Iodine Quantification in Human Saliva by Inductively Coupled Plasma Mass Spectrometry: A Preliminary Cohort Study

Abstract

A method for the direct determination of iodine in saliva samples using inductively coupled plasma-mass spectrometry (ICP-MS) without the need of sample digestion was designed and tested. Simple sample dilution with 1% (v/v) aqueous ammonia adding 130Te (20 μg/L) as internal standard was shown to provide reliable and accurate results. Saliva sample storage stability was checked across different measurement days and after an additional freeze-thaw cycle. The data was validated using spike recoveries and certified reference material analysis (recoveries of 96-103%). The method designed provided limit of detection of iodine in saliva of 2.9 μg/L and average inter-day relative standard deviation (RSD) of 9-11%. A small cohort study (n = 20) was conducted among the adult volunteers from an iodine-sufficient-to-mildly deficient region in the Northwest of Ireland. The samples were collected using unstimulated spittle technique after fasting for at least 2 hours. The study demonstrated log-normal distribution of salivary iodine concentration with the values (median 122 µg/L, interquartile range of 108 µg/L), exhibiting trends consistent with previously reported in the literature. Although the results indicated that salivary iodine might serve as a practical surrogate for urinary iodine, further large-scale studies are warranted to refine and compare salivary iodine with other established biomarkers to confirm its diagnostic utility in epidemiological and clinical settings.