Microchip capillary electrophoresis (CE) utilizing a sample injector based on a mechanical valve rather than electrokinetic injection can provide improved sample injections, enhanced capabilities, and can eliminate the need for changing the electric field in the separation channel to induce sample injection. In one instance CE electrodes continuously apply an electric field for CE separation along a separation channel. A sample channel is connected to the separation channel at an intersection and has a sample pressure that is greater than that which is present in the separation channel near the intersection. The sample channel does not have electrodes that apply voltages for electrokinetic injection. A sample injector in the sample channel or at the intersection comprises a mechanical valve to control sample injection from the sample channel to the separation channel.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
 This invention was made with Government support under Grant Number RR018522 from the U.S. National Institute of Health and Contract Number DE-ACO576RL01830 awarded by the U.S. Department of Energy. The Government has certain rights in the invention.