Kinetic spectrophotometric determination of vanadium by catalytic effect on the indigo carmine-bromate reaction

A sensitive kinetic method for determination of vanadium is reported at pH 2 and 25 degrees C. The catalytic effect of vanadium on the oxidation of indigo carmine by bromate goes through an induction period and then decreases in absorbance at 612 nm, which is the maximum absorption wavelength of indigo carmine. Both the induction period and slope methods were applied for determination of vanadium. Concentration ranges of 0.3-30 (mu g.mL(-1)) of vanadium were determined. The limit of detection was found to be 0.27 (mu g.mL(-1)). Six replicate analysis of a sample solution containing 10 mu g.mL(-1) vanadium gave a relative standard deviation of 1.3%. The interference effects of various cations and anions on vanadium determination is reported, and the interference of ions are eliminated by a simple procedure. Application of the method to real samples such as crude petroleum are performed which gave acceptable results.