Preferential solvation in acetonitrile–water mixtures Relationship between solvatochromic parameters and pK values of carboxylic acids

Abstract

Ionization constants of several carboxylic acids in acetonitrile–water mixtures, usually used as mobile phases in liquid chromatography (LC), have been obtained in order to predict the influence of pH on retention and selectivity in LC. In this work, the quasi-lattice quasi chemical (QLQC) theory of preferential solvation was applied to obtain the degree of preferential solvation of acetate ions in these media in order to explain the variation of the pK values obtained over the whole composition range studied. Also, the relationships between pK values and various macroscopic and microscopic properties were used to calculate pK values of the carboxylic acids in any acetonitrile–water mixture up to 70% (w/w) and, thus, to determine the acid–base behaviour of substances in the widely used acetonitrile–water media.