Estimation of octanol-water partition coefficients for neutral and weakly acidic compounds by microemulsion electrokinetic chromatography using dynamically coated capillary columns.

Microemulsion electrokinetic chromatography (MEEKC) using dynamically coated capillary columns is shown to be suitable for estimating the octanol-water partition coefficient (log P) for neutral and weakly acidic compounds at pH 3. The solvation parameter model is used to demonstrate that the retention properties of sodium dodecyl sulfate (1.4% w/v), n-butanol (8% v/v) and n-heptane (1.2% v/v) microemulsion are strongly correlated with the octanol-water partition system. For compounds of varied structure and log P values from 0.3 to 5.15, the correlation model is able to estimate log P to better than 0.25 log units. The dynamically coated columns consisting of a bilayer of poly(vinylsulfonate) adsorbed on top of polybrene provide a suitable electroosmotic flow at pH 3 without interfering in the retention properties of the microemulsion. For automated measurements the microemulsion run buffer should be replenished after 10 runs to maintain a stable cycle time and the coated columns replaced after 40-70 runs, depending on sample properties.