Capillary electrochromatography (CEC) combines the best features of capillary electrophoresis (CE) and high performance liquid chromatography (HPLC): high separation efficiency of CE and the versatile selectivity and large sample capacity of HPLC.However, in practice, when CEC was used without pressure, often on a commercial CE instrument, there were problems and difficulties associated with bubbles formation and column dry-out.These problems can be solved by a pressurized CEC (pCEC) system, in which a mobile phase is driven by both a pressurized flow and an electroosmotic flow (EOF).