Electrophoresis versus electrochromatography

Abstract

AbstractIn separation techniques, such as Liquid Chromatography and Capillary Zone Electrophoresis, separation is performed on the basis of differences in velocity of the various separands, making use of differences in k′ and/or effective mobility.While in chromatography the flow of the eluent is elementary, in electrophoretic techniques the electroosmotic flow is generally suppressed in order to avoid disturbing of the sample zone boundaries, which migrate with a maximal velocity of 10−3 m s−1. This holds especially for isotachophoretic separations, where separands migrate in consecutive zones with minimal detectable lengths of about 0.1 mm.If electroosmotic flow is applied as a transport mechanism, using capillaries as small as about 50 μm, linear velocities of the liquid flow can reach about 2 × 10−3 m s−1. Especially for ionic species with a low effective mobility, this velocity can be a multiple of the electrophoretic migration velocity in the separation compartment. Therefore, anionic, non‐ionic, and cationic separands can migrate in the same direction.Depending on whether repulsive or attractive forces are operative, the electrophoretic separation power can be counteracted or favored. The separation mechanisms making use of (quasi)stationary phases are studied.Plotting the chromatographic behavior versus the electrophoretic shows transition areas to exist between the “purely” electrophoretic techniques and the “purely” chromatographic techniques.It must be stated that most of the recent publications in CZE, especially those with very narrow bore capillaries, can be allocated to the transition areas, sometimes with a strong chromatographic retention component.