KINETIC DETERMINATION OF VANADIUM USING THE BROMATE OXIDATIVE COUPLING REACTION OF 4-(METHYLAMINO)PHENOL WITH 2,3,4-TRIHYDROXYBENZOIC ACID AND TARTRATE ACTIVATOR

ABSTRACT A new, simple, sensitive and selective kinetic method is developed for the spectrophotometric determination of VV and/or VIV based on its catalytic effect on the bromate oxidative coupling reaction of 4-(methylamino)phenol (MAP) with 2,3,4-trihydroxybenzoic acid (THBA) in the presence of tartrate as an activator. The reagents: 6.4 mmol l−1 MAP, 2.0 mmol l−1 THBA and 160 mmol l−1 bromate were mixed in the presence of an activator-buffer solution of 10 mmol l−1 tartrate (pH = 3.10) and at 35°C. The rate of formation of the oxidative coupling product was followed at 380 and/or 570 nm for 3 min from the addition of bromate. Linear calibration graphs up to 0.75 ng ml−1 of vanadium were obtained with detection limits, based on the 3S b criterion, of 0.019 and 0.026 ng ml−1 at 380 and 570 nm, respectively. The developed method was conveniently applied to the determination of vanadium in tap and ground waters and in human plasma, serum, and urine. Moreover, the nature of the oxidative coupling product was inferred and the kinetics and mechanism of the activating effects of tartrate were elucidated.