Zone selection, capillary

Catechin and epicatechin are two flavanols of the catechin family. They are enantiomers. The capillary zone electrophoresis (CE) methods with UV-detection were developed for quantitative determination of this flavanols in green tea extracts. For this purpose following conditions were varied mnning buffers, pH and concentration of chiral additive (P-cyclodextrin was chosen as a chiral selector). Borate buffers improve selectivity of separation because borate can make complexes with ortho-dihydroxy groups on the flavanoid nucleus. 

S. Palmarsdottir and L. E. Edholm, Enhancement of selectivity and concentration sensitivity in capillary zone electrophoresis by on-line coupling with column liquid chromatography and utilizing a double stacking procedure allowing for microliter injections , 7. Chromatogr. 693 131-143 (1995). 

Qualitatively equation (7.15) is adequate to describe tiM f influence of layer quality, selectivity, and zone position in the 1 chromatogram upon resolution for a single unidimensional development under capillary flow controlled conditions. The variation of R, with Rf is not a simple function as can be seen from Figure 7.6. The resolution increases with the layer efficiency in a manner that depends linearly on the R, value. — Relatively small changes in selectivity have an enormous impact on... 

Grossman, R D., Wilson, K. J., Petrie, G., and Lauer, H. H., Effect of buffer pH and peptide composition on the selectivity of peptide separations by capillary zone electrophoresis, Anal. Biochem., 173, 265, 1988. 

Y. An, J. W. Cooper, B. M. Balgley, and C. S. Lee. Selective Enrichment and Ultrasensitive Identification of Trace Peptides in Proteome Analysis Using Transient Capillary Isotachophoresis/Zone Electrophoresis Coupled with Nano-ESI-MS. Electrophoresis, 27(2006) 3599-3608. 

Surfactants are selected based primarily on the degree of solubilization. Other factors to be considered include toxicity, biodegradability, surfactant sorption, and surfactant solubility and compatibility with the separation process. Surfactants have the ability to lower the interfacial tension between water and the contaminant by as little as a factor of three to four orders of magnitude. Combined with a sufficient reduction in capillary forces, this allows pumped groundwater theoretically to move the DNAPL toward the recovery or extraction well. This is accomplished by injecting surfactant solution into the contaminated zone. Impacted groundwater characterized by an increase in the concentration of the contaminant is then recovered and treated. 

Several strategies have been described for the preconcentration of sample components present at low concentrations. These techniques include zone sharpening,28-29 on-line packed columns,30 and transient capillary isotachophoresis (cITP).31-32 Other standard laboratory techniques are often used, including solid-phase extraction, protein precipitation, ultrafiltration, etc. Two important points to keep in mind when selecting a concentration protocol are the sample requirements of the method and the potential selectivity on relative concentrations of sample components. The latter point applies to purity and concentration analysis. 

Jimidar, M., Bourguignon, B., and Massart, D. L. (1996). Application of Derringer s desirability function for the selection of optimum separation conditions in capillary zone electrophoresis. J. Chromatogr. A 740(1), 109-117. 

The most important features of liquid membranes are that they olfer highly selective extraction, efficient enrichment of analytes from the matrix in only one step, and the possibility of automated interfacing to different analytical instruments such as liquid chromatography, gas chromatography, capillary zone electrophoresis, UV spectrophotometry, atomic absorption spectrometry, and mass spectrometry [82]. 

Capillary zone electrophoresis is a separation technique that benefits from very high efficiency, not selectivity. This is in contrast to chromatography, for which the converse is true. Differences in mobility in the range of 0.01% can be enough for complete resolution of neighboring peaks. The resolution R is defined as... 

R Vespalec, S Fanali, P Bocek. Consequences of a maximum existing in the dependence of separation selectivity on concentration of cyclodextrin added as chiral selector in capillary zone electrophoresis. Electrophoresis 15 1523-1525, 1994. 

The application of high-performance capillary zone electrophoresis (HP-CZE) in its various selectivity modes has become a very valuable adjunct to HPLC for the analysis of peptides. For synthetic peptides, in particular, both HPLC and HP-CZE now form essential components of the analytical characterization of these molecules. Increasingly, zonal, micellar, or (biospecific) affinity-based HP-CZE procedures with open tubular capillary systems are adapted to allow resolution with extremely high separation efficiencies (e.g., >105 plates per meter) of synthetic or naturally occurring peptides as part of the determination of their structural, biophysical, or functional properties. Illustrative of these capabilities are the results shown in Figure 19 for the separation of several peptides with different charge and Stokes radius characteristics by HP-CZE. 

Several different analytical and ultra-micropreparative CEC approaches have been described for such peptide separations. For example, open tubular (OT-CEC) methods have been used 290-294 with etched fused silicas to increase the surface area with diols or octadecyl chains then bonded to the surface.1 With such OT-CEC systems, the peptide-ligand interactions of, for example, angiotensin I-III increased with increasing hydrophobicity of the bonded phase on the capillary wall. Porous layer open tubular (PLOT) capillaries coated with anionic polymers 295 or poly(aspartic acid) 296 have also been employed 297 to separate basic peptides on the inner wall of fused silica capillaries of 20 pm i.d. When the same eluent conditions were employed, superior performance was observed for these PLOT capillaries compared to the corresponding capillary zone electrophoresis (HP-CZE) separation. Peptide mixtures can be analyzed 298-300 with OT-CEC systems based on octyl-bonded fused silica capillaries that have been coated with (3-aminopropyl)trimethoxysilane (APS), as well as with pressurized CEC (pCEC) packed with particles of similar surface chemistry, to decrease the electrostatic interactions between the solute and the surface, coupled to a mass spectrometer (MS). In the pressurized flow version of electrochromatography, a pLC pump is also employed (Figure 26) to facilitate liquid flow, reduce bubble formation, and to fine-tune the selectivity of the separation of the peptide mixture. 

Triethanolamine can be determined in metalworking and cutting fluids by gas chromatography-mass selective detection of silylated derivatives, by isotachophoresis, by capillary zone electrophoresis with indirect ultraviolet detection, and by spectrophotometry (Kenyon et al, 1993 Fernando, 1995 Schubert et al, 1996 Sollenberg, 1997) and in cosmetics and pharmaceuticals by ion-exclusion chromatography and by reversed-phase high performance liquid chromatography (Fukui et al, 1992 Maurer etal, 1996). 

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