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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.
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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.
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Objective To establish a catalytic spectrophotometric method for determination of iodine in water without the use of highly toxic arsenic reagents with good precision and accuracy.Methods A new flow injection catalytic spectrophotometry method for determination of iodine in water was established by combining flow injection analysis (FIA) with a new catalytic spectrophotometry for determination of iodine with no need of arsenic reagent.The standard curve linearity,sample detection limit,precision and accuracy of different iodine content ranges (0-250,0-1 200 μg/L) were tested.The test result was compared with that of the arsenic-based catalytic spectrophotometry recommended by the iodine deficiency disorders monitoring program in China (recommended monitoring method).Results A calibration relation of C =aA2 + bA + d (C:iodine concentration,A:measuring absorbance peak area from FIA) of the new method existed in the range of 0-250 and 0-1 200 μg/L.The linear correlative coefficient were both 0.999 9.The detection limit for iodine in water was 0.3 μg/L.The FIA peak shape of the sample tube with the lowest content is determined,and the sensitive iodine signal is detected.The water samples with different iodine content ranges were determined in parallel for 6 times,and the coefficient of variation (CV) was 0.2％-2.7％;the recoveries ranged from 95.0％ to 105.0％,and the total average recovery was 100.3％.The measured values of water iodine standard material GBW 09113e [(8.2 ± 1.2) μg/L] and GBW 09114d [(62.0 ± 6.0) μg/L] in the standard curve of different iodine contents were all within the uncertainty range of the given value.There was no significant difference between the results of recommended monitoring method and the new method (t =0.781,P ＞ 0.05).Conclusions The new method for measuring water iodine has a wide standard curve range,high sensitivity,and good precision and accuracy.The instrument is easy to operate,and no need for toxic arsenic reagent.The method is a reliable method for water iodine detection.
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Objective To establish a catalytic spectrophotometric method for determination of iodine in urine without the use of highly toxic arsenic reagents and with good precision and accuracy. Methods Combined flow injection analysis (FIA) with new catalytic spectrophotometry, a new method for determination of iodine with no need of arsenic reagents was developed by the author. An ammonium persulfate digestion-flow injection catalytic spectrophotometry for determination of iodine in urine was established. Standard serial solutions and urine samples were all digested by ammonium persulfate before testing. The standard curve linearity in the range of 0-1200μg/L, detection limit,precision and accuracy in determining urinary iodine were tested. Results A good calibration relation of C=aA2+bA+d (C:iodine concentration,A:measuring absorbance peak area from FIA) of the newly developed method existed in the range of 0 - 1200 μg/L. The linear correlative coefficient was 0.9998. The FIA analysis speed was 60 samples per hour. The detection limit for urinary iodine was 7.1μg/L. Precision:The intra-assay coefficients of variation (CV) were 0.3％ - 3.0％ (n = 6) when measuring 9 urine samples with iodine concentration of 61.8-806.8μg/L;the intra-assay CV were 0.2％-1.7％(n=6) when measuring 5 urinary iodine national standard materials with iodine concentration of 76.9 - 883.0 μg/L; the inter-assay CV were 1.0％ - 1.2％ when measuring 6 batches of 3 urinary iodine national standard materials with iodine concentration of 76.9 - 232.0 μg/L. Accuracy:The average recovery rate was 98.3％ with a range of 91.2％ - 104.6％ when measuring 20 urine samples with iodine concentration ranged from 18.9 to 807.1 μg/L. The test results of 5 urinary iodine national standard materials were all within the given value range and the relative deviations ranges were-2.9％-0.7％. No significant difference was found between the results of the 48 urine samples determined by the current standard method (WS/T 107.1-2016) and the new method (t=0.029, P>0.05). Conclusions The new method has a wide standard curve range, high sensitivity, good precision and accuracy, and is simple and easy to operate, with automatic sampling, rapid analysis, and no need for toxic arsenic reagent which is difficult to obtain and can pollute the environment. The method is suitable for widely application and can be used as a reliable technical method for urinary iodine detection.
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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.
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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.
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Objective To determine the iodine content of iodine-rich herbal and analyze the effective factors.Methods Iodine contents of seaweed at different alkali ashing temperature,such as 200℃,300℃,400℃,500℃and 600℃were determined,then the optimum ashing temperature were selected.Mixed ashing auxiliary including potassium carbonate,zinc sulfate,sodium chloride,potassium chlorate were added in samples of iodine-rich herbal,and ashed at the optimum ashing temperature for 2h.The ash was dissolved in deionized water.Iodine content of iodine-rich herbal was determined with As3+-Ce4+catalytic spectrophotometry.Results The optimum ashing temperature was 300℃;the standard curve regression equation:A =-6.91 ×10 -3C +1.0306,r =0.999 3;iodine content of seaweed,Kunbu and Haidai was 0.829 mg/g,0.343 mg/g and 0.864 mg/g respectively;recovery rates before ashing of seaweed,Haidai and Kunbu were 83.19%,81.47% and 80.32% respectively;91.24%,93.43% and 95.86% after ashing.Conclusion Iodine is rich in iodine-rich herbal,the optimum ashing temperature is 300 ℃,and As3+ -Ce4+ catalytic spectrophotometry is stable and accurate as a determination method of iodine content of herbal.
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A catalytic spectrophotometric method for determination of trace molybdenum by flow injection analysis has been established, based on the catalytic oxidation of potassium iodide by hydrogen peroxide in the presence of molybedenum (VI) and the iodine produced is coloured with starch. The linear range and detection limit for molybdenum (VI) were 0 to 0.4 ppm and 3.2 ppb. The method has been successfully applied to determine molybdenum in the grain, soil and hair.