Method for biochemical monitoring of iodine. Determination of iodide-ion in urine with an ion-selective electrode

Determination of iodine in urine is an important methodology in the assessment of thyroid disorders. This indicator is often used in epidemiological studies of the state of iodine nutrition of the population, since the widespread prevalence of human iodine deficiency diseases is directly related to the lack of iodine intake with food and water. A method for the iodide ion determination in urine has been developed based on preliminary preservation of the sample in the presence of a buffer solution containing 4.28 %wt. H₂O₂ at pH 6.8 – 7.5 and measurements of the potential of the iodide selective electrode directly in the preserved sample solution without separation of the interfering components. After mixing the sample with a buffer solution in a ratio of 1:1, it is preserved after 18 – 24 h and stored for at least 30 days. The interfering effect of macro- and micro-components has been studied. It is shown that the amount of sodium chloride in the sample should be taken into account only in studying the severe iodine deficiency (≤20 μg/liter) and urea does not affect the potential of the electrode. To assess the total effect of the organic components of urine, we compared the results of parallel determinations of iodine in the samples, one of which was preserved, and organics was removed from the second one by alkaline ashing. It is shown that the discrepancies in the results were random and did not exceed 11.3 %. Iodine loss has not been determined, the bias between the concentration of the introduced and found additives was insignificant. Thus, in a buffer solution with hydrogen peroxide, not only the preservation of the urine sample for a long time takes place, but also the interfering influence of inorganic and organic components of the sample matrix on the membrane of the ion-selective electrode is eliminated. Metrological evaluation of the developed methodology was performed, which showed the precision and trueness of the procedure. The method was tested in an experiment on the correction and enrichment of iodine in the diet of schoolchildren. The low cost, convenient and easy to use equipment, the possibility of long-term storage of preserved samples makes the method mobile and suitable for biochemical monitoring of iodine consumption and deficiency during a large-scale population survey.

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