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

Detection and analysis of dilute small volume samples can be achieved by pr econcentration techniques. Published techniques use specialized discontinuo us buffer systems (sample stacking, field-amplification and isotachophoresi s) or incorporation of a chromatographic preconcentration chamber-capillary . By carefully exploiting flow and electric fields, preconcentration of ana lytes can be achieved without the need for discontinuous buffer systems or physical chromatographic devices. This focusing is achieved by independentl y controlling pressure flow and electrophoretic migration of analytes. Init iation of a voltage: field at the immediate entrance of the capillary combi ned with adjusting bulk now equal and opposite to the electrophoretic migra tion of the analytes results in preconcentration. Data are presented indica ting an increase in local concentration of 200 nm carboxylate modified late x spheres within the immediate volume of the capillary entrance (specifical ly similar to 15 pL) using laser-induced fluorescence detection. (C) 2000 J ohn Wiley & Sons, Inc.