Simple microplate method for determination of urinary iodine

Abstract

Background: Urinary iodine is a good biochemical marker for control of iodine deficiency disorders. Our aim was to develop and validate a simple, rapid, and quantitative method based on the Sandell-Kolthoff reaction, incorporating both the reaction and the digestion process into a microplate format.

Methods: Using a specially designed sealing cassette to prevent loss of vapor and cross-contamination among wells, ammonium persulfate digestion was performed in a microplate in an oven at 110 degrees C for 60 min. After the digestion mixture was transferred to a transparent microplate and the Sandell-Kolthoff reaction was performed at 25 degrees C for 30 min, urinary iodine was measured by a microplate reader at 405 nm.

Results: The mean recovery of iodine added to urine was 98% (range, 89-109%). The theoretical detection limit, defined as 2 SD from the zero calibrator, was 0.11 micromol/L (14 microg/L iodine). The mean intra- and interassay CVs for samples with iodine concentrations of 0.30-3.15 micromol/L were < or = 10%. The new method agreed well with the conventional chloric acid digestion method (n = 70; r = 0.991; y = 0.944x + 0.04; S(y|x) = 0.10) and with the inductively coupled plasma mass spectrometry method (n = 61; r = 0.979; y = 0.962x + 0.03; S(y|x) = 0.20). The agreement was confirmed by difference plots. The distributions of iodine concentrations for samples from endemic areas of iodine deficiency diseases showed similar patterns among the above three methods.

Conclusions: Our new method, incorporating the whole process into a microplate format, is readily applicable and allows rapid monitoring of urinary iodine.