The extraction and spectrophotometric determination of niobium with tetraphenylarsonium chloride

A rapid and accurate spectrophotometric method for niobium is described. Tetraphenylarsonium chloride is used to form an aqueous insoluble ion-pair, tetraphenylarsonium thiocyanato-niobate, which upon extraction into 9:2 chloroformacetone solution has a molar absorptivity of 36,000/M/cm at 390 nm. Niobium is masked with fluoride before a separation step in which the interferences of molybdenum, tungsten, and iron are removed by reduction and extraction. Niobium is subsequently extracted after being demasked with boric acid. The method has been applied successfully to 3 NBS steels and 2 heat-resisting alloys.