Colour reaction of Iodate with 3,3′,5,5′Tetramethylbenzidine and Its Analytical Application

A new spectrophotometric method for the determination of trace iodate was developed, based on the reaction of iodate with 3,3′,5,5′ tetramethylbenzidine(TMB).In the medium of HCl, when TMB is oxidized by iodate, a yellow imine is formed and gives a strong absorption at 450 nm ,its apparent molar absorptivity is 2.13×10 5 L·mol -1 ·cm -1 . Beer's law is obeyed in the range of 0～0.7mg/L for iodine. The method was applied to the determination of trace iodine in salt with potassium iodate added with satisfactory results.