Determination of lipophilicity by reversed-phase high-performance liquid chromatography. Influence of 1-octanol in the mobile phase.

Lipophilicity was evaluated using a novel RP-HPLC stationary phase (Discovery-RP-Amide-C16) with and without 1-octanol added to the mobile phase. A set of 46 drugs and flavonoids characterized by a broad structural diversity and a wide log Poct range (-0.69 to 5.70) was selected for this study. This set consists of neutral solutes and solutes with acidic or ampholytic functionalities which were maintained neutral at pH 2.5 or 4. In our conditions, the addition of 1-octanol in the mobile phase proved a key factor to derive a lipophilicity index log k(w) highly correlated with log Poct for all investigated solutes. 1-Octanol improved the correlation between log Poct and log k(w) mainly by influencing the retention behavior of the solutes with log Poct values below +3. This study brings additional evidence that under proper experimental conditions of stationary and mobile phases, RP-HPLC is a very useful method to obtain log Poct values.