Capillary electrochromatography - A high-efficiency micro-separation technique

Capillary electrochromatography (CEC) is a novel separation technique in which mobile phase transport through a capillary (50-200 mu m I.D.) packed with stationary phase particles is achieved by electroosmotic flow (EOF) instead of a pressure gradient as in HPLC. Electroosmotic flow allows the usage of smaller particles and longer columns than in HPLC because of the absence of backpressure. Separation is achieved by partitioning between mobile and stationary phase and-in the case of charged analytes-by differential electrophoretic mobilities. In the reversed-phase mode, capillary electrochromatography has the potential to yield efficiencies five to ten times higher than standard RP-HPLC. For this reason CEC has started to create high interest among chromatographers. This paper will discuss the theoretical background of CEC, demonstrate the feasibility of CEC as a high-efficiency reversed-phase separation technique, compare theoretically achievable results to those obtained in practice and present fundamental studies on operational parameters such as dependence of EOF and efficiency on pH and organic modifier content.