Pseudostationary Phases In Micellar Electrokinetic Chromatography Research Articles

Binary mixed micelles of chiral sodium undecenyl leucinate and achiral sodium undecenyl sulfate: I. Characterization and application as pseudostationary phases in micellar electrokinetic chromatography

Sodium 10-undecenyl sulfate (SUS), sodium 10-undecenyl leucinate (SUL) and their five different mixed micelles at varied percent mole ratios were prepared. The critical micelle concentration (CMC), C 20, γ CMC, partial specific volume, methylene group selectivity, mobilities and elution window were determined using a variety of analytical techniques. These surfactant systems were then evaluated as novel pseudostationary phases in micellar electrokinetic chromatography (MEKC). As a commonly used pseudostationary phase in MEKC, sodium dodecyl sulfate (SDS) was also evaluated. The CMC values of SUS and SUL were found to be 26 and 16 mM, respectively, whereas the CMC of mixed surfactants was found to be very similar to that of SUL. The C 20 values decreased dramatically as the concentration of SUL is increased in the mixed micelle. An increase in SUL content gradually increased the methylene group selectivity making the binary mixed surfactants more hydrophobic. Linear solvation energy relationships (LSERs) and free energy of transfer studies were also applied to predict the selectivity differences between the surfactant systems. The cohesiveness and the hydrogen bond acidic character of the surfactant systems were found to have the most significant influence on selectivity and MEKC retention. The SUS and SDS showed the strongest while SUL showed the weakest hydrogen bond donating capacity. The basicity, interaction with n and π-electrons of the solute and dipolarity/polarizability were the least significant factors in LSER model for the surfactant systems studied. Free energies of transfer of selected functional groups in each surfactant systems were also calculated and found to be in good agreement with the LSER data.

Application of Protein-Liposome Conjugate as a Pseudo-Stationary Phase in Capillary Electrophoresis

Liposomes have very similar structure to cell plasma membranes. Using liposomes as stationary phase in liquid chromatography (LC) or micellar electrokinetic chromatography (MEKC) has been demonstrated to be a good, dynamic method for the study of the interaction between cell membranes and important biomolecules. There has been no report on integrating plasma membrane proteins with phospholipids as pseudo-stationary phase in MEKC. In this paper, a novel mode of capillary electrophoresis (CE) is developed, that is, protein-liposome conjugate. This protein-liposome biomimetic membrane is demonstrated for the first time to be applicable as pseudo-stationary phase in MEKC. The protein is able to significantly improve chromatographic performance and stability. The experimental phenomena are further confirmed in terms of specific capacity factors and free binding energy. This new CE mode is used to investigate the interaction between dopamine transporter and dopamine-nomifensine.

Novel anionic copolymerized surfactants of mixed achiral and chiral surfactants as pseudostationary phases for micellar electrokinetic chromatography.

One disadvantage of amino acid-based chiral selectors for micellar electrokinetic chromatography (MEKC) is that either they have very low solubility or are insoluble at acidic pHs. In order to increase solubilities at lower pHs, we have synthesized a highly water-soluble achiral surfactant and copolymerized it with an amino acid-based chiral surfactant. These two surfactants were polymerized either separately or at various molar rations of binary solutions, yielding pure molecular or copolymerized surfactant (CoPS), respectively. All surfactants were characterized by use of several analytical techniques prior to using them as novel pseudostationary phases in MEKC. The chromatographic performance of the CoPS in MEKC was tested with chiral and achiral analytes. The highly soluble sulfate head group significantly increased the solubility of amino acid-based CoPS over a wide range of pH. Three chiral binaphthyl derivatives were tested and each surfactant system was found to have different selectivity.

Application of polyelectrolyte complexes as novel pseudo-stationary phases in MEKC.

Polyacrylic acid (PAA) and polymethacrylic acid (PMAA) with carboxyl groups partially blocked by dodecyltrimethylammonium bromide (DTAB) and tetrabutylammonium bromide (TBAB) were tested as new pseudo-stationary phases in micellar electrokinetic chromatography (MEKC). The separation of was examined using PAA and PMAA. Excellent resolution of the substituted phenols and derivatized amino acids was demonstrated using additives of PAA-DTAB polyelectrolyte complex in the running phosphate buffer. It was found that the capacity factors were proportional to the concentration of the complex PAA/DTAB. Critical micelle concentration was effectively zero. It was found that the migration times and efficiency of separation of phenols and derivatives of amino acids depended on the type of polymers and alkyltrimethylammonium salts used.

On-line sample concentration in micellar electrokinetic chromatography with cationic micelles in a coated capillary

The electroosmotic flow was successfully suppressed even in the presence of cationic surfactants, when a polyacrylamide-coated capillary was employed. Two on-line sample concentration techniques of sample stacking and sweeping were evaluated in micellar electrokinetic chromatography (MEKC) using the polyacrylamide-coated capillary. Cationic surfactants were used as pseudostationary phases in MEKC. At least 60-fold and about 600-fold increases in detection sensitivity were obtained in terms of peak heights by sample stacking and sweeping, respectively.

Effect of the polar groups of anionic surfactant on migration behavior in micellar electrokinetic chromatography

Three kinds of anionic surfactants with different polar groups were used as the pseudo-stationary phase in micellar electrokinetic chromatography (MEKC). We found that sodium N-lauroyl-N-methyl-β-alaninate (ALE) can be used as a pseudo-stationary phase in MEKC, as well as sodium N-lauroyl-N-methyltaurate (LMT) and sodium dodecyl sulfate (SDS). The ionic groups are carboxylate, sulfonate and sulfate, respectively. ALE and LMT have amido linkages. The migration behavior of aniline derivatives and phenol derivatives was investigated with these surfactants. The difference in the migration behavior was compared in terms of the capacity factor. Surfactants with amido linkages showed different selectivity from SDS, for phenol derivatives. The three surfactants also gave different selectivity for aniline derivatives. Changing the buffer pH affected greater the migration behavior of aniline derivatives with SDS than those with ALE and LMT. The correlation of the capacity factor and the octanol-water partition coefficient for each solute was also investigated. Correlation with ALE was the highest among the three surfactants.

Characterization of Pseudostationary Phases in Micellar Electrokinetic Chromatography by Applying Linear Solvation Energy Relationships and Retention Indexes

The influence of different solute−micelle interactions on micellar solubilization is studied by using linear solvation energy relationship (LSER) modeling. The LSER results for six anionic micellar systems demonstrate that the migration behavior of neutral species in micellar electrokinetic chromatography (MEKC) is mainly determined by their molar volume and their hydrogen bond acceptor ability. Their polarity and hydrogen bond donor ability are shown to be of minor importance with these anionic surfactants. Large differences in selectivity were observed for sodium dodecyl sulfate (SDS) and mixed SDS/Brij 35 micellar systems, primarily due to different hydrogen bonding characteristics. It is demonstrated that retention indexes can be applied for quantitative characterization of pseudostationary phases in MEKC in a way similar to the use of the Rohrschneider−McReynolds scale in GC. This method facilitates classification of pseudostationary phases according to several solvatochromic quantities with a limite...