chapter  14
66 Pages

Chapter Enantioseparations by Capillary Electrochromatography

Capillary electrochromatography (CEC) [1] is, according to the de nition by IUPAC, “a special case of capillary liquid chromatography (CLC), where the movement of the mobile phase through a capillary that is lled, packed or coated with a stationary phase is achieved by electroosmotic ow (EOF) (which may be assisted by pressure).” In this electric eld driven system, “the retention time is determined by a combination of electrophoretic migration and chromatographic retention [2].” CEC experiments are typically performed in capillary electrophoresis (CE) equipment that allow the application of voltages up to ±30 kV and external pressures up to 12 bar at each end of the

capillary column. If equal pressures are applied at both ends, no pressurized ow is generated, yet bubble formation in the capillary can be successfully prevented. Despite the availability of an external pressure system, sample injections are usually carried out electrokinetically due to backpressure restrictions arising from the packing material in the column. In the normal arrangement on-column UV detection is performed near the outlet end leading to longer separation zones (typically 25 cm), while in the so-called short-end injection the separation is performed by injecting the sample at the outlet end yielding a short migration distance to the detector (commonly ∼ 8.5 cm) and hence faster separation (note, both injection and separation are carried out with reversed polarity in this case).