光度法测定食盐中碘——基于溴化钾催化的茜素红与碘酸钾的氧化褪色反应

Photometric Determination of Iodine in Table Salt by Oxidative Color-fading Reaction of Alizarin Red with KIO_3 Catalyzed by Potassium Bromide

在0．30mol·L-1盐酸介质中，碘酸钾在溴化钾的催化作用下氧化茜素红而使之褪色，且褪色程度与碘酸根含量呈线性关系，据此建立了测定食盐中痕量碘的方法。试验结果表明：茜素红的最大吸收波长为420nm，在1．07-19．3mg·L-1范围内，碘酸钾的质量浓度与吸光度变化值符合比耳定律。表观摩尔吸光率为2．47×10^4L·mol-1·cm-1。应用此方法测定了食盐样品中碘量，并测得方法的相对标准偏差（n=6）在3．4％～4．2％之间，回收率在95．1％～97．3％之间。

In 0. 3 mol· L-1 HCl medium, alizarin red was oxidized by KIO3 in the presence of KBr as catalyst, leading to decoloration of alizarin red. It was found that the magnitude of decrease in absorbance （AA） measured at 420 nm kept a linear relationship with the concentration of KIO3 in the range of 1.07-19.3 mg · L-1. Apparent molar absorptivity of the reaction system was found to be 2. 47× 10^4L·mol-1 · cm-1. Based on these facts, a photometric method for determination of iodine in table salt was proposed. Salt samples were analyzed by the present method, giving values of recovery in the range of 95.1%--97. 3%, and values of RSD＇s （n=6） in the range of 3. 4% to 4. 2 %.