Effect of class I and II organic modifiers on retention and selectivity in vesicle electrokinetic chromatography

Abstract

Vesicles are large aggregates of surfactant monomers consisting of a spherical bilayer surrounding an internal cavity of solvent. The bilayer structure allows vesicles to be attractive models for the study of various transmembrane and binding processes. The use of thermodynamically stable vesicles (TSV) formed from oppositely charged surfactants for use as a pseudostationary phase in electrokinetic chromatography (EKC) was first accomplished using dodecyltrimethylammonium bromide and sodium dodecyl sulfate (DTAB/SDS). Surfactant vesicles have demonstrated enhanced separation characteristics compared to conventional micelles in EKC, although only investigated in aqueous media. Organic modifiers have been widely studied and used in EKC to enhance separation conditions. In this study, vesicles formed from cetyltrimethylammonium bromide and sodium octyl sulfate (CTAB/SOS) were investigated in the presence of "class I and II" organic modifiers. Electrophoretic and chromatographic parameters were examined as well as linear solvation energy relationship analysis (LSER) to characterize the effects of the modifiers on retention and selectivity in EKC. LSER analysis is a useful way to quantitatively investigate solute/solvent interactions responsible for retention and selectivity.

Hexafluoroisopropanol-modified cetyltrimethylammonium bromide/sodium dodecyl sulfate vesicles as a pseudostationary phase in electrokinetic chromatography

“…Interestingly, the three positional isomers were eluted in the same order (o < p < m) using the two catanionic vesicle systems and two micelle systems, respectively. It was previously reported that p-nitrotoluene was eluted ahead of o-nitrotoluene using series of catanionic surfactant vesicles including DTAB/SDS, CTAB/SOS, OTAB/SDS and C 8 NE 3 Br/SDBS, while o-nitrotoluene was eluted first followed by p-nitrotoluene using the SDS micelles [2,5,7,10,33]. Clearly, the elution order of p-and o-nitrotoluene, obtained using the HFIP-modified and TFE-modified CTAB/SDS vesicles in our present study, was in contrast to that using the catanionic surfactant vesicles described in the above literatures.…”

“…It has been reported that the addition of organic modifiers to a catanionic surfactant vesicles system can exert a significant influence on the electrophoretic parameters of the system [7,8]. In this study, the effect of HFIP on the electrophoretic parameters of a CTAB/SDS vesicle system was investigated in detail and the results are shown in Table 1.…”

“…Since then, mixed surfactant vesicles spontaneously formed from oppositely charged single chain surfactants, also referred to catanionic surfactant vesicles, have attracted increasing attention in EKC. Catanionic surfactant vesicles composed of cetyltrimethylammonium bromide (CTAB) and N-dodecoxycarbonylvaline (DDCV) [3], CTAB and sodium octyl sulfate (SOS) [4][5][6][7][8], octyltrimethylammonium bromide (OTAB) and SDS [5], cetyltrimethylammonium chloride (CTAC) and SOS [8], as well as octyltriethylammoniumbromide (C 8 NE 3 Br) and sodium dodecyl benzene sulfonate (SDBS) [9,10], have been successively examined as PSP in EKC. Compared to micelles, catanionic surfactant vesicles have much larger size, greater surface charge density that allows strong electrostatic interactions, and alternative hydrophobic-hydrophilic discriminatory power provided by the hydrophobic region of the vesicle bilayers [2,5].…”

“…However, to our knowledge, there have been only two reports regarding the use of organic modifiers in the EKC system of catanionic surfactant vesicles. In 2002, Foley research group [7] reported the effect of Class I (1,3-butanediol, 2-amino-1-butanol, 1,2,6-hexanetriol, and glycidol) and Class II (acetonitrile) modifiers on retention and selectivity of the CTAB/SOS vesicles. Later, they further described and compared the effects of 2-amino-1-butanol and acetonitrile on the EOF, elution range, methylene selectivity, and efficiency of the CTAB/SOS vesicles and the CTAC/SOS vesicles [8].…”

Comparison of microstructures of microemulsion and swollen micelle in electrokinetic chromatography

“…It was referred to as solvent modified micelle, or swollen micelle. Recently, 1-butanol modified MEKC was proven to be similar to MEEKC in performance with respect to both separation selectivity and separation efficiency [15][16][17][18][19][20][21]. Wen [22] had compared MEEKC with solvent modified MEKC on rapid separation of heroin, amphetamine and their basic impurities.…”