Extraction-spectrophotometric determination of niobium with N-phenylbenzohydroxamic acid and 4-(2-pyridylazo)resorcinol in non-aqueous media

Abstract

A method for the spectrophotometric determination of niobium(V) is proposed, in which niobium(V) is extracted with N-phenylbenzohydroxamic acid into chloroform from 5 M hydrochloric acid. The colour is then developed in an aliquot of the chloroform extract by addition of 4-(2-pyridylazo)resorcinol solution in N,N-dimethylformamide without back-extraction. The molar absorptivity at 547 nm is 3.35 × 10⁴ l mol^–1 cm^–1 with a relative standard deviation of 1.0%. The proposed method permits the determination of niobium(V) at trace levels in the presence of large amounts of other ions. The method has been applied to the determination of niobium in BCS standard steels and ores (IGS standard culombites) and high accuracy and precision have been obtained.