Chromatography capillary electrokinetic

Several modes of capillary electrophoretic separation are available ordinary CE, capillary zone electrophoresis, capillary electrokinetic chromatography, capillary gel electrophoresis, capillary electrochromatography, capillary isota-chophoresis, and capillary isoelectric focusing. The different separation mechanisms make it possible to separate a wide variety of substances depending on their mass, charge, and chemical nature.53... 

C.C.T. Worth, M. Wiessler and O.J. Schmitz, Analysis of catechins and caffeine in tea extracts by capillary electrokinetic chromatography. Electrophoresis 21 (2000) 3634-3638. 

One of the major advantages of CE as a separation technique is the wide variety of separation modes available. Analytes can be separated on the basis of charge, molecular size or shape, pi, or hydrophobicity. The same CE instrument can be used for zone electrophoresis, IEF, sieving separations, isotachophoresis, and chromatographic techniques such as MEKC and capillary electrokinetic chromatography. This section provides a brief description of each separation mode. Zone electrophoresis, IEF, and sieving are the primary modes used for protein separations, and these will be discussed in detail in the following sections. 

A Amini, C Pettersson, D Westerlund. Enantioresolution of disopyramide by capillary electrokinetic chromatography with human racid glycoprotein (AGP) as chiral selector applying a partial-filling technique. Electrophoresis 18 950-957, 1997. 

Capillary zone electrophoresis (CZE), micellar capillary electrokinetic chromatography (MECC), capillary gel electrophoresis (CGE), and affinity capillary electrophoresis (ACE) are CE modes using continuous electrolyte solution systems. In CZE, the velocity of migration is proportional to the electrophoretic mobilities of the analytes, which depends on their effective charge-to-hydrodynamic radius ratios. CZE appears to be the simplest and, probably, the most commonly employed mode of CE for the separation of amino acids, peptides, and proteins. Nevertheless, the molecular complexity of peptides and proteins and the multifunctional character of amino acids require particular attention in selecting the capillary tube and the composition of the electrolyte solution employed for the separations of these analytes by CZE. 

Capillary electrokinetic chromatography (CEKC) with ESI-MS requires either the use of additives that do not significantly impact the ESI process or a method for their removal prior to the electrospray. Although this problem has not yet been completely solved, recent reports have suggested that considered choices of surfactant type and reduction of electro-osmotic flow (EOF) and surfactant in the capillary can decrease problems. Because most analytes that benefit from the CEKC mode of operation can be effectively addressed by the interface of other separations methods with MS, more emphasis has until now been placed upon interfacing with other CE modes. For small-molecule CE analysis, in which micellar and inclusion complex systems are commonly used, atmospheric pressure chemical ionization (APCI) may provide a useful alternative to ESI, as it is not as greatly affected by involatile salts and additives. 

The first applications of CDs as chiral selectors in CE were reported in capillary isotachophoresis (CITP) [2] and capillary gel electrophoresis (CGE) [3]. Soon thereafter, Fanali described the application of CDs as chiral selectors in free-solution CE [4] and Terabe used the charged CD derivative for enantioseparations in the capillary electrokinetic chromatography (CEKC) mode [5]. It seems important to note that although the experiment in the CITP, CGE, CE, and CEKC is different, the enantiomers in all of these techniques are resolved based on the same (chromatographic) principle, which is a stereoselective distribution of enantiomers between two (pseudo) phases with different mobilities. Thus, enantioseparations in CE are commonly based on an electrophoretic migration principle and on a chromatographic separation principle [6]. 

To date, the use of chemometrics for method development and robustness testing has been published for all areas of CE, including capillary zone electrophoresis (CZE), capillary electrokinetic chromatography (EKC) using chiral selectors for enantioseparations, micellar electrokinetic chromatography (MEKC), and microemulsion electrokinetic chromatography (MEEKC). A comprehensive description can be found in Chapters 5 and 13 as well as in recent reviews (6-11). Several monographs on chemometrics in analytical chemistry have been published such as References 12-14. This chapter will... 

This group includes several related techniques such as classical gel electrophoresis, field-flow fractionation (FFF) and the capillary techniques capillary zone electrophoresis (CZE), capillary electrokinetic chromatography (CEKC) capillary isotachophoresis (CUP), capillary isoelectric focusing (CIEF) and capillary electrochromatography (CEC). 

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

Wei, J., Okerberg, E., Dunlap, J., Ly, C., and Shear, J. B., Determination of biological toxins using capillary electrokinetic chromatography with multiphoton-excited fluorescence. Anal. Chem., 72, 1360, 2000. 

G. Jeevan, M. Bhaskar, R. Chandrasekar and G Radhakrishnan, Separation of harmful chlorophenols by cyclodextrin-assisted capillary electrokinetic chromatography, J. Sep. ScL, 25, 1143-1146, 2002. 

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. 

While the migration principle, i.e., the driving forces moving the analytes through the separation capillary, is based on electrophoretic mechanisms the chiral separation is based on enantioselective interactions between the analyte enantiomers and a chiral selector and is, therefore, a chromatographic separation principle. The fact that the selector is in the same phase as the analytes in CE and not part of a stationary phase that is immiscible with the mobile phase as found in chromatography does not represent a conceptional difference between both techniques. The chiral selector in CE is also called pseudophase as it is not a physically different phase and may also possess an electrophoretic mobility. Enantioseparations in CE have also been termed capillary electrokinetic chromatography . 

This entry summarizes the application of cyclodextrins (CDs) for separation of enantiomers by using capillary electrophoresis (CE) [capillary electrokinetic chromatography (CEKC) and micellar electrokinetic chromatography (MEKC)]. Together with major properties of cyclodextrins as very useful chiral selectors, some mechanistic aspects of enantioseperations by using CE techniques are also emphasized. 

Capillary electrokinetic chromatography (CEKC) with ESI/MS requires either the use of additives that do not significantly impact the ESI process or a method for their... 

K. Bachmann, B. Gdttlicher, 1. Haag, K-Y. Han, W. Hensel, A. Mainka, Capillary electrokinetic chromatography with... 

The stereochemistry of drugs and precursors can be vital in determining synthetic routes. Horvever, since enantiomers are nearly chemically identical, standard chromatographic methods cannot separate them. To effect a chromatographic separation of enantiomers, stereospecific interactions have to be incorporated. As described in Chapter 5, the use of chiral stationary phases is one method of discriminating enantiomers while capillary electrokinetic chromatography (MEKC) using chiral cy-clodextrins is another. Both of these protocols have been applied to methamphetamine and related compounds and precursors, substances that will be discussed in detail later in the chapter. 

AAA absolute activation analysis CEC capillary electrokinetic chromatography,... 

Chiral Recognition and Enantioseparation Mechanisms in Capillary Electrokinetic Chromatography... 

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