A Robust Method for Iodine Status Determination in Epidemiological Studies by
Capillary Electrophoresis
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Abstract
Iodine
deficiency is the most common preventable cause of intellectual
disabilities in children. Global health initiatives to ensure optimum
nutrition thus require continuous monitoring of population-wide iodine
intake as determined by urinary excretion of iodide. Current methods
to analyze urinary iodide are limited by complicated sample pretreatment,
costly infrastructure, and/or poor selectivity, posing restrictions
to large-scale epidemiological studies. We describe a simple yet selective
method to analyze iodide in volume-restricted human urine specimens
stored in biorepositories by capillary electrophoresis (CE) with UV
detection. Excellent selectivity is achieved when using an acidic
background electrolyte in conjunction with dynamic complexation via
α-cyclodextrin in an unmodified fused-silica capillary under
reversed polarity. Sample self-stacking is developed as a novel online
sample preconcentration method to boost sensitivity with submicromolar
detection limits for iodide (S/N ≈ 3, 0.06 μM) directly
in urine. This assay also allows for simultaneous analysis of environmental
iodide uptake inhibitors, including thiocyanate and nitrate. Rigorous
method validation confirmed good linearity (<i>R</i><sup>2</sup> = 0.9998), dynamic range (0.20 to 4.0 μM), accuracy
(average recovery of 93% at three concentration levels) and precision
for reliable iodide determination in pooled urine specimens over 29
days of analysis (RSD = 11%, <i>n</i> = 87)