Characterization of Nonbonded Poly(ethylene oxide) Coating for Capillary Electrophoresis via Continuous Monitoring of...

We examined changes in a poly(ethylene oxide) (PEO) coating by continuously monitoring the electroosmotic flow (EOF) in a fused-silica capillary during electrophoresis. An imaging CCD camera was used to follow the motion of a fluorescent neutral marker zone along the length of the capillary. The PEO coating was shown to reduce the velocity of EOF by more than 1 order of magnitude compared to a bare capillary at pH 7.0. However, it did not reduce EOF efficiently at pH 8.2. The coating protocol was important, especially at an intermediate pH of 7.7. Capillary reconditioning with an acidified solution of PEO was necessary in order to create a stable and efficient coating. In all cases we observed a gradual increase of EOF during extended runs, suggesting that the coating is slowly being degraded. The increase of pH in the cathodic (detection-end) buffer reservoir beyond pH ∼8.0, e.g., as a result of electrolysis, had a large impact on the stability of the coating. This phenomenon may be used for the efficient and fast regeneration of the column surface and provides a simpler and more reliable alternative to pressure flushing of the capillary.