Determination of micro amounts of iodide ion by the catalytic reaction

A new catalytic reaction of iodide ion was applied to the spectrophotometric determination of micro amounts of iodine with Pyrocatechol Violet as the reagent. Pyrocatechol Violet was discolored by hydrogen peroxide in dilute HCl-HNO3 solution, and this reaction was greatly enhanced by the catalytic action of trace iodide. Iodine in the range of 0.010.1 ppm was determined successfully by measuring absorbances at 550 mμ after an hour. As much as 10 times of Fe(II) and (III), Cu(II) and Zn(II), and 1000 times of Al(III), Ba(II), Co(II), Cl-, ClO3-, Ca(II), F-, SO42-, H2PO4-, Li(I), Mg(II), Pb(II) and Sr(II) scarcely interfered. Br- and ClO4- interfered seriously.