The spectrophotometric determination of tungsten with thiocyanate. Part II. An experimental assessment of procedures: a recommended procedure for the determination of tungsten in steel

Abstract

The precision, sensitivity, colour stability and selectivity of several procedures for the spectrophotometric determination of tungsten with thiocyanate have been compared.

An extraction procedure in which tetraphenylarsonium or similar ions are used for the determination of tungsten in steel has been developed, which has shown consistent reliability when applied to a wide range of tungsten steels, and which is completely free from interference by vanadium. The concentration of iron in the aqueous solution from which the tungsten is extracted determines the extent of interference by molybdenum. When the recommended sample size and dilution factors are used, 0·3, 3·0, 12, 60 and 97·5 per cent. w/w of molybdenum can be tolerated for tungsten in the ranges up to 0·25, 0·25 to 0·5, 0·5 to 1·25, 1·25 to 2·5 and 2·5 to 25 per cent. w/w, respectively. The tolerances in the lower tungsten ranges can be increased if necessary by using a higher dilution factor and accepting a lower absorbance reading.