Recent applications in capillary electrochromatography (original) (raw)
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Capillary electrochromatography: operating characteristics and enantiomeric separations
Journal of Chromatography A, 1996
Some fundamental aspects of capillary electrochromatography (CEC) (electroosmotic flow, capacity factor, plate height) were studied by carrying out the separation of some neutral compounds with capillaries packed with octadecylsilica particles (ODS). No loss of efficiency up to a linear electroosmotic velocity of 1.3 mm/s was observed for retained analytes (capacity factors varying from 0.7 to 2.5). The extra-column dispersions caused by the frit and the unpacked section separating the frit from the detection window were estimated. Chiral separations of the neutral enantiomers of chlorthalidone by packed capillary electrochromatography was successfully achieved using two approaches: (a) use of the chiral agent, hydroxypropyl-fl-cyclodextrin (HPflCD) directly in the mobile phase with an achiral stationary phase (3/~m ODS); (b) use of a chiral stationary phase (5 /xm HPflCD-bonded silica particles) with an achiral mobile phase. As with liquid chromatography, the second method achieves higher selectivity and resolution in a shorter analysis time.
Analytical separations in open-tubular capillary electrochromatography
ELECTROPHORESIS, 2003
This review represents a summary of recent progress in open-tubular capillary electrochromatography (OT-CEC) for chiral and achiral separations. The OT-CEC approach is an alternative to packed-CEC that could eliminate the problems associated with retaining frits and silica particles. In OT-CEC, the stationary phase is immobilized on the inner walls of the capillary. Preparation of the stationary phase is critical for OT-CEC. The preparation methods for capillary columns include (i) adsorption, (ii) covalent bonding and/or cross-linking, (iii) porous layers, (iv) chemical bonding after etching, (v) sol-gel, and (vi) molecular imprinting. Major developments, potential applications, technical difficulties and advantages associated with these wall coatings in OT-CEC are presented. In addition, the coupling of OT-CEC with mass spectrometry (MS) is briefly reviewed. Several applications of this hyphenated technique for analytical separations are also summarized.
Capillary electrochromatography: A review
Journal of Microcolumn Separations, 1997
. Abstract: Capillary electrochromatography CEC is a modern liquid chromatographic technique which has attracted renewed curiosity from the scientific community in recent years, despite having origins in the 1970s. The growing interest in this field is reflected in the increasing number of scientific publications and presentations dealing with the technique; the majority of work reviewed here is from the last five years. This review concerns itself primarily with both the development of capillary electrochromatography, from early experimentation to the present day, and its widespread application. The fundamental theory is dis-Ž cussed, as well as experimental aspects such as mode of operation isocratic or . gradient and detection. Considerable attention is devoted to CEC columns; in particular, the preparation of frits and their associated problems. A large number of applications are summarised in tabular form, which provides an insight into the capabilities and scope of this technique.
Capillary electrochromatography: An alternative to HPLC and CE
Journal of Separation Science, 2002
CEC is a technique that has attracted increased interest in recent years. It combines the advantages of high efficiency of electrophoretic separation methods with the greater selectivity characteristic of HPLC. In this paper we explore the use of CEC as a potential alternative to conventional HPLC, l-HPLC, and CE. Recent developments, both theoretical and experimental, are reviewed. The practical aspects of application of CEC in various modes of separation are also discussed.
Journal of Microcolumn Separations, 1997
The influence of mobile phase composition variation, organic solvent type, and the concentration of buffer salts on the magnitude of the electroosmotic Ž . flow EOF velocity, retention, and selectivity in capillary electrochromatography Ž . CEC has been investigated systematically. The observed change in EOF is explained in terms of change of solvent and stationary phase properties. These findings provide guidelines for the practitioner to select optimal conditions for CEC separations. On the other hand, it is demonstrated that stationary phase properties also have a profound effect on EOF velocity, solute retention, and selectivity of separation. It is demonstrated that the column packed bed of silica-based reversed-phase particles is the main contributor to EOF in CEC. Variation of stationary phases in CEC can be used in a similar way as in HPLC to improve the selectivity of separation of neutral substances. This also applies to the separation of weakly basic substances like triazines. ᮊ 1997 John Wiley & Sons, Inc. J Micro Sep 9: 399᎐408, 1997 ( ) ( )
Semipreparative Capillary Electrochromatography
Analytical Chemistry, 2001
Capillaries with inner diameters of 550 µm have successfully been packed with 1.5-µm octadecyl silica particles using frits made of macroporous polymers by the UV photopolymerization of a solution of glycidyl methacrylate and trimethylolpropane trimethacrylate. This type of frit is found superior to one made of low-melting point poly-(styrene-co-divinylbenzene) beads. Bubble formation is not observed to occur within these capillary columns under our experimental conditions. Separations can be achieved with sample injection volumes as high as 1 µL. To demonstrate its semipreparative use, a mixture of 500 nL of taxol (20 mM) and its precursor, baccatin III (30 mM), is separated using such a column with a Tris buffer. Capillary electrochromatography (CEC) is a powerful separation technique that combines high-performance liquid chromatography (HPLC) and capillary electrophoresis (CE). It has attracted much interest in the past few years because it has (1) high separation efficiency, (2) high selectivity, (3) low solvent consumption, and (4) low operational costs. Recently, several research groups have presented many impressive applications of CEC. A broad variety of different species, such as corticosteroids, 1 amino acids, 2-4 proteins and peptides, 5-8 carbohydrates, 9 environmental contaminants, 10,11 natural products, 12,13 and pharmaceuticals, 14-16 have successfully been separated using CEC. Several
Chiral separations by open tubular capillary electrokinetic chromatography
Journal of Chromatography A, 1999
The inner walls of 50 mm fused-silica capillaries are etched by ammonium hydrogendifluoride and then modified by the silanization / hydrosilation method with a chiral selector. Three different types of selectors were evaluated: lactone, b-cyclodextrin and naphthylethylamine. Each of the bonded chiral stationary phases provided at least partial separation for one type of racemic solute. These results confirm that bonded organic moieties on the etched inner wall of a capillary can provided sufficient solute-bonded phase interactions to influence the retention of molecules driven through a capillary by electroosmosis or a combination of electroosmosis and electrophoretic mobility.
Journal of Chromatography A, 2000
In capillary electrochromatography (CEC) the propulsion of the mobile phase is effected by electroosmosis. The velocity of the electroosmotic flow is dependent on surface properties of the stationary phase and on bulk properties of the mobile phase. Therefore, in CEC the optimization of the mobile phase composition must take more factors into account than in pressure-driven LC. In this paper, the impact of the electrolyte concentration in the mobile phase and of the volume fraction of the organic mobile phase constituent on the velocity of the electroosmotic flow and on the chromatographic efficiency is investigated for CEC with capillaries packed with octadecylsilica gel. Bias of the data by an open section of the capillary has been excluded by employing completely packed capillaries and detection in a packed section. Acetonitrile as organic constituent of the mobile phase is compared to other possible organic modifiers (polar organic solvents) concerning influence on velocity of the electroosmotic flow and retention of solutes.