Characterization of surfactant and phospholipid vesicles for use as pseudostationary phases in electrokinetic chromatography

Abstract

The physical, electrophoretic and chromatographic properties (mean diameter, electroosmotic flow, electrophoretic mobility, elution range, efficiency, retention, and hydrophobic, shape, and chemical selectivity) of three surfactant vesicles and one phospholipid vesicle were investigated and compared to a conventional micellar pseudostationary phase comprised of sodium dodecyl sulfate (SDS). Chemical selectivity (solute-pseudostationary phase interactions) was discussed from the perspective of linear solvation energy relationship (LSER) analysis. Two of the surfactant vesicles were formulated from nonstoichiometric aqueous mixtures of oppositely charged, single-tailed surfactants, either cetyltrimethylammonium bromide (CTAB) and sodium octyl sulfate (SOS) in a 3:7 mole ratio or octyltrimethylammonium bromide (OTAB) and SDS in a 7:3 mole ratio. The remaining surfactant vesicle was comprised solely of bis(2-ethylhexyl)sodium sulfosuccinate (AOT) in 10% v/v methanol, and the phospholipid vesicle consisted of 1-palmitoyl-2-oleyl-sn-glycero-3-phosphocholine (POPC) and phosphatidyl serine (PS) in 8:2 mole ratio. The mean diameters of the vesicles were 76.3 nm (AOT), 86.9 nm (CTAB/SOS), 90.1 nm (OTAB/SDS), and 108 nm (POPC/PS). Whereas the coefficient of electroosmotic flow (10(-4) cm2 V(-1) s(-1)) varied considerably (1.72 (OTAB/SDS), 3.77 (CTAB/SOS), 4.05 (AOT), 5.26 (POPC/PS), 5.31 (SDS)), the electrophoretic mobility was fairly consistent (-3.33 to -3.87 x 10(-4) cm2 V(-1) s(-1)), except for the OTAB/SDS vesicles (-1.68). This resulted in elution ranges that were slightly to significantly larger than that observed for SDS (3.12): 3.85 (POPC/PS), 8.6 (CTAB/SOS), 10.1 (AOT), 15.2 (OTAB/SDS). Significant differences were also noted in the efficiency (using propiophenone) and hydrophobic selectivity; the plate counts were lower with the OTAB/SDS and POPC/PS vesicles than the other pseudostationary phases (< or = 75,000/m vs. > 105,000/m), and the methylene selectivity was considerably higher with the CTAB/SOS and OTAB/SDS vesicles compared to the others (ca. 3.10 vs. < or = 2.6). In terms of shape selectivity, only the CTAB/SOS vesicles were able to separate all three positional isomers of nitrotoluene with near-baseline resolution. Finally, through LSER analysis, it was determined that the cohesiveness and hydrogen bond acidity of these pseudostationary phases have the greatest effect on solute retention and selectivity.

MEKC: An update focusing on practical aspects

“…Thus, Pascoe and Foley [158] have used this type of vesicle as prepared from nonstoichiometric aqueous mixtures of CTAB and sodium octyl sulfate or octyltrimethylammonium bromide and SDS. In general, all vesicles provided a larger elution range than did SDS micelles, mainly as a result of the high electrophoretic mobility of the vesicles (high charge density) relative to their size.…”

Caracterización estructural de vesículas modificadas con quitosano

“…Se debe indicar que la adsorción del polímero catiónico sobre la bicapa negativamente cargada genera el restablecimiento de la microestructura multilamelar inicial (Hellweg, Brûlet, Lapp, Robertson y Koetz, 2002;Robertson, Hellweg, Tiersch y Koetz, 2004). La preparación de catonosomas, es decir, vesículas constituidas por fosfolípidos y surfactantes catiónicos ha sido reportada por varios estudios (Alves et al, 2007;Kim, Han, Jang y Seong, 2014;Koirala et al, 2016;Pascoe y Foley, 2003). Por ejemplo, Koirala y colaboradores han estudiado el sistema fosfatidilcolina y colesterol en presencia de bromuro de haxadeciltrimetil amonio (CTAB) y bromuro de dihexadeciltrimetil amonio (DHDAB).…”

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

“…As described previously [74], the phase ratio can be accurately calculated from relatively simple relationships based on the total surfactant concentration (C surf ), critical aggregation concentration (CAC), and the partial molar volume(s) of the surfactant(s) V surf À Á . For CTAB/SOS mixtures, the CAC is significantly lower than the CMC of either pure surfactant, and range from 3610 25 to 7610 25 M depending on the mixing ratios [69].…”

“…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].…”

“…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).…”