Capillary electrophoresis resolution mechanisms

Enantioresolution in capillary electrophoresis (CE) is typically achieved with the help of chiral additives dissolved in the background electrolyte. A number of low as well as high molecular weight compounds such as proteins, antibiotics, crown ethers, and cyclodextrins have already been tested and optimized. Since the mechanism of retention and resolution remains ambiguous, the selection of an additive best suited for the specific separation relies on the one-at-a-time testing of each individual compound, a tedious process at best. Obviously, the use of a mixed library of chiral additives combined with an efficient deconvolution strategy has the potential to accelerate this selection. 

Instrumental resolution, 23 132 Instrumentation. See also Instruments calibration of, 21 161 capillary electrophoresis, 4 633 composition measurement, 11 785 for fermentation, 11 36—40 flow rate, 11 781-783 flow visualization, 11 785-786 fluid mechanics, 11 781-786 food processing, 12 87-88 gas chromatography, 4 611 6 413-414 infrared spectroscopy, 14 225-228 23 137-138... 

Capillary electrophoresis provides unprecedented resolution. When we conduct chromatography in a packed column, peaks are broadened by three mechanisms in the van Deemter equation (23-33) multiple flow paths, longitudinal diffusion, and finite rate of mass transfer. An open tubular column eliminates multiple paths and thereby reduces plate height and improves resolution. Capillary electrophoresis reduces plate height further by knocking out the mass transfer term that comes from the finite time needed for solute to equilibrate... 

Micellar electrokinetic capillary chromatography (MECC) is a mode of CE similar to CZE, in which surfactants (micelles) are added to the buffer system. Micellar solutions can be used to solubilize hydrophobic compounds that would otherwise be insoluble in water. In MECC the micelles are used to provide a reversed-phase character to the separation mechanism. Although MECC was originally developed for the separation of neutral species by capillary electrophoresis, it has also been shown to enhance resolution in the analysis of a variety of charged species.16... 

The fundamental separation mechanism of capillary zone electrophoresis (CZE) is based on differences in the mobilities of solutes. Mobility is defined as the charge/mass ratio for each solute. Since the charge is often a function of pH, the pH is the most important adjustable parameter for control of resolution. The order of elution on bare silica at high pH is cations, unseparated neutrals, and anions. At low pH, where the EOF is very low, the anions may migrate toward the positive electrode and may not be seen using normal polarity. 

Since selectivity is a prerequisite for resolution, a temperature increase strongly impacts both selectivity and resolution. The variability of the van t Hoff lines explains the seemingly erratic result of the influence of tanperature on the figures of merit of the method. For example, at lower temperatures, the resolution of model peptides with +1 and +3 net charges improved and worsened, respectively [27]. In chiral IPC, T < 0°C was successfully used to improve enantioresolution [28]. Similarly, lower temperatures provided better resolution in the analysis of a new aminoglycoside antibiotic [29] and for characterization of maize products [30]. Conversely, an increased resolution at 70°C was observed when the ion-pair mechanism was exploited under IPC-capillary zone electrophoresis of cationic proteomic peptide standards [31]. 

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