STUDY ON THE INHIBITION OF OXIDATION-DECOLORATION REACTION BETWEEN 5-Cl-PADAT AND H2O2 BY VANADIUM(Ⅴ) AND ITS APPLICATION TO PHOTOMETRIC DETERMINATION OF VANADIUM

In a citrate buffer of pH 1.7 and heated for 10 min in boiling water bath,the oxidative color-fading of 5-Cl-PADAT by H2O2 was inhibited by traces of vanadium(Ⅴ).Difference of absorbance (ΔA) of solutions in the presence of V(Ⅴ) (A) and in the absence of V(Ⅴ) (A0) measured at λmax 460 nm kept a linear relationship with the concentration of vanadium(Ⅴ) in the range of 0-91.8 ng per 25 mL of solution.Its detection limit was found to be 7.19×10-9g·L-1.Most of the common co-existing ions did not interfere the determination.Kinetic parameters of the oxidation reaction were also studied.It was concluded on the results of graphical integration that both the reaction with V(Ⅴ) and H2O2 or with H2O2 only,were of zero order.The apparent activity energy were found to be 61.6 kJ·mol-1 and 82.1 kJ·mol-1 for reactions of R+H2O2 and R+H2O2+V(Ⅴ) respectively.The optimum temperature of heating for the reaction was 100 ℃.RSD′s in the range from 1.8% to 2.6% and recoveries in the range from 98.1% to 105.0%,were found in the analysis of blood and tea samples.