Capillary electrophoresis band broadening

The electroosmotic flow profile is very different from that for a phase moving under forced pressure. Figure 12.40 compares the flow profile for electroosmosis with that for hydrodynamic pressure. The uniform, flat profile for electroosmosis helps to minimize band broadening in capillary electrophoresis, thus improving separation efficiency. 

Detectors Most of the detectors used in HPLC also find use in capillary electrophoresis. Among the more common detectors are those based on the absorption of UV/Vis radiation, fluorescence, conductivity, amperometry, and mass spectrometry. Whenever possible, detection is done on-column before the solutes elute from the capillary tube and additional band broadening occurs. 

In packed columns, all three terms contribute to band broadening. For open tubular columns, the multiple path term, A, is 0, so bandwidth decreases and resolution increases. In capillary electrophoresis (Chapter 26), both A and C go to 0, thereby reducing plate height to submicron values and providing extraordinary separation powers. 

Figure 26-26 Lower trace Sample injected electrokinetically for 2 s without stacking is limited in volume to prevent band broadening. Upper trace With stacking. 15 times more sample could be injected (for 30 s). so the signal is 15 times stronger with no increase in bandwidth. [From V Zhao and C. f. Lurie, pH-Mediated Field Amplification OmCotumn Preconcentration of Anions in Physiological Samples for Capillary Electrophoresis, Anal. Chem. 1999, 71,3985.]...

Paegel, B.M., Hutt, L.D., Simpson, P.C., Mathies, R.A., Turn geometry for minimizing band broadening in microfabricated capillary electrophoresis channels. Anal. Chem. 2000, 72(14), 3030-3037. 

Since a chromatographic mechanism (solute partitioning between two phases moving relative to one another) is involved in micellar capillary electrochromatography, the theory outlined above for band broadening in electrophoresis does not apply. Theoretical aspects of MCE have been developed by Terabe et al. [36] and by Davis [37]. 

In capillary gel electrophoresis, one of the major contributors to band broadening, besides the injection and detection extra-column effects, is the longitudinal diffusion of the solute molecules in the capillary tube [14], The theoretical plate number (N) is characteristic of column efficiency ... 

This technique has proven to be a powerful separation technique for the separation of macromolecules, such as antibodies, for two reasons the near flat plug flow profile and the small diffusion constant of the antibodies. These characteristics eliminate band broadening. With both superior separation power and high detection sensitivity, capillary electrophoresis (CE) can separate free Ab and Ag from bound Ab and Ag rapidly and is suitable for immunoassays. CE can combine immunologic recognition with on-line quantitation, microscale... 

Band Broadening in Capillary Electrophoresis Jetse C. Reijenga... 

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