Indirect determination of octanol-water partition coefficients by microemulsion electrokinetic chromatography

Microemulsion electrokinetic chromatography (MEEKC) was assessed and developed as a screening tool for the indirect determination of octanol-water partition coefficients. The capacity factors from MEEKC were correlated to the octanol-water partition coefficients. The same microemulsion (50 mM SDS, 400 mM butanol and 32 mM heptane) was used at pH 1.19 and pH 12 allowing most compounds to be run in their neutral state. This procedure was evaluated using a set of 24 structurally diverse solutes and 4 homologs. It was found that MEEKC can determine a range of over 5 orders of magnitude in the log K-ow covering from -1 to over 4. MEEKC provides all the advantages of an HPLC system to estimate lipophilicities including automation, small sample size, short run and analysis times and good reproducibility. However, MEEKC has neither the disadvantages of HPLC including pH limitations, column degradation and homologous series limitations nor the disadvantages of shake flask methods including large sample size, no automation and long turnaround.