Gas removal in free-flow electrophoresis using an integrated nanoporous membrane

The performance of continuous microfluidic free-flow electrophoresis (μFFE) is often compromised by the formation of gaseous products caused by electrolysis of water. We show that this adverse effect can be overcome by employing a nanoporous polytetrafluoroethylene (PTFE) membrane attached to a μFFE system which results in efficient removal of any gases formed. The respective assembly was manufactured via laser cutting and lamination. The complete microfluidic FFE chips consist of five layers, viz. (a) two supporting layers, one made of an adhesive transfer foil and the other from poly(ethylene terephthalate), (b) a hydrophobic membrane, (c) a microfluidic structure in a layer of PTFE, and (d) a bottom glass slide. Such a platform warrants a stable flow of electric current over hours of operation at electric field strength of around 500 V∙cm‾ 1 . This is in contrast to conventional FFE microchips where the current decreases to zero within a few minutes (using the same separation parameters). Micropreparative separation of a mixture of three fluorophores was successfully accomplished continuously over 3 h using this micro-FFE chip and was not accompanied by any disturbances caused by formation of gases. Graphical Abstract Microfluidic free-flow electrophoresis chips with an integrated nanoporous PTFE membrane for continuous removal of gaseous hydrolysis products are presented. Their functionality is demonstrated by a stable micropreparative free-flow electrophoretic separation of three molecules over 180 minutes.