Analytical studies of metal thiocyanate complexes

Some onium compounds react with thiocyanate complex anions to give stable coloured salts, which can be extracted into organic solvents. This generally results in an increase in the apparent molar absorptivity of the thiocyanate complexes and in their stability. Reactions of thiocyanate complexes of molybdenum, niobium, and rhenium with tetraphenylarsonium compounds have been critically studied in an attempt to improve existing methods for determining trace amounts of these metals. A method has been developed for the determination of trace amounts of molybdenum in steels or in other matrices. The optimal conditions for the formation of the thiocyanate complex and for its extraction were determined. Because of the high sensitivity, accuracy and precision of the procedure, it is considered to be superior to other chemical methods for the quantitative determination of molybdenum in steels. Fifteen metals commonly found in steels were shown not to interfere with the determination of molybdenum. Tungsten and niobium however, do interfere, but can readily be masked with oxalic acid. A forty-fold ratio of tungsten to molybdenum can be tolerated. [Continues.]