A NEW-TYPE OF PH-STABLE AND DETERGENT-STABLE COATING FOR ELIMINATION OF ELECTROENDOOSMOSIS AND ADSORPTION IN (CAPILLARY) ELECTROPHORESIS

We describe a method to coat fused silica, quartz, or glass electrophoresis tubes with hydrophilic polymers, such as methyl cellulose or dextran, in order to eliminate electroendosmosis and adsorption of solutes onto the tube wall. The coating was not split off upon exposure to a 5% solution of sodium dodecyl sulfate (SDS) at pH around 12 during a period of sixteen days or to 0.5 M HCl (pH 0.3) during 10 days. The high stability of the coating, which is attached to the silica surface via Si-O-Si-C bonds, permits electrophoresis experiments at extreme (besides neutral) pH values and allows short washes of the electrophoresis tubes between the runs with 0.05 M sodium hydroxide (pH 12.7) containing 5% SDS, and with 1 M HCl. These washing solutions release efficiently those solutes which have a tendency to adsorb onto the coating, which is a prerequisite for reproducible runs. The quality of the coating was strongly affected by the surface structure of the commercial fused silica tubing, which may vary from batch to batch. Attempts to standardize the surface structure of any tubing by treatments with NaOH and HCl to obtain a coating, the quality of which is independent of the original surface structure, were not successful. Therefore, it may be necessary to modify certain details of the coating procedure for each new batch of tubing to obtain optimum stability. Alternative coating procedures are therefore described, one of which is of general applicability (see last paragraph in Section 4).