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 °C for 60 min. After the digestion mixture was transferred to a transparent microplate and the Sandell–Kolthoff reaction was performed at 25 °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 μmol/L (14 μg/L iodine). The mean intra- and interassay CVs for samples with iodine concentrations of 0.30–3.15 μmol/L were ≤10%. The new method agreed well with the conventional chloric acid digestion method (n = 70; r = 0.991; y = 0.944x + 0.04; Sy|x = 0.10) and with the inductively coupled plasma mass spectrometry method (n = 61; r = 0.979; y = 0.962x + 0.03; Sy|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.

Iodine deficiency among pregnant women living in Northern Ireland

“…Height Urinary iodine concentration was measured using a multiplate persulphate digestion method followed by Sandell-Kolthoff colorimetry and expressed as μg/L as previously described. 2,15 Samples were analysed in triplicate for iodine, and the limit of detection was 10 μg/L. The laboratory participated in the Ensuring the Quality of Urinary Iodine Procedures (EQUIP) programme at the US Centers for Disease Control and Prevention (CDC Atlanta, Georgia, USA).…”

Validation of a short food frequency questionnaire specific for iodine in UK females of childbearing age

“…The urine collections were kept in an opaque container placed in a cool-bag, aliquoted and stored at À80°C until analysis. Urinary iodine was measured using a microplate adaptation of the Sandell-Kolthoff colorimetric method (Ohashi et al, 2000). The percentage coefficient of variation of the assay was 2% at 125 lg L À1 , 2% at 62.5 lg L À1 and 19% at 15.5 lg L À1 .…”

Persistent iodine deficiency in a cohort of Tasmanian school children: associations with socio-economic status, geographical location and dietary factors

“…Samples were stored in the dark at 4°C for a maximum of four weeks before assay. The laborator y analyses were performed by the Institute of Clinical P athology and Medical Research (ICPMR), Laboratory Endocrinology Department at Westmead Hospital in Sydne y, using the Ohashi mircroplate method, 20 based on the Sandel-Kolthoff reaction.…”