无中性标记物的毛细管电泳离解常数测定方法

系统研究了无需借助中性标记物的毛细管区带电泳测定离解常数的方法。记录电泳过程中流经毛细管柱溶液电流随时间的变化,发现存在两个电流突跃。其中第二个电流突跃所对应的迁移时间,与样品中不带电荷的中性物质的迁移时间相当;当样品中不含(也未添加)中性物质时,只要按照电泳实验中普通的溶样方式(用水、有机溶剂或稀释的背景电解质溶液作为溶剂),样品区带电导必然小于背景电解质溶液的电导,也会观察到第二个电流突跃。利用第二个电流突跃,并结合分析物的迁移时间,可求出分析物在不同酸度条件下的淌度值,进而用淌度值与pH及Ka间的非线性依赖关系,进行非线性拟合求出相应的离解常数。文中测定了几种有机酸碱的离解常数,结果与文献值吻合。

Determination of Dissociation Constant by Capillary Zone Electrophoresis without Addition of Neutral Marker

A method was systematically studied for determination of dissociation constant by capillary zone electrophoresis without addition of neutral marker.From the evolution of electrical current in the solution filled with capillary and buffer reservoirs at the ends of capillary,two significant jumps in electrical current could be observed.It was demonstrated that the migration time at second jump was equivalent to the migration time of neutral compound in the sample.Even though no neutral component and no addition of neutral component to the sample,the second jump in electrical current was also observed if the sample dissolved in water,organic solvent and diluted background electrolyte solution.The mobilities of analytes at different pHs can be calculated based on the second jump and migration times for analytes,and then dissociation constant was obtained by non-linear regression based on the dependent relationship between mobility and pH together with Ka.The dissociation constants for several organic weak acids and bases were determined by the method described here,and the results were in agreement with the data published in literatures.