +/- 0.05. After the removal of chloroform by evaporation and the destruction of the xanthates with nitric and perchloric acids, the solution is evaporated to dryness and the individual elements are ultimately determined in a 20% v/v hydrochloric acid medium containing 1000 mug/ml potassium by atomic-absorption spectrometry with an air-acetylene flame. Co-extraction of arsenic and antimony is avoided by volatilizing them as the bromides during the decomposition step. Small amounts of co-extracted molybdenum, iron and copper do not interfere.