Determination of trace amounts of niobium in steel by reversed-phase high-performance liquid chromatography with methyl isobutyl ketone extraction and pre-column derivatization

A method for the determination of trace amounts of niobium in steel samples by reversedphase high-performance liquid chromatography (RP-HPLC) was developed. The iron matrix was removed from sample solution by using methyl isobutyl ketone as an extraction agent. 2(5-Bromo-2-pyridylazo)-5-diethylamino phenol (5-Br-PADAP) was used as a pre-column chelating agent to form ternary complex with Nb(V) and tartaric acid. The Nb(V) complex was eluted within 3min with a mobile phase of methanol-water (56:44 (v/v)) containing 10mmol/l acetate buffer (pH 3.5) on a C18 column and determined with spectrophotometric detection at 600nm. The detection limit of this method for Nb in iron or/and steel sample was 0.015µg/g. The proposed method was applied to the analysis of trace amounts of niobium in cast iron.