A very thin coating for capillary zone electrophoresis of proteins based on a tri(ethylene glycol)-terminated alkyltrichlorosilane

We describe the use of a tri(ethylene glycol)-terminated alkyltrichlorosilane to create a very thin, protein-resistant "self-assembled monolayer" coating on the inner surface of a fused-silica capillary. The same compound has been demonstrated previously on flat silica substrates to resist adsorption of many proteins. As a covalently bound capillary coating, it displays good resistance to the adsorption of cationic proteins, providing clean separations of a mixture of lysozyme, cytochrome c, ribonuclease A, and myoglobin for more than 200 consecutive runs. Electroosmotic flow (EOF) was measured as a function of pH; the coated capillary retains significant cathodal EOF, with roughly 50% of the EOF of an uncoated capillary at neutral pH, making this coating promising for applications requiring some EOF The EOF was reasonably stable, with a 2.9% relative standard deviation during a 24 h period consisting of 72 consecutive separations of cationic proteins. Efficiencies for cationic protein separations were moderate, in the range of 190000-290000 theoretical plates per meter. The coating procedure was simple, requiring only a standard cleaning procedure followed by a rinse with the silane reagent at room temperature. No buffer additives are required to maintain the stability of the coating, making it flexible for a range of applications, potentially including capillary electrophoresis-mass spectrometry (CE-MS).