Capillary electrochromatography open tubular columns

In a study presented by Jinno et al. [124], packed column capillary electrochromatography, open-tubular CEC, and microcolumn liquid chromatography using a cholesteryl silica bonded phase have been studied to compare the retention behavior for benzodiazepines. The results indicated that CEC was a promising method, as it yielded better resolution and faster analysis than microcolumn LC for benzodiazepines. Similar selectivity to HPLC was noted, except for a few solutes that were charged under the separation conditions. Columns packed with the ODS and cholesteryl phases were compared and showed totally different migration orders of the analytes. The retention on the cholesteryl silica sta-... 

Huang, X., Zhang, J., and Horvath, C. (1999). Capillary electrochromatography of proteins and peptides with porous-layer open-tubular columns.. Chromatogr. A 858, 91-101. 

Malik A. Advances in sol-gel based columns for capillary electrochromatography sol-gel open-tubular columns. Electrophoresis 2002 Nov 23(22-23) 3973-3992. 

LC uses mostly packed columns, as the use of open tubular columns in this method is not practical because of the extremely small column diameters required for good separation. In gas chromatography, both packed and open tubular columns can be used, but the latter are far more popular because of their vastly superior properties. The mobile phase is usually forced through the stationary phase at elevated pressure, although other approaches are also possible (e.g., electrically driven flow in electrochromatography (EC), gravity driven flow in classical LC or flow driven by capillary forces in TLC). 

Because of unfavorable mass transfer properties in liquids, highly efficient separations and short separation times potentially available for open tubular columns can be realized only in columns of small internal diameter (< 25 xm) [309]. These columns have very low phase ratios and serious detection problems arise. Several methods have been proposed to Increase the surface area, and hence the stationary phase capacity, by chemical etching of the interior wall [335] or by adhesion of a thin porous silica or polymer layer to the wall [336-338]. The sol-gel process allows an increase in surface area and formation of a retentive chemically bonded phase in a single step. None of these processes, however, adequately address the problems of low retention, low sample capacity, poor sample detectability, and unfavorable handling characteristics that prevent wider use of open tubular columns in capillary electrochromatography. 

Tlie first chiral separation with open-tubular columns in SFC was published by Roder et al. in 1987 [39]. Schurig and co-workers [40] linked permethylated fi-CyD via an octamethylene spacer to polydimethylsiloxane forming a chiral polymer Chirasil-Dex. The polymer was immobilized on the inner surface of fused-silica capillaries and the capillaries were used for so-called unified chromatography including GC, LC, SFC, and capillary electrochromatography (CEC). 

Mayer, S. Schurig, V. Enantiomer separation by electrochromatography in open tubular columns coated with chirasil-dex. J. Liquid Chromatogr. 1993,16, 915. Sezemam, J. Ganzler, K. Use of cyclodextrins and cyclodextrin derivatives in high-performance liquid chromatography and capillary electrophoresis. J. Chromatogr. A, 1994, 668, 509. 

Capillary electrochromatography (CEC) is a miniaturized separation technique that combines aspects of both interactive chromatography and capillary electrophoresis. In this chapter, the theory of CEC and the factors affecting separation such as the stationary phase and mobile phase parameters have been discussed. The chapter focuses on the types and preparation of columns for CEC and describes the progress made in the development of open-tubular, particle-packed, and monolithic columns. The detection techniques in CEC such as the traditional UV detection and improvements made in coupling with more sensitive detectors such as mass spectrometry are also described. The chapter provides a summary of some applications of CEC in the analysis of pharmaceuticals and biotechnology products. 

Capillary Electrochromatography. Capillary electrochromatography (CEC) is a hybrid technique that works on the basic principles of capillary electrophoresis and chromatography [41], This mode of chromatography is used on either packed or tubular capillaries/columns. The packed column approach was introduced by Pretorius et al. [60] in 1974, while open tubular CEC was presented by Tsuda et al. [61] a decade later. In 1984 Terabe et al. [62] introduced another modification in liquid chromatography, micellar electrokinetic capillary... 

Antibiotics represent a chemically quite heterogenous category of compounds, for which the Cl 8 phases appear sorbents of the first choice. A group of these compounds (tetracyclines) was successfully separated by open tubular capillary electrochromatography using Cl8 modified capillaries. The results reported to be obtained in this system were better than those obtained with either monolithic columns or open diol columns [123] (Fig. 10.26). 

Figure 8.7, Schematic representation of a capillary electrochromatography column consisting of a packed bed and open tubular segment separated by a bed retaining frit (top) and the generation of electroosmotic flow in a packed bed (bottom).

M.C. Breadmore, A.S. Palmer, M. Curran, M. Macka, N. Avdalovic and PR. Haddad, On-column ion-exchange of inorganic anions in open tubular capillary electrochromatography with elution using transient-isotachophoresis gradients. 3. Implementation and method development. Anal. Chem., 74, 2112-2118, 2002. 

Y. Zhao, R. Zhao, D. Shangguan, G. Liu, A new type of capillary column for open-tubular electrochromatography. Electrophoresis, 2002, 23, 2990-2995. 

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