Determination of Dissociation Constants of Some Hydroxylated Benzoic and Cinnamic Acids in Water from Mobility and Spectroscopic Data Obtained by CE-DAD

Abstract

In this study, the dissociation constants of a series of phenolic acids, including benzoic acid, four hydroxylated derivatives (p-hydroxybenzoic, protocatechuic, vanillic, and gallic), and four hydroxylated cinnamic acid derivatives (p-coumaric, caffeic, ferulic, and sinapinic) have been determined in water by capillary electrophoresis (CE) from the electrophoretic mobilities at different pH value. The pKa values have also been obtained from the absorbance spectra at the maximum of the electrophoretic peaks, which were measured with a diode-array detector (CE-DAD methodology). The pKa values obtained from both methodologies (CE and CE-DAD) have been compared with those previously published in the literature and also with the values predicted by the SPARC online pKa calculator.