Hydrolytically stable amino-silica glass coating material for manipulation of the electroosmotic flow in capillary electrophoresis

A hydrolytically stable amino-silica glass coating material was fabricated inside fused-silica capillaries, using sol-gel technology. Aminopropyltriethoxysilane was used as the precursor in the glass formation process. The net charge at the surface of the coating material depends on the degree of protonation of the amino groups and the degree of ionization of the silanol groups, thus enabling manipulation of the magnitude and direction of the electroosmotic flow (EOF). At low pH (<6.0), the coating bears a net positive charge, which results in an electroosmotic flow from the cathode toward the anode and minimizes the wall-solute interactions of basic species. At high pH (>6.5), the coating surface bears a net negative charge and the coated capillary behaves like an uncoated one, having an EOF in the cathodic direction. The amino-silica glass coating has also been shown to be extremely stable under both acidic and basic conditions. The reproducibility of the electroosmotic mobility of five different capillaries was found to be 7% R.S.D. The utility of the material is shown with the separation of basic proteins, peptides and basic compounds.