Capillary electrophoresis (CE) is a family of related separation techniques that use narrow-bore fused-silica capillaries to separate a complex array of large and small molecules. High voltages are used to separate molecules based on differences in charge, size and hydrophobic potential. Injection into the capillary is accomplished by immersing the end of the capillary into a sample vial and applying pressure, vacuum or voltage. Depending on the types of capillary and buffers, capillary electrophoresis can be segmented into several separation techniques.

Capillary zone electrophoresis (CZE), also known as free-solution CE (FSCE), is the simplest form of CE. The separation mechanism is based on differences in the charge-to-mass ratio of the analytes. Fundamental to CZE are homogeneity of the buffer solution and constant field strength throughout the length of the capillary. The separation relies principally on the pH-controlled dissociation of acidic groups on the solute or the protonation of basic functions on the solute.

Micellular electrokinetic chromatography (MECC OR MEKC) is a mode of electrokinetic chromatography in which surfactants are added to the buffer solution at concentrations, which form micelles. The separation principle of MEKC is based on a differential partition between the micelle and the solvent. This principle can be employed with charged or neutral solutes and may involve stationary or mobile micelles. MEKC has great utility in separating mixtures that contain both ionic and neutral solutes.

Capillary gel electrophoresis (CGE) is the adaptation of traditional gel electrophoresis into the capillary using polymers in solution as a molecular sieve. This allows solutes having similar charge-to-mass ratios to be resolved by size.

Capillary isoelectric focusing (CIEF) allows amphoteric molecules, such as proteins, to be separated by electrophoresis in a pH gradient generated between the cathode and anode. A solute will migrate to a point where its net charge is zero. At this isoelectric point (the solute’s pI), migration stops and the sample is focused into a tight zone. In CIEF, once a solute has focused at its pI, the zone is mobilized past the detector by either pressure or chemical means.

Capillary isotachophoresis (ITP) is a focusing technique based on the migration of the sample components between leading and terminating electrolytes. Solutes having mobilities intermediate to those of the leading and terminating electrolytes stack into sharp, focused zones. Although it is used as a mode of separation, transient ITP has been used primarily as a concentration technique prior to CZE separation.