Catalytic-kinetic spectrophotometric determination of vanadium (V) based on the Celestine blue-bromate-vanadium (V)-citric acid reaction

摘要

A novel sensitive and relatively selective kinetic method is presented for the determination of V(V) based on its catalytic effect on the oxidation reaction of Celestine blue by potassium bromate in the presence of citric acid as an activator.The reaction was monitored spectrophotometrically by measuring the decrease in absorbance of Celestine blue at a maximum absorption wavelength of 540 nm between 0.5 and 9 min(the fixed-time method) in an H3PO4 medium at 45°C.The effect of various parameters such as concentrations of H3PO4,citric acid,potassium bromate and Celestine blue,ionic strength,reaction temperature and time on the rate of V(V) catalyzed reaction was studied.The method is free from the most interferences,especially from large amounts of V(IV).The decrease in absorbance is proportional to the concentration of V(V) over the entire concentration range tested(0.025-1.25 μg·mL-1) with a detection limit of 6.80 μg·L-1(according to statistical 3Sblank/k criterion) and a coefficient of variation(CV) of 1.78%(for ten replicate measurements at 95% confidence level).The proposed method suffers from a few interferences such as Cr(VI) and Hg(II) ions.The method was successfully applied to the determination of V(V) in river water,lake water,tap water,natural drinking water samples and a certified standard reference material such as SRM-1640 with satisfactory results.The vanadium contents of natural water samples were detected by using both linear calibration curve and standard addition curve methods.The recoveries of spiked vanadium(V) into the certified standard water sample were found to be quantitative,and the reproducibility was satisfactory.It was observed that the results of the SRM 1640 were in good agreement with the certified value.