Effects of sample digestion conditions on urinary iodine measurement results

Abstract

Objective To study the effects of sample digestion conditions on measurement results of urinary iodine determined by As(Ⅲ)-Ce4+ catalytic spectrophotometry with ammonium persulfate digestion,and to promote the application of newly revised (the 2012 edition) national standard method for determination of urinary iodine.Methods According to the newly revised national standard method,various digestion conditions,such as ammonium persulfate concentration (0.8-1.3 mol/L,group interval 0.1),digestion instruments (heating block and drying oven) and standing time after digestion(0.5,1.0,2.0,4.0 and 22.0 h),were studied.The samples included 3 standard materials,which were GWB09108k,GWB09109f and GWB09110m containing iodine of (68.2 ± 9.0),(138.0 ± 10.0) and (221.0 ± 10.0) μg/L,and 5 urine samples with iodine concentration of 100-300 μg/L.Results Measurement results among the three groups of 0.9,1.0 and 1.1 mol/L ammonium persulfate digestion fluid showed no significant difference(P ＞ 0.05).The digestive effect showed no significant difference between heating block and drying oven (P ＞ 0.05) except one standard material in low concentration (GBW09108k).After digestion,samples were placed 0.5-22.0 h,the measurement results between groups showed no significant difference (P ＞ 0.05).Conclusions Appropriate concentrations of ammonium persulfate are from 0.9 mol/L to 1.1 mol/L.Heating block is recommended for the digestion,however,when absent,drying oven can be used alternatively.The standing times from 0.5 h to 22 h after digestion have not affected the measurement results. Key words: Urine ; Iodine ; Methods ; Digestion conditions; Ammonium persulfate