Hydrophobicity parameter (log Kow) estimation for some phenolic compounds of pharmaceutical interest from retention studies with mobile phase composition in reversed‐phase liquid chromatography

Chromatographic retention of some phenolic compounds (impurities of related pharmaceutical active substances) was studied for different organic modifier contents in mobile phase. Their capacity factors k' versus organic modifier content (acetonitrile, or methanol) in mobile phase were measured and the corresponding dependences were studied by linear and polynomial regressions and then they were extrapolated to a mobile phase with no content in organic modifier in order to estimate their octanol/water partition coefficient (log Kow).
The values of log Kow from retention data were compared to known shake-flask experimental values and theoretical values predicted by fragment methodology. Linear dependences for methanol and second-degree polynomial dependences for acetonitrile between organic modifier volume percentage and log k' provided
good estimation of log Kow. The chromatographic method can be considered as a method of choice for estimating hydrophobicity parameter for different solutes. The linear dependence between extrapolated values of log k' for 0% organic modifier and log Kow estimated by means of fragment methodology for the model compounds can be used to predict chromatographic retention of other similar compounds.