TREATMENTS OF FUSED-SILICA CAPILLARIES AND THEIR INFLUENCE ON THE ELECTROPHORETIC CHARACTERISTICS OF THESE COLUMNS BEFORE AND AFTER COATING

Making coated columns in capillary electrophoresis (CE) is a laborious task involving many preparation steps such as etching, leaching, dehy dration, silylation and coating of the inner wall of fused-silica capi llaries. In this work we demonstrate, by testing more than 250 columns , that it is possible to follow up the influence of the different step s on both the electrophoretic behavior of CE columns and the reproduci bility of their preparation. This study was done by carrying out tripl icate measurements of electroosmotic flow values from columns at four different pH values after each step. The effectiveness of the coatings was also investigated by injecting a test-group of basic proteins. It is demonstrated that etching the columns with sodium hydroxide follow ed by a leaching treatment with hydrochloric acid provides higher repr oducibility than by either leaching or etching alone. Dehydration of t he capillary tubing affects the yield of the subsequent silylation rea ction while the best results seem to be obtained by dehydrating the co lumns overnight at 160 degrees C. The silylation degree achieved is de monstrated to also depend on the time of reaction and the concentratio n of silyl reagent. Moreover, a conclusive demonstration about the eff ect of both silylation and polymerization reactions on the final coati ng performance is given. (C) 1998 Elsevier Science B.V. All rights res erved.