Spectrophotometric determination of iodine species in table salt and pharmaceutical preparations

A sensitive spectrophotometric method for the determination of iodine species like iodide, iodine, iodate and periodate is described. The method involves the oxidation of iodide to ICl-2 in the presence of iodate and chloride in acidic medium. The formed ICl-2 bleaches the dye methyl red. The decrease in the intensity of the colour of the dye is measured at 520 nm. Beer's law is obeyed in the concentration range 0-3.5 μg of iodide in an overall volume of 10 ml. The molar absorptivity of the colour system is 1.73×105lmol-1cm-1 with a correlation coefficient of -0.9997. The relative standard deviation is 3.6% (n=10) at 2 μg of iodide. The developed method can be applied to samples containing iodine, iodate and periodate by prereduction to iodide using Zn/H+ or NH2NH2/H+. The effect of interfering ions on the determination is described. The proposed method has been successfully applied for the determination of iodide and iodate in salt samples and iodine in pharmaceutical preparations. © 2008 Pharmaceutical Society of Japan.