Electrokinetic Chromatography Using Thermodynamically Stable Vesicles and Mixed Micelles Formed from Oppositely Charged Surfactants

Abstract

The electrokinetic chromatography (EKC) of a novel mixed surfactant system consisting of oppositely charged surfactants, sodium dodecyl sulfate (SDS) and n-dodecyltrimethylammonium bromide (DTAB), was investigated. The chromatographic characteristics of large liposome-like spontaneous vesicles and rodlike mixed micelles formed from the mixture were explored and compared with those of SDS micelles. Separations of a series of n-alkylphenones showed that the spontaneous vesicles provided about a 2 times wider elution window than SDS micelles. Both vesicle and mixed micelle systems were found to provide larger methylene selectivity than SDS. The different elution order of a group of nitrotoluene geometric isomers with DTAB/SDS spontaneous vesicles and SDS micelles pseudostationary phases suggested the possibility of different separation mechanisms with these two systems. Comparisons of polar group selectivity, retention, and efficiency were made between vesicles, mixed micelles, and SDS micelles. The correlation between the logarithms of the retention factors (log k') and octanol-water partition coefficients (log P(ow)) for a group of 20 neutral compounds was also studied with DTAB/SDS vesicles. Spontaneous vesicles have great potential as a pseudostationary phase in electrokinetic chromatography.

Compositional effects on electrophoretic and chromatographic figures of merit in electrokinetic chromatography with cetyltrimethylammonium bromide/sodium octyl sulfate vesicles as the pseudostationary phase. Part 1: Effect of the phase ratio

“…More recently than most of the alternatives to SDS micelles noted above, vesicles formed from phospholipids [43,44] or surfactants [45] were introduced as a PSP for EKC. Compared to micelles, vesicles are much larger aggregates of phospholipid or synthetic surfactant molecules consisting of one or more concentric spherical bilayers ("unilamellar" or "multilamellar") surrounding an internal cavity of solvent.…”

“…The bilayer structure of vesicles resembles that of cell membranes, and although many components of the latter such as peripheral and integral membrane proteins, ionchannels, etc., are typically not included by design in vesicle PSPs for a variety of reasons (increased cost, complexity, lack of commercial availability), both surfactant-and phospholipid-based vesicles have nevertheless proven to be useful for modeling a number of biological and nonbiological processes [50][51][52][53] including the prediction/estimation of drug absorption [54], blood-brain barrier penetration [55], intestinal permeability [56], drug interactions with lipid bilayers [53,57,58], protein-liposome interactions [59], octanolwater partitioning [45,60,61], etc.…”

“…Our research in vesicle EKC (VEKC) has focused, for the most part, on the fundamental electrokinetic and chromatographic properties of catanionic unilamellar vesicles [45,56,60,[71][72][73][74] that in our experience are more easily prepared and more stable than similar aqueous buffered solutions of liposomes [56]. Figures of merit of that have been evaluated include the magnitude of EOF and the electrophoretic mobility of the vesicle, efficiency (plate count), retention, selectivity (methylene, shape, enantioselectivity, and/or chemical (LSER), and the elution range (migration window).…”

“…Figures of merit of that have been evaluated include the magnitude of EOF and the electrophoretic mobility of the vesicle, efficiency (plate count), retention, selectivity (methylene, shape, enantioselectivity, and/or chemical (LSER), and the elution range (migration window). Besides unilamellar surfactant vesicles comprised of CTAB/SOS [56,60,72,73], we have examined vesicles consisting of DTAB/ SDS [45], dodecoxycarbonylvaline (DDCV)/SDS [71], octyltrimethylammonium bromide (OTAB)/SDS [74], and cetyltrimethylammonium chloride (CTAC)/SOS [73].…”

Application of Retention Factors in Affinity Electrokinetic Chromatography and Capillary Electrophoresis

“…Various means for obtaining the partial molar volume of the additive as well as the critical aggregation concentration have been applied, 13,[19][20][21][22][23] and references cited therein. It is evident from above that the retention factor is instrumental for determining the distribution coefficient.…”