A new electro-osmotic pump based on silica monoliths

A high-pressure electro-osmotic (EO) micro-pump fabricated by a sol–gel process is shown to be potentially effective as a fluid-driving unit on chip-scale analytical systems. A silica monolithic matrix with a morphology of micron-scaled through pores was synthesized within the 100 μm inner diameter (i.d.) fused-silica capillary of the micro-pump. The monolith bonds directly with the capillary wall such that frits with large pressure loss are unnecessary. This pump uses electro-osmotic flow to propel liquid solution with no moving parts. The Nafion® housing design in the cathode chamber prevents flow leakage into the electrode reservoir from the flow channel and hence maximizes the pressure build-up. It also eliminates electrolytic bubble interference from the flow channels and provides ionic channels for current penetration simultaneously. As the monolith is silica-based, this pump can be used for a variety of fluids, especially for organic solvents, such as acetonitrile and methanol, without swelling and shrinking problems. The maximum flow rate and maximum pressure generated by the 100 μm i.d. monolithic pump are 2.9 μL/min and 3 atm for deionized water at 6 kV applied voltage. These results indicate that the pump can provide sufficient pressure and flow for miniaturized HPLC and micro-total-analysis systems (μ-TAS). A simple universal pressure pump curve collapses the data for a variety of working fluids and voltage.