HYDROPHOBICITY OF CATIONIC SOLUTES MEASURED BY ELECTROKINETIC CHROMATOGRAPHY WITH CATIONIC MICROEMULSIONS

The effect of the structure of employed surfactants on the selectivity of microemulsion electrokinetic chromatography (MEEKC) was investigat ed. Both their ionic groups and their hydrocarbon chain lengths did no t affect the selectivity for neutral solutes. However, for cationic so lutes, ionic interactions between cationic solutes and anionic surfact ants both in the aqueous phase and in the microemulsion phase were obs erved. Based on these results, determination of the hydrophobicity of cationic solutes was done using MEEKC with cationic microemulsions. Th e obtained migration index (MI), which had been proposed as a novel hy drophobicity scale measured by MEEKC (Ishihama, Y.; et al. Anal. Chem. 1995, 67, 1588), correlated with conventional hydrophobicity scales f or a water/1-octanol system, a liposome system, and an HPLC system usi ng a phospholipid-immobilized artificial membrane (IAM) column. Quanti tative structure-activity relationship studies on a protein binding af finity using MI as well as the hydrophobicity scales using the liposom e and the IAM column provided better results than those using the wate r/1-octanol system.