[目的]探讨用二甲基黄褪色光度法测定酱类食品中微量碘的方法.[方法]将待测的酱类样品在碱性条件下进行灰化,碘被还原后与碱金属结合生成碘化物,再用溴水将碘化物定量氧化物碘酸钾,然后在酸性条件下,以溴化钾为催化剂,利用IO3-的氧化性使二甲基黄褪色,从而测定酱类食品中微量碘.[结果]在硫酸介质中,碘酸根对二甲基黄有褪色作用,且褪色程度与碘酸根的量在一定范围成正比关系.通过试验,确定了最佳试剂的用量:硫酸为3.50 ml,二甲基黄溶液为6.00 ml,溴化钾为3.00 ml;确定了最佳反应温度为90℃,反应时间为4min.标准曲线表明,在最大吸收波长510 nm处,碘测定的线性范围在0～1 μg/ml.[结论]该方法重现性好,准确度高,操作简便,用于酱类食品中碘含量的测定,结果令人满意.%[Objective] The study aimed to discuss the method of determining the iodine content in the soy sauce food by the color fading spectro-photometry. [ Method]The tested sauce samples were ashed under the alkaline conditions,the reduced iodine produced the iodide when combined with the alkali metal,then the iodide was quantitated into the oxide potassium iodate by using the bromine water,and then in acid condition,with the potassium bromide as the catalyst,the use of IO3- oxidation could fade the dimethyl yellow,thus to determine the trace iodine in the soy sauce food. [Result]In the medium of H2SO4,it was found that the iodate had the discoloration on the dimethyl yellow and its discoloration degree had a positive relation with the amount of the iodate in some range. Through the experiment,the optimum dosage of the reagents was confirmed as follows: sulfuric acid was 3.50 ml,dimethyl yellow solution was 6.00 ml,potassium bromide was 3.00 ml;the optimum reaction temperature and time were confirmed as 90℃ and 4 min resp. Standard curve showed that the linear range of the iodine determination was 0 - 1 μg/m at the maximum absorption wavelength of 510 run. [Conclusion]This method was good in the reproducibility,high in the accuracy,easy in the operation, which could get a satisfactory result when used in the determination of the iodine content in the soy sauce food.
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