Two approaches were used to prepare a series of surface-modified capillaries. In the first, a sublayer was formed by coupling y-methacryloxypropyltrimethoxysilane to the surface silanol groups forming an SI-0 bond; a top layer was then formed by polymerizing acrylamide in the capillary, which reacted with the sublayer. In the second approach, a sublayer was formed by silanol chlorination, followed by Grignard coupling of vinylmagnesium bromide to form an Si-C bond at the surface; a top layer was formed by polymerizing either acrylamide (AA), dimethylacrylamide (DMA), N-acryloylaminoethoxyethanol (AAEE), or N-acryloylaminopropanol (AAP) onto the sublayer. The Si-Cpoly( AA) capillaries were more stable and produced an approximately 10-fold lower electroosmotic flow compared to the Si-0-poly(AA) capillaries. The Si-C sublayer was used to compare the performance of all four top layers. Electroosmotic flow decreased in the order: Si-0-poly(AA), Si-C-poly(AA), Si-Cpoly( AAEE), Si- C-poly(DMA), and Si- C-poly(AAP). Si- C-poly(AA) showed evidence of irreversible degradation at pH 9 already after 40-50 runs. Si-CpolyAAP- coated capillaries demonstrated superior efficiency and migration time reproducibility for a number of alkaline proteins and for fluorescently labeled ovalbumin. Excellent performance was maintained, in the case of poly(AAP), for a least 300 runs (of 30 min duration) at pH 9.0.

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