Correlation of the capacity factor in vesicular electrokinetic chromatography with the octanol:water partition coefficient for charged and neutral analytes.
OBJECTIVE
The aim of this study was to develop a method based upon electrokinetic chromatography (EKC) using oppositely charged surfactant vesicles as a buffer modifier to estimate hydrophobicity (log P) for a range of neutral and charged compounds.


METHODS
Vesicles were formed from cetyltrimethylammonium bromide (CTAB) and sodium n-octyl sulfate (SOS). The size and polydispersity of the vesicles were characterized by electron microscopy, dynamic light scattering, and pulsed-field gradient NMR (PFG-NMR). PFG-NMR was also used to determine if ion-pairing between cationic analytes and free SOS monomer occurred. The CTAB/SOS vesicles were used as a buffer modifier in capillary electrophoresis (CE). The capacity factor (log k') was calculated by determining the mobility of the analytes both in the presence and absence of vesicles. Log k' was determined for 29 neutral and charged analytes. RESULTS; There was a linear relationship between the log of capacity factor (log k') and octanol/water partition coefficient (log P) for both neutral and basic species at pH 6.0, 7.3, and 10.2. This indicated that interaction between the cation and vesicle was dominated by hydrophobic forces. At pH 4.3, the log k' values for the least hydrophobic basic analytes were higher than expected, indicating that electrostatic attraction as well as hydrophobic forces contributed to the overall interaction between the cation and vesicle. Anionic compounds could not be evaluated using this system.


CONCLUSIONS
Vesicular electrokinetic chromatography (VEKC) using surfactant vesicles as buffer modifiers is a promising method for the estimation of hydrophobicity.
Razak
J L
JL
Department of Chemistry, University of Kansas, Lawrence 66045, USA.
Cutak
B J
BJ
Larive
C K
CK
Lunte
C E
CE
D017738:Alkanesulfonic Acids / Q000737:chemistry*; D000779:Anesthetics, Local / Q000737:chemistry*; D002214:Capsules; D000077286:Cetrimonium; D002593:Cetrimonium Compounds / Q000737:chemistry*; D020374:Chromatography, Micellar Electrokinetic Capillary / Q000379:methods*; D019075:Electrophoresis, Capillary / Q000379:methods; D008854:Microscopy, Electron; D000442:Octanols / Q000737:chemistry; D013501:Surface-Active Agents / Q000737:chemistry*; D014867:Water / Q000737:chemistry
D017738:Alkanesulfonic Acids; D000779:Anesthetics, Local; D002214:Capsules; D002593:Cetrimonium Compounds; D000442:Octanols; D013501:Surface-Active Agents; D014867:Water; C042005:1-octanesulfonic acid; D000077286:Cetrimonium