Simultaneous determination of vanadium(IV) and vanadium(V) as EDTA complexes by capillary zone electrophoresis

Abstract

A capillary zone electrophoretic method with on-column UV detection for the simultaneous determination of aqueous vanadium(IV) and vanadium(V) ions was studied. Vanadium(IV) and vanadium(V) were chelated with ethylenediaminetetraacetic acid (EDTA) to form anionic V(IV)-EDTA and V(V)-EDTA complexes prior to the analysis. A fused-silica capillary column (100 cm × 75 m i.d.) modified with hexadecyltrimethylammonium bromide was used to separate the V(IV)-EDTA and V(V)-EDTA complexes. A 50 mmol sodium acetate buffer (pH 4.6) containing 0.5 mmol EDTA was used as the electrolyte. Separation was performed at an applied voltage of −18 kV. The separated vanadium species were monitored spectrophotometrically at 280 nm. The electrophoretic behavior of vanadium species was examined in detail. Factors that affect the separation of vanadium species, such as running buffer pH, electrolyte concentration, detection wavelength, EDTA concentration, as well as applied voltage, were systematically optimized. Calibration graphs were linear over two orders of magnitude with detection limits of 0.1 μg ml −1 (V(V)) and 0.4 μg ml −1 (V(IV)). The method was applied to the analysis of a catalyst-leachate sample.