Electroendoosmotic flow

During electrophoresis, cations are transported towards the cathode and they carry molecules of water and other uncharged molecules with them. This phenomenon is called electroendoosmotic flow (EOF) and the magnitude of the flow towards the cathode is given by an equation of Smoluchowski... 

The A term represents the contribution from flow-related dispersion, which occurs from flow inhomogeneity in the packed bed. Under electroendoosmotic flow all velocities are almost equal since the EOF does not depend upon the particle diameter (or more specifically the inter-particle channel diameter), as long as d > 105. Therefore, the only contribution to the A term will be from the change in direction of the flow as it passes through the packed bed. It is expected that the A term will be less in CEC than it is in HPLC, especially with the use of small particles. 

Figure 3 Counter and co-electroendoosmotic flow of negatively charged analytes A, B, and a neutral analyte M in capillary electrophoresis. HEof, electroendoosmotic flow (EOF) observed flow of the individual analyte iigp, flow of analyte without EOF.

While for uncharged analytes the selectivity in CEC and LC is identical, a different selectivity can be expected for charged analytes. Therefore, Tsuda et al. [9,14,17,35,36] introduced an electrochromatographic retention factor for charged analytes. In pressure supported CEC the retention time is dependent upon the electrophoretic mobility uep, the electroendoosmotic velocity ueo, the velocity of the pressurized flow up and the chromatographic retardation. 

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