Speciation of vanadium(V) and vanadium(IV) with 4-(2-pyridylazo) resorcinol by using high-performance liquid chromatography with spectrophotometric detection

By using 4-(2-pyridylazo)resorcinol (PAR) as the chelating reagent, vanadate and vanadyl ions were effectively separated by reversed-phase high-performance liquid chromatography with ultraviolet–visible detection at 540 nm. The optimum conditions for the determination of these metal ions were established. PAR chelates were eluted within 10 min with methanol–water (30 + 70 v/v) as the mobile phase containing acetate buffer (8.0 × 10–3 mol l–1, pH 6.0) and PAR (3.0 × 10–4 mol l–1). The retention times for VV and VIV were 4.91 and 9.01 min, respectively. The calibration graphs obtained for 100 µl samples were linear for 0.02–2.00 µg ml–1 vanadium. The detection limits were 0.2 and 0.1 ng per 100 µl sample volume for VV and VIV, respectively. The proposed method for the simultaneous speciation of vanadate and vanadyl ions was used to analyse a used vanadium-containing catalyst and good results were obtained in terms of precision and accuracy.