Spectrophotometric determination of molybdenum in steel with thiocyanate and tetraphenylarsonium chloride

An alternative procedure is described for the colorimetric determination of molybdenum in steel. Molybdenum(VI) is reduced to molybdenum(V) with ascorbic acid and titanium(III) before being caused to react with thiocyanate and extracting it with tetraphenylarsonium chloride into chloroform that contains quinol. The procedure is sensitive (εmax.= 17 400 l mol–1 cm–1 at 470 nm) and precise. A forty-fold excess of tungsten over molybdenum can be tolerated. Results for a series of low-alloy and tungsten tool steels are reported.