Determination of copper in high-purity niobium, tantalum, molybdenum and tungsten metals with bathocuproïne

A spectrophotometric method for determining 0.0005–0.125% of copper in high-purity niobium, tantalum, molybdenum and tungsten metals is described. After sample dissolution and reduction of copper to the univalent state with ascorbic acid, the yellow complex formed by copper I and bathocuproine (2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline) is extracted into n-amyl alcohol and the absorbance of the resulting extract is determined at 476 mμ. Other impurities present in the four high-purity metals described do not interfere in the proposed method.