Electrophoretic focusing preconcentration technique using a continuous buffer system for capillary electrophoresis

Detection and analysis of dilute small volume samples can be achieved by preconcentration techniques. Published techniques use specialized discontinuous buffer systems (sample stacking, field-amplification, and isotachophoresis) or incorporation of a chromatographic preconcentration chamber-capillary. By carefully exploiting flow and electric fields, preconcentration of analytes can be achieved without the need for discontinuous buffer systems or physical chromatographic devices. This focusing is achieved by independently controlling pressure flow and electrophoretic migration of analytes. Initiation of a voltage field at the immediate entrance of the capillary combined with adjusting bulk flow equal and opposite to the electrophoretic migration of the analytes results in preconcentration. Data are presented indicating an increase in local concentration of 200 nm carboxylate modified latex spheres within the immediate volume of the capillary entrance (specifically ∼ 15 pL) using laser-induced fluorescence detection.