Validation of a Capillary Electrophoresis Assay for Monitoring Iodine Nutrition in Populations for Prevention of Iodine Deficiency: An Interlaboratory Method Comparison

Abstract

Background: A capillary electrophoresis (CE) assay was recently introduced as a new method for monitoring iodine nutrition in large-scale epidemiological studies. However, further tests revealed unanticipated matrix-dependent interferences when analyzing submicromolar levels of iodide in human urine as the predominate ionic form of dietary iodine. Herein, we describe a rigorous validation study that was used to identify sources of bias and establish modifications to the original CE method to improve method accuracy. Methods: An interlaboratory method comparison using CE with UV detection and inductively coupled plasma-mass spectrometry (ICP-MS) was performed to quantify urinary iodide concentrations (n = 71) independently at McMaster University and Hamilton General Hospital, as well as the CDC as part of their quality assurance program. A positive bias in the original CE method was indicated, and buffer conditions were subsequently optimized to overcome matrix interferences for reliable iodine status determination. Results: Positive bias in CE was attributed to variable concentrations of sulfate, a major urinary anion interference with similar mobility to iodide under the conditions originally reported. By increasing the concentration of α-cyclodextrin in the background electrolyte, the CE method was able to tolerate urinary sulfate over its normal physiological range without loss in signal response for iodide. The optimized CE assay generated results that were consistent with ICP-MS using 2 different internal standards (187 Re and 130 Te) with a median bias under 10%. Conclusions: CE offers a simple, selective, and cost-effective separation platform for surveillance of the iodine status of a population requiring only small volumes (<10 μL) of biobanked urine specimens, which is comparable to previously validated screening methods currently used in global health initiatives for prevention of iodine deficiency disorders. IMPACT STATEMENT A capillary electrophoresis (CE) method presented here offers a simple, selective, and cost-effective microseparation platform for urinary iodide determination, which is essential to support global health initiatives for prevention of iodine deficiency disorders. An interlaboratory method comparison was performed to identify and address sources of bias, resulting in an optimized CE method that generated consistent results in comparison to the reference method, inductively coupled plasma-mass spectrometry (ICP-MS). The validated CE assay allows for continuous monitoring of iodine nutrition in populations that is applicable to volume-restricted urine samples without complicated sample workup, expensive infrastructure, or high operating costs.

Colorimetric Detection of Uranyl Using a Litmus Test

“…All trace elements standards were purchased from Sigma Aldrich (Oakville, Canada). Trace element measurements were conducted using the Agilent 8800 triple-quadrupole ICP-MS instrument (ICP-QQQ/Agilent Technologies, Tokyo, Japan) using a modification of a previously described protocol (Macedo et al, 2017 ). Briefly, calibration standards and water samples were prepared by a 3-fold dilution in 0.5% NH 4 OH (wt) containing 2% (wt) isopropanol, 0.025% (wt) EDTA, 0.025% (wt) Triton X-100 as well as internal standards (Bi, Ge, In, Li, Lu, Rh, Sc, and Tb) with an individual concentration of 420 μg/L.…”

The Prevalence and Risk Factors Associated with Iodine Deficiency in Canadian Adults

“…Urine samples were analyzed for iodide that is the predominant species of iodine excreted in urine, as well as nitrate and thiocyanate using a recently validated assay based on capillary electrophoresis with UV absorbance detection [34,35]. Urinary sodium concentrations were measured by indirect potentiometry using a Beckman Coulter UniCel DxC600 Synchron Clinical System [33].…”

“…Unmodified fused-silica capillaries were purchased from Polymicro Technologies Inc. (Phoenix, AZ, USA) with an internal diameter of 75 µm and total and effective (to detector window) capillary length of 60 cm and 50 cm, respectively. The background electrolyte (BGE) was composed of 180 mM lithium hydroxide, 180 mM phosphoric acid, 46 mM α-cyclodextrin with a pH of 3.0 [35]. New capillaries were initially conditioned by flushing with methanol, deionized water, 1.0 M lithium hydroxide (5 min each), and then background electrolyte (BGE) for 20 min using a rinse pressure of 20 psi (138 kPa).…”

“…In this work, we examined the iodine status in 24 h urine specimens collected from participants (n = 800) in the Prospective Urban and Rural Epidemiological (PURE) study [33]. A validated method based on capillary electrophoresis (CE) was used for simultaneous analysis of urinary iodide, nitrate and thiocyanate after a simple dilution step [34,35]. Our study aimed to identify risk/protective factors associated with iodine deficiency for participants residing in four communities across Canada reflecting differences in dietary habits, smoking status, and other environmental exposures.…”

Reliability of urinary charged metabolite concentrations in a large-scale cohort study using capillary electrophoresis-mass spectrometry

“…We have already reported the reliability and accuracy of plasma metabolites in cohort studies through another study conducted by us 13 . Previous studies have investigated the measurement reliability for urinary iodine 20 or urinary hydroxypyrene glucuronide 21 by CE-MS. However, there are few studies which comprehensively evaluate validation for urinary metabolites in large-scale epidemiological studies.…”