An on-line electrophoretic concentration method for capillary electrophoresis of proteins

A simple on-line electrophoretic concentration method for capillary electrophoresis of proteins with a semipermeable hollow fiber is proposed. A short, semipermeable hollow fiber is connected to the inlet end of a capillary. An injection electric field is applied across the hollow fiber. Protein samples are electromigrated into the hollow fiber from a sample vial. Since the protein ions cannot pass through wall of the hollow fiber, protein ions are concentrated in the hollow fiber. After a certain period of injection (concentration) time, an electric field is applied across the hollow fiber and the capillary, and a conventional CE is carried out. The concentration effect of the method has been demonstrated successfully with model protein samples, cytochrome c, lysozyme, ribonuclease A, and alpha-chymotrypsinogen A. Experimental results show that the concentration factor is increased with the injection (concentration) time and the electrophoretic mobility of the proteins. When the injection (concentration) time is 60 s, CE detection limits of the model proteins can be lowered by 1000-fold for the present method. Factors affecting the concentration factors and the further improvements of the method are discussed.