Improvement of Porous Electro-conductive Membrane Preparation and Its Application in Sample Injection Pre-concentration in the Capillary Electrophoresis of Proteins

The success rate of porous conductive joint preparation on fused silica capillary was greatly improved by voltage bias control and electroosmosis effect. The column was filled with basic media and a dc voltage was applied between the capillary inlet and the etching reservoir during the etching. The etching was automatically stopped owing to electroosmosis effect when electro-conductivity of the joint occurred, and over etching was thus avoided. The joint was successfully used in on-line electro injection pre-concentration and capillary electrophoresis separation of a model protein mixture of lysozyme and bovine serum albumin in 0.05 M pH 2.50 Tris-H3PO4 with 2%-4% dextran, and a concentration factor up to 300 was obtained as estimated by the peak height. The difference of concentration factor for basic and acidic proteins is discussed. The detection limit for the model proteins was decreased to 10−11 M with a routinely used UV photometric detector (214 nm) by electro-injection pre-concentration for 30 min.