Ammonium persulfate: a new and safe method for measuring urinary iodine by ammonium persulfate oxidation

The chloric acid method is most commonly used to obtain accurate and reproducible measurements of iodine and removes 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 using 1 mol/L ammonium persulfate, a non-explosive, non-hazardous chemical, as the oxidizing reagent. The oxidation procedure can be completed in 30 minutes at a temperature of 91-95 degrees C. The iodine in the urine is then measured by a modification of the traditional colorimetric method of Sandell-Kolthoff. 110 urine samples collected from a mixed population of healthy males and females, ranging in age from 6 to 79 years and living in the United States were analyzed for iodine content by two methods: the proposed ammonium persulfate method and the chloric acid method. The ammonium persulfate method has an intra assay CV of 9.1% at 0.42 +/- 0.04 micromol/L (mean +/- SD), 7.8% at 1.46 +/- 0.11 micromol/L and 4.0% at 3.54 +/- 0.14 micromol/L. The inter assay CV is 10.2% at 0.46 +/- 0.05 micromol/L and 7.9% at 3.27 +/- 0.26 micromol/L. Recovery of iodine added to urine in vitro was 107%, 94% and 97% for 0.42 micromol/L, 0.77 micromol/L and 3.64 micromol/L, respectively. The lower limit of detectability was 0.0034 microgI. Values for iodine in 110 urines measured by the reference chloric acid method ranged from 0.06 to 8.03 micromol/L and by the ammonium persulfate method from 0.05 to 7.4 micromol/L. The persulfate method (y) correlated extremely closely with the reference chloric acid method (x) by the Pearson correlation (y = 0.923x + 0.810 micromol/L, and r = 0.994, Syx = 1.841). In conclusion a new, safe, simple method for measuring urinary iodine is described which uses ammonium persulfate as the oxidizing agent for the removal of interfering substances.