A CATALYTIC METHOD FOR THE DETERMINATION OF TRACE VANADIUM IN SALT SAMPLES

A simple and sensitive catalytic method for the determination of vanad ium in salt samples was developed by using the vanadium-catalyzed oxid ation of leucomethylene blue to methylene blue with bromate at pH 4.6 and 20 degrees C. The absorbance (A) of methylene blue was monitored a t 667 nm for 1 min of reaction time (t). The calibration graph of vana dium was constructed by using the reaction rate, i.e. the slope of the A versus t graph. The addition of pure sodium chloride to reference s olutions compensated the matrix effect and effectively eliminated the chemical interferences. The same calibration graph with a linear range of 0 to 7 mu g l(-1) was obtained for both V(IV) and V(V). The detect ion limit was 0.2 mu g l(-1) (1 ng). The proposed method was successfu lly applied to the determination of vanadium down to 3 ng g(-1) in 0.2 to 0.3 g of ordinary and sun-dried salts.