Catalytic determination of vanadium based on the bromate oxidative-coupling reaction of metol with phloroglucinol

A selective, sensitive and simple catalytic method is developed for the det ermination of vanadium in natural and highly polluted waste waters. The met hod is based on the catalytic effect of V-V and/or V-IV on the bromate oxid ative-coupling reaction of metol with phloroglucinol (PG). The reaction is followed spectrophotometrically by tracing the oxidation product at 464 nm after 10 minutes of mixing the reagents. The optimum reaction conditions ar e metol (8.0 x 10(-3) M), PG (4.0 x 10(-3) M) and bromate (2 x 10(-2) M) at 35 degrees C and in presence of an activator-buffer mixture of 5 x 10(-2) M of each of citric and monochloroacetic acids (pH 2.40). Following the rec ommended procedure, vanadium can be determined with a linear calibration gr aph up to 8.0 ng mL(-1) and a detection limit, based on the 3s(b) criterion , of 0.1 ng mL(-1). Spectrophotometric determination of as little as 1.0 ng mL(-1) of V-V or V-IV in aqueous solutions gave an average recovery of 98% with relative standard deviations of less than or equal to 1.8% (n = 5). T he proposed method was directly applied to the determination of vanadium in Nile river water and highly polluted industrial wastes. Statistical treatm ents of analytical results could not detect any systematic error and showed the high accuracy and precision of the developed method.