A rapid screening assay determination of octanol-water partition coefficients (log P) of pharmaceuticals was developed by using microemulsion liquid chromatography (MELC). Seven standard compounds with known log P values were used for constructing the calibration curve of log P against the MELC log k, by which the log P values of the pharmaceuticals were calculated. The types of surfactants and oil phase were evaluated in the microemulsion systems using such parameters as linear correlation coefficients the literature log P values against the experimentally measured log k values. The optimized MELC system with microemulsion consisting of 6.0% polyoxyethylene lauryl ether (Brij35)-6.6% butanol-0.8% octanol-86.6% phosphate buffer (0.05 mol•L－1, pH 7.0) shows good correlation (r＝0.96) to the experimental log P (Elog P) values for noncongeneric neutral and basic pharmaceuticals. The average error of log P values measured by MELC is within 0.3 log unit of the values from the literature. The results indicate that MELC can serve as a high throughput, reliable and robust approach and as a valid model for log P determinations.

Key words: microemulsion liquid chromatography, oil-water partition coefficient, log P