Electroendosmosis

 Electroendosmosis (EEO) is the flow of solvent in the electric field during electrophoresis. EEO is caused by stationary charged groups in the gel (see Agarose) or along the inner wall of the vessel; negatively charged acidic groups in the gel or silicate groups embedded in glass surfaces bind mobile positively charged counterions electrostatically. The positively charged counterions migrate in the electric field, transporting their water of hydration and thereby giving rise to the water flow of EEO in that direction. Since the flow rate decreases with increasing distance from the glass wall, EEO is responsible for the parabolic profile of the electrophoretic band when a gel is replaced by a polymer solution. EEO can be used to enhance resolution, but more frequently it is suppressed by covering the stationary charged groupings with a neutral polymer.

 EEO can be measured as the displacement in the electric field of uncharged compounds, such as cyanocobalamin in the neutral pH range or mesityl oxide. EEO decreases semilogarithmically with gel concentration, in complete analogy to electrophoretic mobility. Quantitative measurements of electrophoretic mobilities need to be corrected for the EEO.