薄层色谱pH法测定有机酸的电离常数

在薄层色谱pH法中 ,利用固定相的 pH值与待测组分Rf值的关系 ,导出了 pH Rf曲线方程 ,依此方程 ,计算出 3种一元有机酸的电离常数 ,所得结果与文献值基本一致〔4〕

The Determination of Ionization Constants by Thin-Layer pH-Chromatography

An ionization constant of a dissocating compound is one of the important parameters in evaluating its physicochemical properties.It can tell the percentage of molecular ionized form for a dissociating compound with a given pH value.Potentiometric titration and spectrophotometry are commonly used in determining ionization constants.The method used in this article is called thin layer pH chromatography a method founded on the relationships between the Rf value of a dissociating compound and its pH value of chromatographic system.Experiments were carried out on three organic acids:benzoic acid,4 methylbenzoic acid and 3 nitrobenzoic acid to determine their ionization constants;buffering solutions with different pH were used as the stationary phase,chloroform mixed with ether was used as the mobile phase.Experimental data were similar to those in the literature.It needs only simple instruments with high accuracy,and is especially suitable for the ionization constant determination of an unkown mixture which is difficult to separate.