Problems in urinary lodine determination methods and an automated kinetic assay as a solution
Problems in urinary lodine determination methods and an automated kinetic assay as a solution
Accurate, fast and economical urinary iodine measurement is very important in diagnosing iodine deficiency disorders. The urinary iodine determination method using ammonium persulfate digestion based on the Sandell-Kolthoff reaction was optimized and modified to kinetic and automated assay. Ammonium persulfate digestion was performed at +95 °C in a water-bath to ± 0.1 °C precision. The performance of both the Sandell-Kolthoff reaction at 37 °C and its kinetic measurement at 340 nm was tested in a random access automated analyzer. For method comparison, urinary iodine concentrations were measured using both the conventional chloric acid digestion method and the kinetic automated method in 66 randomly selected apparently healthy peoples' urine samples and five working iodine calibrators.The method agreed well with the conventional chloric acid digestion method (n = 66; r = 0.937 ;y = 0.895x + 0.149; Sy/x = 0.136). The detection limit of assay was 0.10 $mu$mol/L. The mean recovery of iodine was 97% (87-107%). The intra- and intera ssay CVs for samples with iodine concentrations between 0.20 and 3.14 $mu$mol/L were $leq$ 10%. Our study suggested that urinary iodine should be determined by kinetic reading at 340 nm wavelength in an automated analyzer instead of by manual endpoint measurement at 410 nm.The kinetic procedure presented here therefore offers an easier, faster, more accurate.and more economical method.
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- 1. Sandell EB. Kolthoff IM. Microdetermination of iodine by catalitic method. Microchem Acta 1: 9- 25.1937. 2. Zak B.Willard HH.Myers GB.Boyle AJ. Chloric acid method for determination of protein-bound iodine. Anal Chem 24: 1345-8.1952. 3. Pino S. Fang S. Braverman LE. Ammonium persulfate; a safe alternative oxidizing agent for measuring urinary iodine. Clin Chem 42: 239-43.1996. 4. Bland JM. Altman DG. Statistical methods for assessing agreement between the methods of clinical measurement. Lancet i: 307-10.1986. 5. Ohashi T. Yamaki M. Pandav CS. Karmarkar MG. Irie M. Simple microplate method for determination of urinary iodine. Clin Chem 46: 529- 36.2000.