Capillary Electrochromatography (CEC) is a novel electroseparation technique in which mobile phase transport through a capillary (50-200 mm i.d.) packed with stationary phase particles is achieved by electroosmotic flow (EOF) instead of a pressure gradient as in HPLC. For neutral compounds, separation is achieved by partitioning between mobile and stationary phase as in HPLC, for charged compounds, by a combination of partitioning and differential electromigration. In the past 2 years CEC has seen a rapidly increasing interest among separation scientists and practical chromatographers. Efficiency improvements of a factor 3-5 compared with standard HPLC have been demonstrated by a number of researchers. Theory even predicts as much as 300,000 theoretical plates/column for the separation of neutral analytes on small particle stationary phase supports (Dittmann and Rozing, 1995). In its current implementation CEC is in particular useful for small neutral or weakly basic/acidic analytes. Although CEC is very similar to HPLC in terms of separation mechanism one has to keep in mind that unlike in HPLC the flow velocity in CEC is determined by properties of the mobile as well as of the stationary phase.
The authors would like to present the results of their recent work in the field of CEC emphasizing the study of the influence of stationary and mobile phase properties on EOF, retention and selectivity in CEC. Different stationary phases (C18, C8, phenyl, mixed mode, immobilized C18) will be compared and the differences in selectivity and ability to generate EOF discussed. The effect of mobile phase pH, buffer ionic strength, and type of organic modifier on retention, selectivity and EOF has been investigated systematically.
These observations together have led to the formulation of practical guidelines for method development in CEC. These will be demonstrated by the separation of e.g. PAHs, triazines and explosives.