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 med ium 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 indu ction period is decreased by the addition of Br-. The derivative of the abs orbance with respect to time was calculated. The maximum absorbance differe nce (DeltaA(m)) and thetime taken to reach the maximum difference (t(m)) we re measured from the derivative curve. These values are used as the measure d parameters for bromide determination. Under optimum conditions bromide ca n be determined in the range of 0.5-8 mug/mL. The detection limit is 0.25 m ug/mL, and the relative standard deviation for ten replicate measurements o f 1 mug/mL of bromide is 1.57%. The method was applied to the determination of bromide in the Persian Gulf water.