Practical methods for the measurement of log P for surfactants

摘要

Hydrophobicity is a commonly used parameter in quantitative structure activity relationships. The ability to determine the octanol-water partition coefficient (log P) empirically for non-ionizing, non-surfactant type chemicals using traditional stir-flask methods has been successful and well documented. In comparison the ability to measure log P for surfactants is considered impractical due to their amphiphilic nature, which gives them a tendency to form micelles and reside at the octanol-water interface. In this study we have shown that working with compounds below their critical micelle concentrations (CMC), at the experimental concentrations, it is possible to obtain experimental log P values for a series of sulphobetaines using the stir-flask method coupled with reversed phase-high performance liquid chromatography (RP-HPLC). Until now the ability to verify calculated log P values for surfactants has been limited. Measuring log P as described here can now be applied to other surfactants to validate existing and new modifications to the fragment method.