碱灰化砷铈催化分光光度法测定食品中碘含量

Measurement of iodine content in food by As^(3+)-Ce^(4+) catalytic spectrophotometry withdry ashing of sample preparation

目的建立一个食品中碘的测定方法。方法使用碳酸钾、硫酸锌、氯酸钾、氯化钠混合碱性助剂于550℃灰化样品4 h,用水溶解灰份后取上清砷铈催化分光光度法测定碘含量。根据光密度值的对数与碘含量成线性关系计算样品中的碘含量。结果检测范围为5~250 ng碘;标准曲线的平均相关系数为0.999 6;精密度:测定样品碘含量为84.4、134.4、258.5μg/kg时,其变异系数(CV)分别为7.0%、1.9%、1.2%(n=6);准确度:对低、中、高3种不同碘含量的样品加碘标回收率分别为106.0%、94.9%、100.4%(n=6)。结论本方法适宜于食品中总碘的测定。

Objective To research a new method for determination of food iodine in range of 5 - 250 ng by As^3＋ -Ce^4＋ catalytic spectrophotometry with dry ashing of samples in KClO3 - ZnSO4, - K2 CO4 - NaCl. Methods The mixture of foodstuff powder and the solution of KClO33 - ZnSO4 and K2 CO3 - NaCl is heated in dry bath at 105℃ for around 3 hours, then heated by a adjustable electric heater at 300 - 600 W until all black fog is completely released, transferred into muffle furnace for ashing at 550℃ for 4 hours. The dissolved ash is measured by As^3＋ - Ce^4＋ catalytic spectrophotometry. Results This testing covers iodine ranged from 5 ng to 250 ng. The relevance coefficient of standards is 0.9996. The coefficients of variation are 7.0%, 1.9% and 1.2% （ n =6） respectively when 84.4μg/kg, 134.4μg/kg and 258.5 μg/kg of the iodine contents of samples are tested. The average recovery is 100.4%（94.9% - 106.0% ）. Conclusion This method is suitable to measure food iodine and easier to be porfonned with better precision and accuracy.