Silanol groups fused silica capillary tubes

Fused silica capillary tubes were variously coated for capillary electrophoresis. The chemical process involving a Grignard reaction is shown in equation 30. The silanol groups on the silica surface are treated with alkali, dried, convert to chlorosUanes with thionyl chloride and vinylmagnesium bromide replaces the chlorine atoms with vinyl... 

Toward the end of Section 11.5 we saw that one of the many useful features of fused silica capillary tubing was the ability of its surface silanol groups to lose H" " ions and form a chemically bound layer of negatively charged groups in aqueous solutions at pH above... 

The fused-silica surface also provides another mechanism, electro-osmosis, which drives solutes through the tube under the influence of an electric field. The principle of electro-osmotic flow (EOF) is illustrated in Fig. 1. The inner wall of the capillary contains silanol groups on the surface that become ionized as the pH is raised above about 3.0. This creates an electrical double layer in the presence of an applied electric field so that the positively charged species of the buffer which are surrounded by a hydrated layer carry solvent toward the cathode (negatively charged electrode). This results in a net movement of solvent toward the cathode that will carry solutes in the same direction as if the solvent were pumped through the capillary. This electrically driven solvent pumping mechanism results in a flat flow profile in contrast to... 

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