to be supplied to or removed from the reservoir the other end of the microchannel is connected to a second reservoir 220 a power supply 222 used to generate a separation potential along the length of the microchannel is placed into contact with fluid in the first reservoir using an external electrode in another embodiment a thin film metal electrode integrated into the microfluidic system may be used to form an electrical connection between the power supply and fluid within the microchannel a similar electrical connection 224 is made to the second reservoir to provide a grounding path for the separation potential an additional embodiment is shown in fig3 in this case a substrate 300 is formed from an insulating or high resistivity material for example a rigid or flexible plastic or undoped silicon a conductive layer 302 is deposited over the substrate the conductive electrode layer may be selectively deposited over a specified region of the substrate for example by using a shadow mask during evaporation or sputtering of a metallic thin film or deposited over the entire substrate and removed from regions where it is not desired for example by using photolithography and etching of the unwanted electrode material an insulating layer 304 is deposited on top of the conductive electrode the insulating layer may be formed from a number of materials for example an electrodeposited or vapor deposited polymer.