Highly selective and sensitive kinetic spectrophotometric determination of vanadium(IV) in the presence of vanadium(V)

A highly selective and sensitive method is presented for the determination of V(IV), based on its catalytic effect on the oxidation reaction of aniline blue by bromate. The reaction was monitored spectrophotometrically by measuring the decrease in absorbance of aniline blue at 591 nm, between 0.5 to 5 min (the fixed time method). The effect of various parameters such as pH, concentrations of bromate and aniline blue, temperature and ionic strength on the rate of reaction were studied. The method is free from most interferences, especially from large amounts of V(V). The decrease of absorbance is proportional to the concentration of V(IV) over the entire concentration range tested (5-1200 ng ml(-1)) with a 3 sigma detection limit of 2.0 ng ml(-1) and a relative standard deviation at 60-200 ng ml(-1) V(IV) of ca. 3% (n = 3). The method was applied to the determination of V(IV) in river water and some synthetic samples with satisfactory results. (C) 2000 Elsevier Science B.V. All rights reserved.