Quantifying salivary iodine biomarker using total reflection X-ray fluorescence (TXRF): A method for assessing and monitoring iodine status simulated by Monte Carlo

Abstract

Iodine stands as a vital trace element essential crucial for synthesizing thyroid hormones, which are essential for regulating metabolism and tissue growth. The “gold standard” for assessing iodine status in a population quantifies the iodine content in urine samples and is based on Inductively Coupled Plasma - Mass Spectrometry (ICP-MS). Such method, or methods involving the readings of the Sandell-Kolthoff (SK) reaction, require complex sample preparations and the use of several toxic chemical elements. However, recent studies have shown a strong correlation between urinary iodine content (UIC) and iodine present in saliva. Using Monte Carlo simulations, this paper presents a TXRF-based method to quantify salivary iodine biomarker for assessing and monitoring iodine status. In the theoretical analysis, mono and polychromatic (filtered) excitation sources are considered. The detection and quantification limits of iodine, as well as the calibration curves for mass recovery, used the strong I Kα1 and I Kα2 lines. It was found that the optimal X-ray excitation source energy for iodine detection is 50 keV monochromatic X-rays. In contrast, using simulated spectra from a tungsten anode target, the best result was found at 70 kVp (peak voltage), after filtering the white beam with a copper absorber. Detection limits of iodine are 0.121 ng and 2.292 ng, for mono and polychromatic sources, respectively. The theoretical results of this paper show that TXRF could be a fast, simple and accurate alternative to ICP-MS or SK reaction-based methods. Of clinical significance, quantifying salivary iodine using TXRF to assess and monitor iodine status could be particularly helpful to patients undertaking 131I treatment. In addition, it could be used in epidemiological field studies to determine iodine deficiency/excess in children and pregnant women.