Determination of urinary iodine by inductively coupled plasma mass spectrometry

Abstract

Background: Mild iodine deficiency is endemic in many countries of Europe including Belgium. Fast, accurate and specific methods for quantification of urinary iodine are needed. We describe in this report a specific ICP-MS method for the quantification of urinary iodine.

Method: Samples and iodate calibrators were diluted 20 times into aqueous solution containing triton X-100, 1.5% HCl and (103)Rh as an internal standard. Prior digestion or oxidation was not necessary. Results were compared with those obtained by Sandell-Kolthoff (S-K) spectrophotometric method.

Results: Comparison of both methods showed good agreement. The Passing-Bablok regression between both methods was ICP-MS=0.986 (S-K)-7.51. The Bland-Altman difference plot showed a small but significant mean difference of -13.3 microg/L for ICP-MS. The between-day coefficient of variation (CV) was 13% at 89 microg/L. Limit of detection was 4 microg/L and limit of quantification was 20 microg/L. No carryover effect has been observed on series containing up to 50 samples.

Conclusion: The ICP-MS method described here is fast, accurate and specific for the quantification of urinary iodine. Compared to the S-K method the urinary iodine concentrations measured by the ICP-MS method were slightly, but significantly lower. Consequently, the results of studies using S-K method should be compared with caution with those using the ICP-MS method.