Analytical validation of an inductively coupled plasma mass spectrometry method for urinary iodine concentration measurements in Taiwan

Background: Urinary iodine concentration (UIC) measured by Sandell-Kolthoff spectrophotometric method has been used in the Nutrition and Health Surveys in Taiwan but this method is time consuming and produces toxic waste from arsenic trioxide. The aim of this study was to develop and validate an inductively coupled plasma mass spectrometry (ICP-MS) system to determine UIC in Taiwan. Methods: Samples and iodine calibrators were diluted 100-fold into an aqueous solution containing Triton X-100, 0.5% ammonia solution, and tellurium (¹²⁸Te) as an internal standard. Digestion prior to analysis was not necessary. Precision, accuracy, serial dilution, and recovery tests were performed. A total of 1243 urine samples covering a wide range of iodine concentrations were measured by both Sandell-Kolthoff method and ICP-MS. Passing-Bablok regression and Bland–Altman plots were used to compare values across methods. Results: The limit for detection and quantification by ICP-MS was 0.95 μg/L and 2.85 μg/L, respectively. The intra-assay and inter-assay coefficients were <10%, with a recovery range of 95%–105%. The results obtained by ICP-MS and the Sandell-Kolthoff method were highly correlated (Pearson's correlation: r = 0.996, 95% confidence interval [CI]: 0.9950–0.9961, p < 0.001). For UIC between 20 and 1000 μg/L, the y-intercept for the Passing-Bablok regression was −1.9 (95% CI: −2.5599 to −1.3500) and the slope was 1.01 (95% CI: 1.0000–1.0206). Conclusion: This validated ICP-MS system can be used for measuring UIC.