Abstract
A spectrophotometric method for determining iron in the range 0·001–0·125% in high-purity niobium, tantalum, molybdenum and tungsten metals is described. After sample dissolution and reduction of iron to the bivalent state with ascorbic acid and hydroxylamine hydrochloride, the red complex formed between iron II and bathophenanthroline (4,7-diphenyl-1,10-phenanthroline) is extracted into n-arnyl alcohol and the absorbance of the resulting extract is determined at 536 mμ. Interference from copper is eliminated with thiourea. Cobalt, cadmium, nickel, manganese and zinc also interfere but the amounts of each of these impurities present in the four high-purity metals described are so low that their interference effects are negligible in the proposed method. Highly reproducible and precise results can be obtained with careful control of the pH during reduction and extraction.
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