In-capillary preconcentration of proteins for capillary electrophoresis using a cellulose acetate-coated porous joint

This work describes the in-capillary preconcentration of proteins using a cellulose acetate-coated porous joint. The capillary wall near the inlet end of a capillary was made porous by HF etching. During the etching process, a voltage was applied across the capillary wall and the electric current across it was monitored. As the current passed through the capillary wall, it became porous. A solution of cellulose acetate in acetone was added to the etched porous joint. After the acetone was evaporated off, a cellulose acetate-coated porous joint was formed. To preconcentrate the protein ions, an electric voltage was applied between the inlet end of the capillary and the coated porous joint; the protein ions electromigrated to the porous joint but could not pass through it, while the buffer ions could pass easily through the joint. After allowing a certain amount of time for protein preconcentration, a separation voltage was applied across the two ends of the capillary, and normal capillary electrophoresis was carried out. The preconcentration factors for cytochrome c, lysozyme, ribonuclease, and chymotrypsinogen were 65, 155, 705, and 800, respectively. The cellulose acetate-coated porous joint was shown to be strong and stable over time, and was used to analyze trace proteins and macromolecules in biological samples.