Dual-opposite Injection Capillary Electrophoresis for the Simultaneous Separation of Anionic and Cationic Compounds

The basic principles, instrumental developments and applications of dual-opposite injection capillary electrophoresis (DOI-CE) technique are reviewed. Two different dual-opposite injection modes are described: electrokinetic injection and sequential hydrodynamic injection. The features of both injection principles are compared, followed by a detailed discussion on the biases of electrokinetic injection and how to reduce them. Flow injection system for automated dual-opposite injection is also briefly discussed. The approaches to the manipulation of the separation selectivity of anionic and cationic compounds in DOI-CE with indirect UV, mixed direct/indirect UV and contactless conductometric detection are highlighted. Finally, the performance of DOI-CE technique is illustrated by a number of practically relevant applications.