Estimation of the octanol–water distribution coefficient of acidic compounds by microemulsion electrokinetic chromatography

Publication date: Available online 11 November 2019Source: Journal of Pharmaceutical and Biomedical AnalysisAuthor(s): Alejandro Fernández-Pumarega, Susana Amézqueta, Elisabet Fuguet, Martí RosésAbstractThe feasibility of extending the determination of the lipophilicity of partially ionized acids (log Do/w) by microemulsion electrokinetic chromatography (MEEKC) is tested. Theoretical considerations predict that a linear log Do/w vs. log k correlation can be obtained only when the neutral and ionic forms of an acid follow the same correlation equation and the slope of the correlation is unity. In practice, since the lipophilicity of the neutral acid is much higher than that of the ionic form and the correlation slope is not very different from 1, the general linear correlation for neutral compounds can be applied across most of the ionization range of the acid.The linear correlation between log Po/w and log k of 20 neutral solutes has been established and extended to 6 acids used as models, tested across their full ionization range. log Do/w-pH, and log k-pH profiles have been obtained for these 6 acids, and plotted log Do/w against log k for any acid at any degree of ionization. Furthermore, the log Do/w of the acids has been estimated from the calibration curve and log k-pH profile, and compared to values in the literature determined using reference methods such as the shake-flask one. Accurate values have been obtained using the MEEKC method when the acids are in their ...
Source: Journal of Pharmaceutical and Biomedical Analysis - Category: Drugs & Pharmacology Source Type: research