Catalytic spectrophotometric determination of vanadium in seawaters based on the bromate oxidative coupling reaction of metol and 2,3,4-trihydroxybenzoic acid

A new, simple, sensitive and selective catalytic method is developed for th e 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-couplin g 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 cond itions 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 degreesC and in the presence of an acti vator-buffer solution of 1 x 10(-2) mol l(-1) of tartrate (pH = 3.10). Foll owing the recommended procedure, V-V and/or V-IV can be determined with lin ear calibration graphs up to 0.75 ng ml(-1) and detection limits, based on the 3S(b) criterion, of 0.008 and 0.018 ng ml(-1) at 380 and 570 nm, respec tively. The developed method was successfully applied, without any separati on or preconcentration processes, to the determination of vanadium in natur al and seawaters following the direct calibration and standard addition tec hniques, respectively.