Effect of tartrate on vanadium-catalysed chlorpromazine–bromate redox reaction and its application to the determination of vanadium in natural waters

Abstract

The spectrophotometric determination of vanadium using the catalytic oxidation of chlorpromazine (CPH) with bromate was sensitized in the presence of sodium tartrate (TART) as an activator. The red oxidation product of CPH was monitored at 525 nm within a 1 min reaction time. Vanadium was determined by the measurement of its oxidation rate. The detection limit was 0.2 ng cm^–3 using optimized reaction conditions of 5 × 10^–4 mol dm^–3 CPH, 5 × 10^–3 mol dm^–3 KBrO₃, 0.1 mol dm^–3 TART and 0.35 or 0.5 mol dm^–3 H₃PO₄ at 25 °C. The calibration graph was linear up to 150 ng cm^–3 V^V or V^IV. The interferences from Br^–, I^–, S^2– and NO₂^– were eliminated by the addition of Ag^I and methanol. The proposed method was successfully applied to the determination of vanadium in rain and river waters.