Capillary electrophoresis band velocity

Capillary electrophoresis (CE) is a routine analytical technique for fast and efficient separation of charged species. Under the influence of an electric field, the ionic species in a sample that is introduced as a plug (or zone) into an electrolyte at one end of a capillary will be separated into discrete bands when they migrate to the other end of the capillary at different electrophoretic velocities. However, Joule heating is an inevitable phenomenon in CE that limits the performance of electrophoretic separation. 

Isotachophoresis. In isotachophoresis (ITP), or displacement electrophoresis or multizonal electrophoresis, the sample is inserted between two different buffers (electrolytes) without electroosmotic flow. The electrolytes are chosen so that one (the leading electrolyte) has a higher mobility and the other (the trailing electrolyte) has a lower mobility than the sample ions. An electric field is applied and the ions start to migrate towards the anode (anions) or cathode (cations). The ions separate into zones (bands) determined by their mobilities, after which each band migrates at a steady-state velocity and steady-state stacking of bands is achieved. Note that in ITP, unlike ZE, there is no electroosmotic flow and cations and anions cannot be separated simultaneously. Reference 26 provides a recent example of capillary isotachophoresis/zone electrophoresis coupled with nanoflow ESI-MS. 

A last variant we mention is capillary zone electrophoresis (Gordon et al. 1988). It employs an electroosmotically driven flow in a capillary, arising from an electric field applied parallel to the capillary, which is charged when in contact with an aqueous solution (Section 6.5). The flow has a nearly flat velocity profile (Fig. 6.5.1), thereby minimizing broadening due to Taylor dispersion of the electrophoretically separated solute bands. 

---