Electrokinetic chromatography pseudostationary phase

The effects of pH on electrokinetic velocities in micellar electrokinetic chromatography was studied by using sodium dodecyl sulfate solutions [179]. Micellar electrokinetic capillary chromatography with a sodium dodecyl sulfate pseudostationary phase has been used to determine the partition constants for nitrophenols, thiazolylazo dyes, and metal chelate compounds [180]. A similar technique was used to separate hydroquinone and some of its ether derivatives. This analysis is suitable for the determination of hydroquinone in skin-toning creams [181]. The ingredients of antipyretic analgesic preparations have also been determined by this technique [182], The addition of sodium dodecyl sulfate improves the peak shapes and resolution in chiral separations by micellar electrokinetic chromatography [183]. 

S. L, Carlucci, A., Bregni, C., Kenndler, E. Comparison of the retention charaderi sties of different pseudostationary phases for microemulsion and micellar electrokinetic chromatography of betamethasone and derivatives. Electrophoresis 2003, 24, 984-991. 

Electrokinetic chromatography (EKC) using microemulsion is one of the most powerful tools for the rapid measurement of log P w with high reproducibility. Because it is relatively easy to manipulate the pseudostationary phases of EKC, a lot of phases have been reported for the measurement not only of physicochemical properties but also of the separation selectivity, such as polymer micelles (64) and double-chain surfactant vesicles (56-58,60,61). These phases are also interesting in terms of the correlation to bioactivity. 

C Fujimoto. Application of linear solvation energy relationships to polymeric pseudostationary phases in micellar electrokinetic chromatography. Electrophoresis 22 1322-1329 (2001). 

K Bachmann, A Bazzanella, I Haag, K-Y Han. Charged native -cyclodextrin as a pseudostationary phase in electrokinetic chromatography. Fresenius J Anal Chem 357 32-36, 1997. 

S Terabe, H Ozaki, Y Tanaka. New pseudostationary phases for electrokinetic chromatography A high-molecular surfactant and proteins. J Chin Chem Soc 41 251-257, 1994. 

Electrokinetic chromatography (EKC) comprises a variety of electromigration techniques that use electrolyte solutions incorporating a separation carrier, which is called the pseudostationary phase, and are based on the distribution of the analytes between this phase and the surrounding solution. 

Micellar electrokinetic chromatography is a form of chromatography because the micelles behave as a pseudostationary phase. Separation of neutral molecules is based on partitioning between the solution and the pseudostationary phase. The mass transfer term Cux is no longer 0 in the van Deemter equation 26-7, but mass transfer into the micelles is fairly fast and band broadening is modest. 

Wang, H. et al.Sodium maleopimaric add as pseudostationary phase for chiral separations of amino acid derivatives by capillary micellar electrokinetic chromatography. J. Sep. Sci. 2007, 30, 2748-2753. 

The phenomena just described are quite similar to what occurs in a liquid partition chromatographic column except that the stationary phase is moving along the length of the column at a much slower rate than the mobile phase. The mechanism of separations is identical in the two cases and depends on differences in distribution constants for analytes between the mobile aqueous phase the hydrocarbon pseudostationary phase. The process is thus true chromatography hence, the name micellar electrokinetic capillary chromatography. Figure 33-15 illustrates two typical separations by MECC. 

There are numerous variations on free solution CE (FSCE), such as micellar electrokinetic capillary chromatography (MECC or MEKC), where a moving, pseudostationary phase is added to the CE buffer, and secondary chemical equilibria or interactions ensue that effect separations of even neutral compounds, as well as ionic analytes. However, in general, CE utilizes truly homogeneous, solution phase separation approaches, without a stationary (permanent, fixed) phase, making it perhaps ideally suited for molecular recognition in searching combinatorial libraries. 

A recently proposed method (314) for the separation of fat-soluble vitamins by electrokinetic chromatography was further developed (315). The separation medium consisted of acetonitrile water (80 20 v/v) and contained tetradecylam-monium bromide as a pseudostationary phase. The high acetonitrile content was necessary to keep the hydrophobic vitamins in solution during electrophoresis. With the cathode placed at the capillary outlet, the fat-soluble vitamins were separated based on different hydrophobic interactions with the pseudo-stationary phase. The vitamins migrated in order of decreasing hydrophobicity prior to the electroosmotic flow. 

O Naess, T Tilander, S Pedersen-Bjergaard, KE Rasmussen. Analysis of vitamin formulations by electrokinetic chromatography utilizing tetradecylammonium ions as the pseudostationary phase. Electrophoresis 19 2912-2917, 1998. 

The apparent electrophoretic mobility of an analyte in micellar electrokinetic chromatography depends on three factors the electroosmotic mobility for the system the fraction of analyte in the electrolyte solution and its electrophoretic mobility and the fraction of analyte in the pseudostationary phase, and the electrophoretic mobility of the micelles (assuming that the mobility of the analyte-micelle complex is the same as the micelle). If we introduce the chromatographic retention factor, defined as the ratio of the number of analyte molecules in the pseudostationary phase to the number in the... 

Polymeric micelles form stable pseudostationary phases with a critical micelle concentration of virtually zero (aggregation number of 1), and are tolerant of high organic solvent concentrations in the electrolyte solution. Mass transfer kinetics are slow compared with conventional surfactant micelles, and peak distortion from mass overloading is a problem for some polymer compositions. Preliminary studies indicate that polymeric surfactants are effective pseudostationary phases in micellar electrokinetic chromatography, but only a limited number of practical applications have been demonstrated, and uptake has been slow. 

Explain how micellar electrokinetic chromatography combines electrophoretic and chromatographic separation principles. Why is the MEKC micelle called a pseudostationary phase ... 

Maichel B, Kenndler E. Recent iimovation in capillary electrokinetic chromatography with replaceable charged pseudostationary phases or additives. Electrophoresis 2000 21 3160-73. 

Minimizing the temperature effects discussed above could be obtained with the use of polymer micelles or polymer surfactants [81-83], whose CMC is zero, and even in nonaqueous solvent, the micelle is stable. Although several polymer surfactants are commercially available, no such surfactant is widely accepted, probably because SDS, CTAB, or CTAC, and bile salts are superior to polymer surfactants as the pseudostationary phase in MEKC. Although microemulsion electrokinetic chromatography (MEEKC) is not discussed in this chapter but covered in Chapter 4 by Altria and colleagues, a similar optimization strategy to that in MEKC applies to MEEKC [84-86]. Since... 

Muijselaar, R.G., Claessens, H.A., and Cramers, C.A., Characterization of pseudostationary phases in micellar electrokinetic chromatography by applying linear solvation energy relationships and retention indexes, AnaZ. Chem., 69,1184,1997. 

Palmer, C.P. and McCarney, J.P., Recent progress in the use of soluble ionic polymers as pseudostationary phases for electrokinetic chromatography. Electrophoresis, 25, 4086, 2004. 

D.S. Peterson and C.P. Pahner, An anionic siloxane polymer as a pseudostationary phase for electrokinetic chromatography. Electrophoresis, 21, 3174-3180, 2000. 

S.H. Edwards and SA. Shamsi, Micellar electrokinetic chromatography of polychlorinated biphenyl congeners using apolymeric surfactant as the pseudostationary phase, J. Chromatogr. A, 903,227-236,... 

A.L. Gray and J.T. Hsu, Novel sulfonic acid-modified Starburst dendrimer used as a pseudostationary phase in electrokinetic chromatography, J. Chromatogr. A, 824, 119-124, 1998. 

B. Maichel, B. Potocek, B. Gas and E. Kenndler, Capillary electrokinetic chromatography with polyethyleneimine as replaceable cationic pseudostationary phase. Influence of methanol and acetonitrile on separation selectivity, J. Chromatogr. A, 853, 121-129, 1999. 

A. Bazzanella, H. Morbel, K. Bachmann, R. MUbradt, V. Bohmer and W. Vogt, Highly efficient separation of amines by electrokinetic chromatography using resorcarene-octacarboxylic acids as pseudostationary phases,/. Chromatogr. A, 191, 143-149, 1997. 

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