On-line preconcentration and sample clean-up system for the determination of vanadium as a 4-(2-pyridylazo) resorcinol–hydrogen peroxide ternary complex in plant tissues by ion-interaction high performance liquid chromatography

Abstract

An HPLC method for the determination of vanadium using on-line preconcentration and sample clean-up has been developed employing a C 18 column. 4-(2-Pyridylazo) resorcinol (PAR) and hydrogen peroxide were used as pre-column complexing agents for the determination of vanadium. Aliquots of either standard or sample solutions (100 μL and 2 mL) containing the vanadium complex were loaded onto a guard column (C 18, 0.4 mm × 4.6 mm) with a carrier mobile phase comprising 20% (v/v) methanol, 5 mM acetic acid, 5 mM citric acid, l0 mM tetrabutylammonium bromide (TBABr) at pH 7 (eluent 1). A flow rate of 2 mL/min for 0.40 min was used for a 100 μL injection loop, and 1.65 min for the 2 mL injection loop, with the effluent being directed to waste. The vanadium complex was flushed onto the analytical column (C 18, 150 mm × 3.9 mm, 4 μm), via an automatic switching valve, using a mobile phase comprising 32% (v/v) methanol, 5 mM acetic acid, 5 mM citric acid, and 5 mM tetrabutylammonium bromide (TBABr) at pH 7, with a flow rate of 1 mL/min for 1.60 min. The switching valve was returned to its original position, and any unwanted species remaining on the guard column were eluted with methanol for 5 min. The guard column was then re-equilibrated with eluent 1 for 5 min before the next injection. The analytes were detected at 540 nm. The detection limits (determined by a signal-to-noise ratio of 3) of vanadium with on-line preconcentration using 2 mL and 100 μL injection loops were 3.1 and 67 ng/kg, respectively. The developed method was used for the determination of vanadium in plant tissue. Chinese green mustard and tomato plant samples analysed in this study were cultured hydroponically. Vanadium concentrations measured using the HPLC technique were compared with those obtained using magnetic sector ICP-MS. Vanadium levels in plant tissue samples (root, stem and leaf of Chinese green mustard) found by HPLC agreed well (>85%) with those found using magnetic sector ICP-MS.