On-Line Concentration of Proteins and Peptides in Capillary Zone Electrophoresis with an Etched Porous Joint

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Abstract
A novel approach for on-line concentration of proteins and peptides in capillary electrophoresis (CE) is presented. A short section (∼0.5−1 cm) along the capillary was etched with HF. The etched section became a porous membrane that allowed electrical conductivity but prevented passage of the analyte ions. The capillary was isolated into two parts by the etched section. Thus, we were able to use three buffer vials to perform CE experiments in the capillary by applying high voltages independently. Concentration and separation were performed at the two respective regions. When high voltage was applied to the concentration capillary (between the inlet end and the etched section), proteins and peptides were concentrated at the etched portion, because the porous capillary wall allowed only small buffer ions to pass through and there was no electric field gradient beyond that point. After focusing, the narrow sample zone was introduced into the separation capillary (between the etched section and the outlet end) by hydrodynamic flow or by electroosmotic flow. Finally, conventional CE was carried out for separation of the analytes. Several different concentration schemes for proteins and peptides were successfully demonstrated by using this new approach.