Use of Inductively Coupled Plasma Mass Spectrometry to Measure Urinary Iodine in NHANES 2000: Comparison with Previous Method

Abstract

Urinary iodine (UI) concentrations directly reflect dietary iodine intake and consequently test biochemical assessment of the iodine status worldwide (1). The Iodine Laboratory of the Division of Laboratory Sciences at the National Center for Environmental Health, CDC, measured the UI content of specimens as part of the National Health and Nutrition Examination Survey (NHANES) 2000 and will measure UI in the US population through future NHANES analyses, using inductively coupled plasma mass spectrometry (ICP-MS). In this report, we describe the ICP-MS laboratory method and compare that method with the established Sandell–Kolthoff (S-K) spectrophotometric method used in NHANES III. The ICP-MS method described previously (2) was modified for use in NHANES 2000 by adding alkaline diluents and rinses to measure UI as follows: urine samples and the urine iodide calibrator solutions were prepared just before analysis by dilution (1:49; 50 μL of sample/calibrator plus 2450 μL of diluent) with an aqueous solution of 10 mL/L tetramethylammonium hydroxide containing 10 μg/L tellurium as an internal standard. A peristaltic pump introduced the diluted samples into the spray chamber with an argon stream. The I+ and Te+ ions were measured at m/z 127 and 130, respectively (3). The diluent used to make the intermediate working calibrators was 1.0 g of analytical-reagent-grade sodium thiosulfate (Na2S2O3) dissolved in 1000 mL of 18 MΩ · cm ultrapure water. (The water used for all dilutions and rinses in the ICP-MS method is ultrapure 18 MΩ · cm water; Millipore Corporation.) The wash solution was an aqueous solution of 1 mL/L Triton X-100 and 10 mL/L tetramethylammonium hydroxide. This solution was …