A fritless, EOF microchip pump for high pressure pumping of aqueous and organic solvents

A fritless, microchip electroosmotic flow (EOF) pump is microfabricated and demonstrated on a planar soda lime glass substrate to be capable of supplying reasonable flow rates under high back pressures, such as that required for micro-high pressure liquid chromatography (micro-HPLC). The microchip EOF pump is composed of a densely packed microchannel containing 800 nm silica particles and was capable of generating a maximum pressure > 1000 psi ( approximately 7 MPa) and a maximum flow rate of 282 nL/min (aqueous cyclohexylamino alkyl sulfonate (CHES) buffer, 10 mM, pH 9.0, 200 V/cm). Other pumping fluids, such as CHES buffer-acetonitrile mixture (50%, v/v), CHES buffer-methanol mixture (50%, v/v), and pure acetonitrile were also used in a characterization of pump performance that included determinations of the maximum flow rate, maximum pressure, and resulting flow rate against an applied, downstream back pressure. The flow rate under a 200 psi ( approximately 1.4 MPa) back pressure at an applied electric field strength of 250 V/cm ranged from 285 nL/min for aqueous CHES buffer to 44 nL/min for CHES buffer-acetonitrile mixture (50%, v/v), indicating that this EOF pump will meet the future requirements of a micro-HPLC system.