A new kinetic method has been developed for the determination of iodine in water samples. The method is based on the catalytic effect of I− with the oxidation of Indigo Carmine (IC) by KBrO3 in the sulfuric acid medium. The optimum conditions obtained are 0.16 M sulfuric acid, 1×10−3 M of IC, 1×10−2 M KBrO3, reaction temperature of 35°C, and reaction time of 80 s at 612 nm. Under the optimized conditions, the method allowed the quantification of I− in a range of 12–375 ng/mL with a detection limit of 0.46 ng/mL. The method was applied to the determination of iodine in river and city water samples with the satisfactorily results.
