Capillary electrokinetics

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. 

Altria, K. D., and Rogan, M. M. (1990). Reductions in sample pretreatment requirements by using high-performance capillary electrokinetic separation methods. J. Pharm. Biomed. Anal. 8, 1005-1008. 

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. 

Abstract Investigations of alternate adsorption regularities of cationic polyelectrolytes a) copolymer of styrene and dimethylaminopropyl-maleimide (CSDAPM) and b) poly(diallyldimethylammonium chloride) (PDADMAC) and anionic surfactant - sodium dodecyl sulfate (SDS) on fused quartz surface were carried out by capillary electrokinetic method. The adsorption/desorption kinetics, structure and properties of adsorbed layers for both polyelectrolytes and also for the second adsorbed layer were studied in dependence on different conditions molecular weight of polyelectrolyte, surfactant and polyelectrolyte concentration, the solution flow rate through the capillary during the adsorption, adsorbed layer formation... 

In this paper we investigate the process of alternate adsorption of cationic polyelectrolyte and anionic surfactant, structure and properties of adsorbed layers depending on different factors (molecular weight of PE, concentration of polyelectrolyte and surfactant, adsorbed layer formation time, the flow rate of the solution) by measuring potential and streaming current using the capillary electrokinetic method. 

Electrokinetic measurements. In this study the capillary electrokinetic method was applied [16],... 

The capillary electrokinetic method allows to get the information about the structure of the adsorbed layers by measuring the dependence of f potential on the pressure enclosed (AP) (Figs. 6 and 7). 

Luong JHT, Guo Y. Mixed-mode capillary electrokinetic separation of positional explosive isomers using sodium dodecyl sulfate and negative-P-cyclodextrin derivatives. J Chromatogr A 1998 811 225. 

D.W. Armstrong, G. Schulte, J.M. Schneiderheinze and D.J. Westenberg, Separating microbes in the manner of molecules. 1. Capillary electrokinetic approaches, A7iaZ. Chem., 71 (1999) 5465-5469. 

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]. 

The separation capillary is prepared by polymerizing 6%T, 5%C monomers with 30% formamide and 7 M urea inside a 37 cm long, 50 pm i.d. fused silica capillary. Electrokinetic injection at 200 V/cm for 30 s was used, since hydrodynamic injection does not work with gel-filled capillaries. Separation on the gel occurs by seiv-ing, so that the shortest fragments elute first. Figure 12.12 shows the data obtained using a TAMRA dye label that is excited at 543.5 nm and emits at 590 nm. This method has a detection limit of 2 zmol (1 zmol = 10 21 mol) for each fragment. 

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. 

Hilhorst M.J., Somsen GW., de Jong G.J., Capillary electrokinetic separation techniques for profiling of drugs and related products. Electrophoresis, 22, 2542-2564 (2001). 

Whitaker, K.W. and Sepaniak, M.J., Nonaqueous packed capillary electrokinetic chromatographic separations of large polycyclic aromatic hydrocarbons and fullerenes, Electrophoresis, 15, 1341, 1994. 

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.K. Belin, E.B. Erim and F. Gulacar, Capillary electrokinetic separation of polycyclic aromatic hydrocarbons nsing cetylpyridinium bromide. Polycyclic Atom. Compds., 24, 343-352, 2004. 

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. 

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