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| - Extension of External Voltage Control ofElectroosmosis to High-pH Buffers
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| - Control of electroosmosis by an applied external voltagefield in capillary electrophoresis has been limited to bufferpH approximately 5 or below. This poor control at higherpH is caused by a high density of surface charge inducedby chemical equilibrium overwhelming the influence ofthe external voltage-induced charges within the electricdouble layer. A tert-butyldiphenylchlorosilane treatmentwas used on fused-silica capillaries to minimize chemically generated ζ-potential where this treatment allowedfor control of electroosmosis over a large pH range (2−10). Blocking the surface with traditional polymer-basedsurface treatments does not work in this application sincethe polymers increase the viscosity within the electricdouble layer and impede electroosmosis. The surfacecreated by this reaction is demonstrated in extremelynarrow capillaries, down to 2-μm internal diameter. Thetreated surface is sterically hindered against acid- andbase-catalyzed degradation reactions typically associatedwith organosilanes. This results in a surface that wasstable to experimental buffer pH extremes, from pH 3 topH 10, and was stable for at least 8 weeks exposed toboth solution and air.
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