Extension of external voltage control of electroosmosis to high-pH buffers

Control of electroosmosis by an applied external voltage field in capillary electrophoresis has been limited to buffer pH approximately 5 or below. Th is poor control at higher pH is-caused by a high density of surface charge induced by chemical equilibrium overwhelming the influence of the external voltage-induced charges within the electric double-layer. A tert-butyldiphe nylchlorosilane treatment was used on fused-silica capillaries to minimize chemically! generated zeta-potential where this treatment allowed for contr ol-of electroosmosis over a large pH range (2-10), Blocking the surface wit h traditional polymer-based surface:treatments does not. work in this appli cation since the polymers increase the viscosity within the electric double :layer and impede electroosmosis. The surface created by this reaction is d emonstrated in extremely narrow capillaries, down to 2-mu m internal diamet er. The treated surface is sterically hindered against acid- and base-catal yzed degradation reactions typically associated with-organosilanes. This re sults in a surface that was stable to experimental buffer pH extremes, from pH 3 to pH 10, and was stable for at least 8 weeks exposed to both Solutio n and air.