Ammonium persulfate: A safe alternative oxidizing reagent for measuring urinary iodine

Abstract

The chloric acid method is most commonly used to obtain accurate and reproducible measurements of iodine and remove interfering substances. Unfortunately, chloric acid is a potential hazard, requiring an explosion- proof hood, among other precautions. We have developed a simple, convenient, and economic method for measuring urinary iodine by using 1 mol/L ammonium persulfate, a nonexplosive, nonhazardous chemical, as the oxidizing reagent. The oxidation procedure can be completed in 30 min at a temperature of 91-95 °C. The iodine in the urine is then measured by a modification of the traditional colorimetric method of Sandell and Kolthoff. Urine samples (110) collected from a mixed population of healthy males and females, ranging in age from 6 to 79 years and living in the US, were analyzed for urine iodine content by two methods: the proposed ammonium persulfate method and the chloric acid method. The ammonium persulfate method has an intraassay CV of 9.1% at 0.42 ± 0.04 μmol/L (mean ± SD), 7.8% at 1.46 ± 0.11 μmol/L, and 4.0% at 3.54 ± 0.14 μmol/L. The interassay CV is 10.2% at 0.46 ± 0.05 μmol/L and 7.9% at 3.27 ± 0.26 μmol/L. Recovery of iodine added to urine in vitro was 107%, 94%, and 97% for 0.42 μmol/L, 0.77 μmol/L and 3.64 μmol/L, respectively. The lower limit of detectability was 0.0034 μg of iodine. Values for iodine in 110 urines measured by the reference chloric acid method ranged from 0.06 to 8.03 μmol/L and by the ammonium persulfate method from 0.05 to 7.4 μmol/L. The persulfate method (y) correlated extremely closely with the reference chloric acid method (x) by the Pearson correlation (y = 0.923x + 0.810 μmol/L, and r = 0.994, S(y|x) = 1.841).