Determination of total iodine and iodate in sea water and in various evaporites

Iodine in sea water and evaporites is determined spectrophotometrically as the starch-iodine complex without prior separation or concentration of the iodine. In slightly alkaline solution, iodide is first oxidized to iodate with permanganate. Oxidized states of manganese are destroyed with iron(II) in phosphate medium without affecting the iodate. After acidification, iodide is added to react with the iodate in the presence of starch. The iodate content is determined by the same procedure, but without the addition of permanganate. As little as 0.1μg of iodine is determinable in the presence of 500 mg of chloride and 5 mg of bromide. The total iodine concentration in seven samples of sea water was found to vary from 50 ±3 to 84 ±6 μg l^-1 with 50–100% present as the iodate.