New Methods For Trace Analysis Of Iodine And Perchlorate In Biological Fluids

Abstract

Iodine is an essential element necessary for the production of the thyroid hormones T3 and T4. These hormones are necessary for metabolism and are especially important for brain development in infants and young children. Iodine is transported into the thyroid by the sodium iodide symporter. Perchlorate is known to inhibit iodine uptake into the thyroid by binding to the sodium iodide symporter, thus acting as a potential neurotoxicant for developing children.The research in this dissertation consists of two goals. The primary is the development of novel methods for measuring iodine and perchlorate and the second is performing analyses to determine infant risk associated with perchlorate consumption via milk. Further research performed not relevant to the title theme is included in the appendices. The iodine status of infants is not well known. Urinary iodine is used as the primary epidemiological marker for gauging the iodine status of an adult population. Infant risk assessment however, due to difficulties acquiring infant urine samples, is more frequently monitored via the feed, e.g. milk. Measurement of iodine and perchlorate in milk is no simple task. Complete sample digestion is preferred for iodinalysis, but the harsh conditions often rule out such methods to be used for perchlorate analysis. Iodide present in the milk may also be oxidized to molecular iodine which is volatile and may be lost prior to analysis. We have developed a new digestion procedure for the removal of organics based on the Fenton reaction: the Fe2+ catalyzed oxidation of organics by H2O2. The method is green, safe, inexpensive and effective. Iodine loss is kept to a minimum by controlling the temperature and pH of the reaction. Additionally, the reaction is mild enough such that perchlorate remains intact throughout the digestion.The digestion procedure was used for the analysis of breast milk samples and corresponding infant urinary secretions. Using iodine as a conservative tracer in the infants, it is found that perchlorate is actually reduced in breastfed infants as opposed to their formula fed counterparts. One of the primary physiological differences between breastfed and formula fed infants is intestinal bacteria. Milk spiked with perchlorate was inoculated with bifidobacteria, the dominant intestinal bacteria in breastfed infants. Perchlorate reduction occurred in those samples with bifidobacteria compared to those with a bacteria blend that didn't contain it.Currently there is no means of measuring an individual's iodine nutrition status. An inexpensive device was developed capable of measuring iodine to levels necessary for identifying severe deficiency. The system was based on a gas-phase preconcentration microplasma dielectric barrier discharge atomic emission spectrometer. Iodine is absorbed on a suitably coated tungsten filament of low thermal mass. The filament is heated rapidly and the iodine is vaporized and measured in the plasma. The biggest obstacle to final development of a working unit is the chemistry of iodine itself. Oxidation of I- to I2 and removal from solution is a seemingly easy task given that I- is readily oxidized and I2 is volatile with low solubility in water. However, disproportionation reactions are prevalent at low iodine concentrations and necessitate the need for alternative approaches such as generation of CH3I.