Capillary electrochromatography

The capillary electrochromatography (English capillary electrochromatography, CEC) is a biochemical method for the separation of molecules in the stationary phase of a chromatographic separation column by electroosmosis. It is a combination of capillary electrophoresis and high performance liquid chromatography.

Principle

At an alkaline pH, the silanol groups are negatively charged on the surface of the inside of the capillary, and the stationary phase. Because overlap for charge balancing positive charges in what is known as electrochemical double layer. In capillaries an electro-osmotic flow is based on application of an electric field on, with a migration of cations along these layers towards the cathode. The migration of cations via their hydration shells into a liquid stream. Due to the different net charges of the analytes and their different degrees of interactions with the stationary phase there is a separation of the migrating particles. The sample is introduced by capillary action into the capillary. By avoiding a high pressure, such as by HPLC, the capillary is less prone to clogging, since the electroosmotic flow is independent of the diameter and the length of the column. The particle size of the column material is therefore chosen more freely.

Theory

The thickness of the electric double layer with the dielectric constant εr δ, electric field constant ε0, the universal gas constant R, absolute temperature, the molar concentration C and the Faraday constant F specifies the following:

The linear velocity of the liquid flow u depends on the Smoluchowski equation ζ inter alia on the zeta potential, the electric field strength E and the viscosity η of the medium.