An electroosmotic pump unit includes at least a first pump element, at least a second pump element, and an electrode. Each pump element includes a tube, an electrically grounded fluid inlet, a fluid outlet electrically coupled to the electrode, and a porous monolith immobilized in the tube and having open pores having net surface charges. When the electrode applies a voltage across the monoliths, a fluid supplied to the first pump element flows through the pump elements in a direction from a fluid inlet of the first pump element toward a fluid outlet of the second pump element. A plurality of electroosmotic pump units may be connected in series in a pump assembly. The electroosmotic pump unit, or pump assembly, may be connected to an apparatus such as a HPLC.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
 This invention was supported by Department of Energy under DE-SC0006351, and the National Science Foundation under CHE-1011957. The United States government has certain rights in this invention.