title: Bipolar electrode focusing: simultaneous concentration enrichment and separation in a microfluidic channel containing a bipolar electrode.
abstract: A method for simultaneously concentrating and separating analytes in a buffer-filled microfluidic channel is reported. The approach is based on modulation of the local electric field within the channel and the corresponding opposition of electrophoretic and electroosmotic flow (EOF) velocities. Dye molecules having different electrophoretic mobilities are focused at different locations within the channel where concentration takes place. At least three species, all small dye molecules, can be simultaneously concentrated and separated, with localized enrichment factors up to approximately 600 achieved within 400 s. The enrichment zones affect the electric field profile, as evidenced by significant differences in focusing of single versus multiple analytes. The EOF could be modulated by modifying the channel walls with an appropriate polymer, and this had the effect of increasing both the enrichment factors and resolution of the separation. Numerical simulations provide insights into the underlying fundamental principles for the experimental findings.
authors.affiliation: Department of Chemistry and Biochemistry and Center for Electrochemistry, The University of Texas at Austin, 1 University Station, A5300, Austin, Texas 78712-0165, USA.
authors.forename: Derek R
authors.initials: DR
authors.lastname: Laws
authors.forename: Dzmitry
authors.initials: D
authors.lastname: Hlushkou
authors.forename: Robbyn K
authors.initials: RK
authors.lastname: Perdue
authors.forename: Ulrich
authors.initials: U
authors.lastname: Tallarek
authors.forename: Richard M
authors.initials: RM
authors.lastname: Crooks