This work evaluates the use of relative mobility to estimate octanol-water partition coefficients (lg P_o/w) of drugs using peak-shift microemulsion electrokinetic chromatography (MEEKC). The lg P_o/w of 5 compounds with different hydrophobicity were determined by the use of relative mobility and compared with the results obtained by the use of absolute mobility. Furthermore, the developed method was applied to determine the lg P_o/w values of 3 drugs, and the average error between the literature value and value determined by relative mobility was 0.18. The result shows that the errors caused by the change of the viscosity and the fluctuation of applied voltage, current and temperature in the experiment could be avoided by the use of relative mobility to describe the analyte migration in MEEKC. The proposed method was an alternative approach to estimate the hydrophobicity of drugs.

Key words: relative mobility, octanol-water partition coefficient, microemulsion electrokinetic chromatography