柠檬酸铁(Ⅲ)络合物的光致变色现象与柠檬酸的测定

Photochromism of Ferric Citrate Complex and Determination of Citric Acid

报道了柠檬酸铁（Ⅲ）络合物的光致变色现象并将其应用于微量柠檬酸（或盐）的测定。在 PH1.8～2．5的酸性介质中，柠檬酸与 Fe3+生成的黄色络合物在光照下发生光致变色生成紫色络合物，其最大吸收波长为 490 um，表观摩尔吸光系数ε为 805 L·mol-1·cm-1；络合物的组成比为 １：１方法的线性范围为 0～250 mg/L。用此法测定了几种饮料中的柠檬酸含量，结果令人满意。

A novel spectrophotometric method is reported for the determination of micro amounts of citrate. In acid medium of pH 1. 8-2. 5, the yellow ferric(Ⅲ) citrate complex changes into a violet complex based on photochromism. The ratio of citrate to Fe3+ is 1: 1 in the complex. Its apparent molar absorptivity is 805 L. mol-l. cm--1 at 490 nm. The calibra- tion graph is linear for 0-250 mg/L. The proposed method has been applied to the spec- trophotometric determination of citric acid in aerated water with satisfactory results.