Chemical kinetics study and application of a method with low usage amount of arsenic trioxide for determining urinary iodine by arsenite-ceric catalytic spectrophotometry using ammonium persulfate digestion / 中国地方病学杂志

ABSTRACT

Objective To study the chemical kinetics characteristics in a new revised method with low usage amount of arsenic trioxide for determining urinary iodine by arsenite-ceric catalytic spectrophotometry using ammonium persulfate digestion,and to study the impact of operating bias in arsenite-ceric reaction temperature and reaction time on final results in this method.Methods The absorbances (A) of arsenite-ceric reaction of iodine standard series were measured at different reaction temperature and time,and the results were analyzed according to the chemical kinetics equation.The change values and half-life of A values of the new revised method and the current standard method were calculated.The chemical kinetics model of reaction system for this new revised method was deduced from experimental results.The calculation formula of result relative error for urinary iodine determination was deduced based on constants reaction temperature and reaction time and reaction rate constant factor.The result relative errors caused by operation deviation of reaction temperature or reaction time in the determination of urinary iodine were calculated.Results The usage amount of arsenious acid solution in the new revised method was only a quarter of usage amount of the current standard method(WS/T 107-2006).A values of each concentration of standard curve series at different reaction time t were obtained,the lnA to t mapping was a straight line,the linear correlation coefficients were-0.9995--0.9999.These results were in accord with the characteristic of chemical first-order reaction.Relationships between the reaction rate constant K and the reaction temperature T in the temperature range of 20-35 ℃ were well accord with Arrhenius equation.The A values and iodine concentrations (C) at various experimental temperatures showed good C =a + blnA linear relation,the absolute value of the linear correlation coefficient(｜ r ｜) ＞ 0.9990.After calculation and comparison of changes in the half-life of A values in the new revised method and in the original standard method at 20,25,30,35 ℃ reaction temperature,half-life of A values of 0-300 μg/L iodine standard series in the new revised method and in the original standard method were 191.0-11.4 min and 66.8-10.2 min at 25℃,respectively.Under the same conditions of 25 ℃ for 40 min,the gradient of A values of 0-300 μg/L iodine standard curve in the new revised method was similar to that of the original standard method(slope-133.7,-139.2,respectively).But differences between A values of standard curve and the reaction initial absorbance(A0) in the original standard method were 1.4 to 3.7 times those of the new revised method.A chemical kinetics model of reacting system for this method was established.A series of urinary iodine results relative error data were obtained when reaction temperature deviation was ± 1,± 0.5,± 0.3 ℃ or reaction time deviation was ± 1 min for sample test tubes.Data showed that relative errors of urinary iodine results caused by reaction temperature deviation or reaction time deviation in the new revised method were less than those of the original standard method.Conclusions The iodine-catalyzed arsenite-ceric reaction in the new revised method is a first-order reaction,when measuring 0-300 μg/L urinary iodine at 20-35 ℃,and 300-1200 μg/L urinary iodine at 20-30 ℃,the calibration relation of C =a + blnA is established when arsenite-ceric catalytic spectrophotometry is kept at a certain stable temperature and in certain stable reaction time.Compared with the original standard method,using the revised method with low usage amount of arsenic trioxide for measuring urinary iodine,the arsenite-ceric reaction rate is slow down.As a result,this method is easier to operate and has better precision and accuracy.