Analytical Sciences

Catalytic Spectrophotometric Determination of Vanadium in Seawaters Based on the Bromate Oxidative Coupling Reaction of Metol and 2,3,4-Trihydroxybenzoic Acid

Ashraf A. MOHAMED  and Khalid F. FAWY

Department of Chemistry, Faculty of Science, Ain Shams University, Abbassia, Cairo-11566, Egypt

A new, simple, sensitive and selective catalytic method is developed for the determination of vanadium in natural and sea waters. The method is based on the catalytic effect of V^V and/or V^IV on the bromate oxidative-coupling reaction of metol with 2,3,4-trihydroxybenzoic acid (THBA). The reaction is followed spectrophotometrically by tracing the oxidation product at 380 and/or 570 nm after 5 min of mixing the reagents. The optimum reaction conditions are 6.4 x 10^-3 mol l^-1 of metol, 2.0 x 10^-3 mol l^-1 of THBA and 0.16 mol l^-1 of bromate at 35°C and in the presence of an activator-buffer solution of 1 x 10^-2 mol l^-1 of tartrate (pH = 3.10). Following the recommended procedure, V^V and/or V^IV can be determined with linear calibration graphs up to 0.75 ng ml^-1 and detection limits, based on the 3Sb criterion, of 0.008 and 0.018 ng ml^-1 at 380 and 570 nm, respectively. The developed method was successfully applied, without any separation or preconcentration processes, to the determination of vanadium in natural and seawaters following the direct calibration and standard addition techniques, respectively.

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