Determination of iodide and iodate in aqueous solution



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Sufficient daily dietary iodine (I2) intake is necessary for the production of thyroid hormones. Insufficient iodine intake or assimilation impairs the synthesis of thyroid hormones and may result in hypothyroidism. If hypothyroidism occurs early in life, a range of functional and physiological abnormalities collectively termed “Iodine Deficiency Disorders” (IDD) may develop. Iodate and Iodide are the only two forms in which iodine is added to table salt. Iodide is used in the US but iodization has never been mandatory and iodine content of table salt has never been determined independently. Potassium iodide (KI) added to table salt may oxidize and then sublime at ambient humidity and temperature. Further additives are sometimes added to salt, including silica or calcium silicate (to maintain free flowing characteristics) and dextrose or sodium thiosulfate (as an iodine preservative). We have collected table salt supplied by volunteers from across the US. The iodine content of the salt samples was measured by ICP-MS with Ge as an internal standard. The determination of iodate is of great interest for the studies of an iodized salt program in Asian countries because iodate is the iodization vector for salt in Asia. Iodate is also naturally formed and the content of iodate in natural deposits is of interest. We describe an electrochemical detection system in which aqueous iodate is reduced on a stainless steel working electrode with a platinum auxiliary electrode in acidic medium. Under optimized applied voltage, the electrochemical reduction current peak height is directly related to iodate concentration in the samples. This method has been successfully applied to determine iodate concentration in five Chilean Caliche samples and eight table salt samples obtained from India, China, Thailand and Australia.