Electroosmotic flow chromatography

Because micelles are negatively charged, they migrate toward the cathode with a velocity less than the electroosmotic flow velocity. Neutral species partition themselves between the micelles and the buffer solution in much the same manner as they do in HPLC. Because there is a partitioning between two phases, the term chromatography is used. Note that in MEKC both phases are mobile. ... 

Fujimoto, C., Sakurai, M., and Muranaka, Y. (1999). PEEK columns for open-tubular liquid chromatography with electroosmotic flow. /. Microcolumn Sep. 11, 693-700. 

As in the case of normal chromatography both stationary and mobile phases are also required in NLC. On the other hand, in NCE hydrophilic channel walls with improved control over electroosmotic flow are required for better separation of biological samples. Briefly, the separation efficiencies and selec-tivities in NLC and NCE depend on the properties of the microchannels, and, therefore, surface modification of the microchannel is usually necessary to achieve good separation of a variety of analytes. Recently, Muck and Svatos... 

Basically, capillary electrochromatography (CEC) is a hybrid technique of HPLC and CE [1-3], which was developed in 1974 by Pretorius et al. [4]. CEC is expected to combine high peak efficiency, which is a characteristic of electrically driven separations, with high separation selectivity. As is the case for electrophoresis, a voltage is applied across the separation plateform and sample moves via electroosmotic flow (EOF). However, in analogy to liquid chromatography, the separation device contains a solid... 

Figure 4.2 Classification of electrophoresis according to the contribution of the electroosmotic flow. CZE, Capillary zone electrophoresis MECC, micellar electrokinetic capillary chromatography CEC, capillary electrochromatography cIEF capillary isoelectric focusing cGE, capillary gel electrophoresis.

Because the electroosmotic flow affects the amount of time a solute resides in the capillary, both the separation efficiency and resolution are related to the direction and flow of the EOF. The EOF flow profile, as shown in Figure 4.7, is comparatively pluglike. Unlike the laminar flow that is characteristic of pressure-driven fluids,5 the EOF has minimal effect on resistance to mass transfer. As a result, the plate count in a capillary is far larger than that of a chromatography column of comparable length. 

We note that electroosmotic flow, originating at any charged interface (i.e., almost any real interface), is an effective mechanism for relative phase displacement. Its use in chromatography has been championed by Knox and co-workers [38]. 

Janini GM, Muschik GM, Issaq HJ. Micellar electrokinetic chromatography in zero-electroosmotic flow environment. J Chromatogr B Biomed Appl 1996 683 29. 

The use of electroosmotic flow of the mobile phase in HPLC was first suggested in 1974 [6] to replace pressure-driven flow. However, it became a practical proposition only after the introduction of fused silica capillary columns in gas chromatography. The growing need in life sciences and biotechnology... 

A high electroosmotic flow through the stationary-phase particles may be created when the appropriate conditions are provided. This pore flow has important consequences for the chromatographic efficiency that may be obtained in CEC. From plate height theories on (pressure-driven) techniques such as perfusion and membrane chromatography, it is known that perfusive transport may strongly enhance the stationary-phase mass transfer kinetics [30-34], It is emphasised... 

V. P. Andreev and N. V. Shirokih, Electroosmotic flow profile in the capillary made of several sections, 20th Int. Symp. on Capillary Chromatography, Proceedings on CD, 1998, paper H 11. 

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