Capillary zone electrophoresis

Capillary zone electrophoresis (CZE) provides an alternative to ion interaction chromatography for resolution of metallo cyanide complexes (Costa-Femandez etal. 2000). The procedure may be interfaced with ICP-TOFMS, which permits further resolution of unresolved ionic species. The method is capable of detecting concentrations as low as 50 pg l-1. 

Several modes of CE have been described in the literature over past decade [6, 7], The most common are open tubular or capillary zone electrophoresis (CZE), micellar electrokinetic chromatography (MEKC), microemulsion elec-trokinetic chromatography (MEEKC), capillary electrochromatograpy (CEC), capillary gel electrophoresis, capillary isoelectric focusing and capillary iso-tachophoresis. Three recent reviews by Watzig [113], Tagliaro etal. [114] and Riekkola etal. [115] summarise the current method development options available to manipulate selectivity. In pharmaceutical analysis, CZE, MEKC, MEEKC and CEC are commonly used. 

Method development in CE involves optimising the experimental parameters such as pH, organic modifiers, surfactant additives, ion-pair reagents, cyclo-dextrins, polymer additives, complexation agents and combinations of these additives. The use of pH is a very powerful tool for manipulating and influencing 

Other experimental parameters to be considered include the nature of the column and its dimensions. The recommended columns are fused silica materials with typical IDs of 50-75 pm and column lengths of between 25 and 

Buffers types consisting of phosphates, borates and formates are usually recommended with ionic strengths of 25 and 150mM. Where the CZE system uses a mass spectrometer as the detector, volatile buffers such as ammonium formates, acetates and bicarbonates are used. 

The use of deuterated solvents such as deuterated water has been used to improve the resolution of a number of analytes including pharmaceuticals [116,117], This approach has some very unique benefits such as different ionisation equilibria of polar compounds, higher thermal conductivity and higher density, which can give rise to some dramatic improvements in separation. 

The temperature difference between the center of a column and the wall varies as the square of the radius. Therefore, a small radius reduces the temperature gradient significantly. 

The electro-osmotic flow can be quite beneficial. Because the sample is added at one end, without this flow, only cations or anions could be analyzed during any one run, and neutrals could not be done. With the electro-osmotic flow, the order of elution is anions, neutrals, and cations toward the anode. In addition, the flow speeds up the movement of ions, so the very large or weakly charged ions can be separated with a much shorter column. 

The other factor is the electrophoretic separation of charged particles. The rate of this migration is dependent upon the viscosity of the solution the size and charge of the particles and most importantly, the potential applied. In normal electrophoresis, the potential is a compromise between the need for speed and the need to reduce heat. With capillaries, high potentials can be applied, as much as 300 V/cm to date. 

Therefore, all particles move even the neutral ones are carried along by the electro-osmotic flow. Because most of the charge is at the surface and the diameter is so small, the normal parabolic flow profile of a liquid flowing through a pipe is changed to a flat front, and zones of ions can be formed. 

In addition, the cations and anions are being separated by the normal electrophoretic process. Because of the high potential, this separation can be quite fast. The resolution is excellent, because the small diameter of the tube minimizes concentration broadening, diffusion broadening, and heat broadening. The absence of a gel or particles eliminates eddy migration. 

The wide-ranging applications of chromatography to surfactant analysis have been illustrated. The family of techniques offers so many possibilities for any analysis that the practitioner is often spoilt for choice and must consider carefully what his objectives are—sensitivity of detection, qualitative identification, quantitative determination—and whether there are any time constraints. There is almost certain to be an existing chromatographic analysis which will lead to an acceptable solution. 

This chapter represents the view of the author and is not necessarily the view of Unilever Research. 

ECOSOL Dialkyl-Tetralins in Linear Alkylbenzene, method published by ECOSOL, Brussels, August 1992. 

and Sauer, W. Thin Layer Chromatography—An Introduction, Huthig, Heidelberg, 1991. 

Lafosse, M., Elfakir, C., Morin-Allory, L. and Dreux, M. J. High Resolut. Chromatog., 15(5) (1992), 312-318. 

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Capillary Zone Electrophoresis The simplest form of capillary electrophoresis is capillary zone electrophoresis (CZE). In CZE the capillary tube is filled with a buffer solution and, after loading the sample, the ends of the capillary tube are placed in reservoirs containing additional buffer solution. Under normal conditions, the end of the capillary containing the sample is the anode, and solutes migrate toward... 

Capillary zone electrophoresis also can be accomplished without an electroosmotic flow by coating the capillary s walls with a nonionic reagent. In the absence of electroosmotic flow only cations migrate from the anode to the cathode. Anions elute into the source reservoir while neutral species remain stationary. 

Capillary zone electrophoresis provides effective separations of any charged species, including inorganic anions and cations, organic acids and amines, and large biomolecules such as proteins. For example, CZE has been used to separate a mixture of 36 inorganic and organic ions in less than 3 minutes.Neutral species, of course, cannot be separated. 

The last set of experiments provides examples of the application of capillary electrophoresis. These experiments encompass a variety of different types of samples and include examples of capillary zone electrophoresis and micellar electrokinetic chromatography. 

Conte, E. D. Barry, E. E. Rubinstein, H. Determination of Caffeine in Beverages by Capillary Zone Electrophoresis, ... 

Diet soft drinks contain appreciable quantities of aspartame, benzoic acid, and caffeine. What is the expected order of elution for these compounds in a capillary zone electrophoresis separation using a pH 9.4 buffer solution, given that aspartame has pJC values of 2.964 and 7.37, benzoic acid s pfQ is 4.2, and the pfQ for caffeine is less than 0. 

CE. (sometimes CZE), capillary electrophoresis (or capillary zone electrophoresis)... 

Biomolecule Separations. Advances in chemical separation techniques such as capillary zone electrophoresis (cze) and sedimentation field flow fractionation (sfff) allow for the isolation of nanogram quantities of amino acids and proteins, as weU as the characterization of large biomolecules (63—68) (see Biopolymers, analytical techniques). The two aforementioned techniques, as weU as chromatography and centrifugation, ate all based upon the differential migration of materials. Trends in the area of separations are toward the manipulation of smaller sample volumes, more rapid purification and analysis of materials, higher resolution of complex mixtures, milder conditions, and higher recovery (69). 

DETERMINATION OF POLYPHENOLIC ENANTIOMERS IN GREEN TEA EXTRACT BY CAPILLARY ZONE ELECTROPHORESIS... 

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. 

Electrodriven Separation Techniques encompass a wide range of analytical procedures based on several distinct physical and chemical principles, usually acting together to perform the requh ed separation. Example of electrophoretic-based techniques includes capillary zone electrophoresis (CZE), capillary isotachophoresis (CITP), and capillary gel electrophoresis (CGE) (45-47). Some other electrodriven separation techniques are based not only on electrophoretic principles but rather on chromatographic principles as well. Examples of the latter are micellar... 

Figure 9.5 The generic setup for two-dimensional liquid chromatography-capillary zone electrophoresis as used by Jorgenson s group. The LC separation was performed in hours, while the CZE runs were on a time scale of seconds.

Figure 9.6 Surfer-generated chromatoeletropherogram of fluorescamine-labeled tryptic digest of ovalbumin. Reprinted from Analytical Chemistry, 62, M. M. Bushey and J. W. Jorgenson, Automated instrumentation for comprehensive two-dimensional high-performance liquid chromatography/capillary zone electrophoresis, pp 978-984, copyright 1990, with permission from the American Chemical Society.

ONLINE REVERSE PHASE HIGH PERFORMANCE LIQUID CHROMATOGRAPHY-CAPILLARY ZONE ELECTROPHORESIS - MASS SPECTROMETRY... 

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). 

A. V. Lemmo and J. W. Jorgenson, Two-dimensional protein separation by mictocolumn size-exclusion chromatography-capillary zone electrophoresis , 7. Chromatogr. 633 213-220(1993). 

A. W. Moore, Jr and J. W. Jorgenson, Comprehensive three-dimensional separation of peptides using size exclusion chromatography/reversed phase liquid chromatography/ optically gated capillary zone electrophoresis . Anal. Chem. 67 3456-3463 (1995). 

J. H. Beattie, R. Self and M. P. Richards, The use of solid phase concenti ators for online pre-concentration of metallothionein prior to isofom separation by capillary zone electrophoresis , Electrophoresis 16 322-328 (1995). 

E. J. Cole and R. T. Kennedy, Seleaive preconcenti ation for capillary zone electrophoresis using protein G immunoaffinity capillary chi omatography . Electrophoresis 16 549-556(1995). 

Indirect UV absorbance detection in capillary zone electrophoresis has been used to analyze sodium alcohol sulfates. Excellent reproducibility was obtained when veronal buffer was used as UV-absorbing background electrolyte [302],... 

Butterman, M Tietz, D Orban, L Chrambach, A, Ferguson Plots Based on Absolute Mobilities in Polyarcylamide Gel Electrophoresis Dependence of Linearity of Polymerization Conditions and Application on the Determination of Free Mobility, Electrophoresis 9, 293, 1988. Caglio, S Chiari, M Righetti, PG, Gel Polymerization in Detergents Conversion Efficiency of Methylene Blue vs. Persulfate Catalysis, as Investigated by Capillary Zone Electrophoresis, Electrophoresis 15, 209, 1994. 

Cagho, S Righetti, PG, On the Efficiency of Methylene Blue versus Persulfate Catalysis of Polyacrylamide Gels, as Investigated by Capillary Zone Electrophoresis, Electrophoresis 14, 997, 1993. 

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