Catalytic spectrophotometric determination of bromide based on the diphenylcarbazide-chromium(VI)-iodate reaction

A new catalytic spectrophotometric method for the determination of bromide is proposed. Diphenylcarbazide reacts with chromium(VI) ions in an acid medium to give a violet complex. The method is based on the bromide-catalyzed oxidation of this violet complex by iodate followed by measuring the color change at lambda = 542 nm spectrophotometrically. The reaction starts after an induction period. Bromide ions catalyze this reaction, so that the induction period is decreased by the addition of Br-. The derivative of the absorbance with respect to time was calculated. The maximum absorbance difference (DeltaA(m)) and thetime taken to reach the maximum difference (t(m)) were measured from the derivative curve. These values are used as the measured parameters for bromide determination. Under optimum conditions bromide can be determined in the range of 0.5-8 mug/mL. The detection limit is 0.25 mug/mL, and the relative standard deviation for ten replicate measurements of 1 mug/mL of bromide is 1.57%. The method was applied to the determination of bromide in the Persian Gulf water.