Micellar electrokinetic chromatography surfactants used

C.-E. Lin, Y.-T. Chen and T.-Z. Wang, Separation of benzenediamines, benzenediols and aminophenols in oxidative hair dyes by micellar electrokinetic chromatography using cationic surfactants. J. Chromatogr.A, 837 (1999) 241-252. 

Til. Ozaki, H., Itou, N., Terabe, S., Takada, Y., Sakairi, M., and Koizumi, H. (1995). Micellar electrokinetic chromatography mass-spectrometry using a high-molecular-mass surfactant - online coupling with an electrospray-ionization interface.. Chromatogr. A 716, 69—79. 

Shamsi, S. A. (2001). Micellar electrokinetic chromatography-mass spectrometry using a polymerized chiral surfactant. Anal. Chem. 73, 5103-5108. 

Micellar electrokinetic chromatography is a hybrid of electrophoresis and chromatography. Introduced by Terabe in 1984 (9), MEKC is one of the most widely used CE modes. Ionic micelles, formed from surfactants added... 

Figure 26-33 Separation of enantiomers of eight p blocker drugs by micellar electrokinetic chromatography at pH 8.0 in a 120-cm capillary at 30 kV. Micelles were formed by a polymer surfactant containing L-leucinate substituents for chiral recognition. The structure of one compound is shown. [From C. Akbay. S, A. A. Rizvi. and S. A. Shamsi, "Simultaneous Enantiosepcration and Tandem UV-MS Detection of Eight p-Blockers in Micellar Electrokinetic Chromatography Using a Chiral Molecular Micelle Anal. Chem. 2005, 77.1672.]...

Micellar electrokinetic chromatography (MEKC) is a modality of liquid chromatography having a surfactant molecule in the form of a micelle, which was introduced by Terabe et al. in 1984 [38]. The formation and separation occur in the capillary and, hence, it is also called micellar electrokinetic capillary chromatography (MECC). This modality is useful for some specific molecules having solubilities in micelles and, therefore, utilized for the separation and identification of such compounds with great efficiency, reproducibility, and low levels of detections. The most commonly used compounds for micelle formation are sodium dodecyl sulfate (SDS), sodium tetradecyl sulfate, sodium decanesulfonate, sodium /V-lauryl-/V-mcthyllauratc, sodium... 

Mwongela, S.M., Numan, A., Gill, N.L., Agbaria, R.A., and Warner, I.M. 2003. Separation of achiral and chiral analytes using polymeric surfactants with ionic liquids as modifiers in micellar electrokinetic chromatography. Analytical Chemistry, 75 6089-96. 

Conceptually. CE enantioseparations are mainly applied to charged SAs. Micellar electrokinetic chromatography (MEKC) (introduced by Terabe et al. in 1984 488 ), in contrast, permits the separation of electrically neutral compounds. In enantiomer separation by MEKC. ionic pseudo-stationary phases, such as chiral micelles composed of chiral SO moieties, which migrate according to their electrophoretic mobility, may interact stereoselectively with the solutes to be separated. MEKC with synthetic (e.g. A-dodecoxycarbonylvalines, commercialized as SDVal by Waters) 1489.490) or naturally occurring chiral surfactants (e.g. bile salts) 1491-494). and cyclodextrin-moditied MEKC (most often SDS/CD combinations) 1495-498) are the mo.st widely used selector systems in MEKC. The topic of MEKC enantioseparation has been reviewed by Nishi )499). 

Otsuka, K. and S. Terabe, Micellar electrokinetic chromatography, Bull. Chem. Soc. Jpn. 71 2465 (1998). Otsuka, K. and S. Terabe, Enantiomer separation of drugs by micellar electrokinetic chromatography using chiral surfactants, /. Chromatogr. A 875 163 (2000). 

The technique is therefore particularly suited to water-soluble species which possess a charge, which includes most dyes. Variations from the main technique (often referred to as capillary zone electrophoresis, CZE) do exist and these include the use of surfactants in the buffer to create micelles (often thought of as creating a pseudo-stationary phase inside the capillary) which then improve the separation of neutral species (and frequently charged molecules) owing to hydrophobic interactions. The term micellar electrokinetic chromatography (MECC or MEKC) is often used for CE separations carried out with the aid of a micellar buffer solution. 

Another modification of CE is micellar electrokinetic chromatography (MEKC), which is widely used for the separation of nonpolar compounds. The molecules in question partition into micelles (nonpolar layer) with mechanisms similar to those observed with reverse-phase chromatography. An anionic surfactant, sodium dodecyl sulfate, is commonly used as a micellar... 

K Otsuka, S Terabe. Enantiomer separation of drugs by micellar electrokinetic chromatography using chiral surfactants. J Chromatogr A 875 163-178, 2000. 

Capillary electrophoresis (CE) has emerged as an efficient and rapid separation technique in recent years. Its high efficiency has been employed in many applications such as in the analysis of environmental pollutants.Different approaches have been adopted to enhance selectivity for the analysis of different types of compounds. There are two approaches most commonly used to improve CE separations the addition of modifiers into the electrophoretic medium and the modification of the column. Examples of the first approach include the addition of surfactants into the electrophoretic medium as in micellar electrokinetic chromatography (MEKC), and the use of organic solvents,cyclodextrines, " " or bile salts " as buffer modifiers. Examples of the second method include the use of gel-filled columns (capillary gel electrophoresis) " and the coating of the capillary wall surface. " " ... 

Monomeric nucleosides and nucleotides, which appear as impurities in oligonucleotide synthesis, may be analyzed using the method of micellar electrokinetic chromatography (MEKC). With addition of SDS to the buffer solution, the surfactant concentration is above the critical micellar concentration. Movement of the micelles towards the anode against the EOF involves distribution processes, in which also nucleosides, nucleobases and nucleotides participate. Typical conditions are 50 mM phosphate buffer 40 mM SDS pH 6.5 20 kV (116 mA) 21 °C [186]. 

Neutral cyclodextrins are also used in micellar electrokinetic chromatography with achiral surfactants to modify their enantioselectivity, particularly for the separation of hydrophobic analytes [53,55,185-187]. Enantioselectivity in this case results from differences in the distribution of enantiomers between the micellar pseudostation-ary phase and the cyclodextrin, as well as from the different migration velocities of the cyclodextrin and micelles. Neutral enantiomers can be separated based on differences in their equilibrium constants between the electrolyte solution and a charged chiral surfactant micellar phase, if the micelle has a different electrophoretic mobility to the free enantiomers. Suitable chiral surfactants include the bile salts (section 8.3.3), long alkyl-chain amino acid derivatives (e.g. sodium N-dodecanoyl-... 

As detailed in Chapter 3 by Terabe, micellar electrokinetic chromatography (MEKC) is a useful technique in the retention analysis of water-soluble compounds. The separation and analysis of lypophilic analytes, however, may be difficult in MEKC due to the strong affinity of lypophilic compounds to the micelle resulting in long separation times and poor resolution. An interesting approach for the simultaneous analysis of water- and fat-soluble vitamins by microemulsion electrokinetic chromatography (MEEKC) was proposed by Sanchez. The separation of both water- and fat-soluble vitamins (Bi, B2, B3, Be, B12, C, A palmitate, D, E acetate, and K) was obtained when the microemulsion was prepared with sodium dodecyl sulfate (SDS) as the surfactant, octane as the nonpolar modifier, butanol as the cosurfactant, and propanol as the second cosurfactant. Complete separation of all vitamins was carried out within 55 min however, this approach was tested only in multivitamin formulation. 

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,... 

Micellar electrokinetic chromatography uses ionic surfactants at a concentration above the critical micelle concentration (CMC) as a component of the run buffer chosen to separate compounds. This generates a pseudo-stationary phase that performs the separation. This technique is therefore optimal for separating neutral and charged compounds from each other. In addition compounds that are very hydrophobic, and those typically insoluble in traditional capillary electrophoresis run separate buffers under these conditions. Neutral compounds elute in the order of their hydrophobicity. 

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