ON THE PH HYSTERESIS OF ELECTROOSMOTIC MOBILITY WITH CAPILLARY ZONE ELECTROPHORESIS IN SILICA CAPILLARY

A porous gel model of silica-solution interface was proposed to explain the pH hysteresis effect on the electroosmotic mobility with capillary zone electrophoresis in silica capillaries. It is speculated that, under acidic preconditionings of the capillaries, a porous gel layer is formed at the silica-solution interface, and the magnitudes of zeta potential and electroosmotic mobility are then reduced due to the penetration of electrolyte counterions to the gel layer. On the other hand, under basic preconditionings, a fresh silica surfaces is created by dissolution of silica in alkaline conditions, and this would result in higher values of zeta potential and electroosmotic mobility. The Guoy-Chapman-Stern-Grahame model was employed to simulate the pH-dependence of electroosmotic mobility for the silica capillaries with a gelling surface and with a fresh surface. The predicted data were compared with the experimental results and shown to support the explanation.