delta-Gluconolactone was covalently coupled with aminopropyl-derivatized capillary, creating hydrophilic brushes on the inner wall of the capillary. The hydrophilic coating provided suppression of EOF and minimized protein adsorption, resulting in the separation of basic proteins and DNA with efficiencies up to 450 000 plates/m. The intra- and inter-day repeatabilities of the coating referring to the migration times of the four tested proteins were satisfactory with RSD of no more than 1.1 and 1.8% (n = 5), respectively. Two hundred consecutive runs were performed with negligible change in migration times and efficiency.