Résumé
Objective:To establish a method for automatic determination of iodine level in salt by arsenic-cerium catalytic spectrophotometry using an iodine element detector (hereinafter referred to as this method), and to provide reference for in-depth study of salt iodine detection technology.Methods:This method was used to determine the iodine level in salt, and the linear range, detection limit, precision, and accuracy (determination of salt iodine standard substance GBW10006y and GBW10007y, and addition recovery experiment) of this method were determined. The iodine level of 35 salt samples was determined by this method and redox titration method recommended by the national standard, and the results were compared.Results:This method had a good linear relationship within the range of 50 - 600 μg/L standard curve, the absolute value of the correlation coefficients was > 0.999 0, and the detection limit was 5.0 mg/kg. The relative standard deviation of iodine concentration in salt samples with low, medium and high iodine concentrations were all < 6.0%. The determination results of salt iodine standard substance GBW10006y and GBW10007y were within the given value ranges; three iodine concentrations (6.0, 10.0 and 30.0 mg/kg) were added to the salt samples, with an average recovery rate of 96.7% to 105.0%, and a total average recovery rate of 100.9%. The method comparison experiment showed that there was no statistically significant difference between the salt iodine determination results of this method and the redox titration method ( t = - 1.54, P = 0.132). Conclusion:This method has the advantages of high accuracy, good precision and wide linear range in determining salt iodine, and is suitable for the detection of large quantities of samples in salt iodine monitoring.
Résumé
Objective:To establish a method for determination of iodine in salt by arsenic-cerium catalytic spectrophotometry.Methods:The content of iodine in salt was detected by arsenic-cerium catalytic spectrophotometry with an automatic iodine analyzer. The standard curve linearity, detection limit, precision and accuracy of the method were evaluated. The iodine content of 20 edible salt samples was detected by the newly established method and direct titration, and the results were compared.Results:In the range of 0 - 150 μg/L standard curve, the correlation coefficient ( r) = - 0.999 9, and the detection limit was 1.4 mg/kg. The average iodine contents of iodine composition analysis standard materials GBW10006z and GBW10007z were 12.2 and 22.8 mg/kg ( n = 6), respectively, which were all within the given standard value ranges, and the relative standard deviations ( RSD) were 2.04% and 2.33%, respectively. Iodine composition analysis standard materials GBW10006b, GBW10007b, GBW10006v, GBW10007v, GBW10006z and GBW10007z measurement results (12.0, 24.6, 12.6, 22.8, 12.3, 23.2 mg/kg, n = 2) were all within the given standard value ranges, with good quality control. The iodine content of 20 edible salt samples was detected by arsenic-cerium catalytic spectrophotometry and direct titration, respectively, and the difference was not statistically significant ( t = 1.99, P = 0.060). Conclusion:Arsenic-cerium catalytic spectrophotometry has the characteristics of good linear relationship, low detection limit, good precision and high accuracy in determination of salt iodine content, which is suitable for popularization and application.
Résumé
Objective By studying the variation of individual urinary iodine concentration due to different ways of urine sample collection to optimize it for standard clinical evaluation.Methods Totally 20 healthy adults were recruited and their urine samples were collected as a random urine sample within 1 day,the 24 hour urine and morning urine samples within 5 successive days,respectively.The coefficient of variation in each group was calculated.Paired t test was used to compare the results of 24 hour urine with the results of random urine and that of morning urine samples,respectively.Results The range of individual coefficient of variation for random urine sample within one day was 12.5％-57.4％,while most of the coefficients of variation were around 30.39％.In contrast,the individual coefficients of variation of morning urine sample and 24 hour urine results within 5 days were 5.4％-26.0％ and 3.4％-16.6％ and most of them were at about 11.74％ and 7.91％.The paired t test showed that the results of random urine sample were significantly different compared with that of 24 hour urine (t =-4.231,P ＜ 0.05).On the other hand,there was also significant difference for the results of morning urine compared with that of 24 hour urine (t =3.884,P ＜ 0.05).Conclusion This study suggests that 24 hour urine is the most appropriate way of sample collection for individualized detection of urinary iodine.
Résumé
Objective To establish a catalytic spectrophotometric method for determination of iodine in water using the same arsenious acid solution and ceric ammonium sulfate solution as those used in the 2016 version standard method for determination of urinary iodine,and to meet the needs of wide concentration range of water iodine detection.Methods After pretreatment of the water sample with the effective chlorine of sodium dichloroisocyanurate solution for eliminating the interference of reducing substances at room temperature,the concentration of iodine in water was determined by arsenic cerium catalytic spectrophotometry using the same 0.025 mol/L arsenious acid solution and 0.025 mol/L ceric ammonium sulfate solution as those used in the 2016 version standard method for determination of urinary iodine.The linear relationship of the standard curve and the linear rang of different iodine concentration range (0-100,0-400,0-800μg/L),the detection limit,the precision and the accuracy of the sample were tested.Results The calibration relation of C =a + blgA (C:iodine concentration,A:measuring absorbance) in the new method existed when arsenic cerium catalytic reaction was kept at a certain stable temperature ranging from 15 ℃ to 30 ℃ in certain stable reacting time.The linear correlative coefficients absolute value of different iodine concentration range (0-100,0-400,0-800 μg/L) were all greater than 0.999 0,corresponding to the water iodine detection limits were 0.3 μ,g/L (sample volume of 0.80 ml),1.2 μg/L (sample volume of 0.20 ml),and 2.2.μg/L (sample volume of 0.10 ml),respectively.The coefficients of variation (CV) of the three different iodine concentration range were all below 1.0％ (n =6).The iodine recovery rate range of a total of 10 different water samples in these three different concentration range was 95.8％-98.7％,98.3％-103.7％ and 98.5％-104.5％,and the average recovery rate was 97.6％,100.4％ and 102.4％,respectively.In the range of these three different standard curves,water iodine standard materials GBW09114c,GBW09114a and GBW09113c were measured.The relative errors between the results and the given values were ＜ 3.0％,which were in the range of uncertainty of the given value.Conclusion This method verified by methodology experiments has wide linear range,high precision,accuracy,and anti-interference ability,good reproducibility,and is easy to operate,with reduced amount of arsenic waste,reduced environmental pollution,and is suitable for application in different areas to determine water iodine.