Chapter 15 - Iodine Speciation in Foodstuffs, Tissues, and Environmental Samples: Iodine Species and Analytical Method

Abstract

This chapter presents the analytical methods for iodine species in water, air, tissues and biological samples, and also in foodstuffs and environmental samples. Different species of iodine are involved in the transport of iodine from air, soil and water to food, and from food to the human body. In water, most iodine occurs as iodide and iodate while, in some cases, the concentration of organic iodine may be high. In the air, iodine exists as particle associated iodine, inorganic gaseous iodine (I2, HIO), and organic gaseous iodine (CH3I, CH2I2, etc.). In the body of humans and other mammals, iodine is utilized by the thyroid gland for the biosynthesis of the thyroid hormones T÷ and T×. Besides T× and T÷, iodine also exists as MIT, DIT, T3, and rT3, which are mainly bound with proteins in thyroid and other tissues, but function as free T3 and T4. In milk and urine, most iodine occurs as iodide, but some species of organic iodine were also found. The most commonly used methods for speciation analysis of iodine in tissues and food are chromatographic techniques, such as anion exchange, size exclusion and reverse-phase chromatography, coupled with inductively coupled plasma mass spectrometry (ICP-MS) detection. Iodide and iodate have a low toxicity and high bioavailability, whereas the toxicity of elemental iodine and periodate is high. The bioavailability of organic iodine, especially iodine associated with macromolecules, is low.