Electrospray ionization (ESI) apparatuses and methods of making the same are disclosed. In one embodiment, an ESI emitter comprises a capillary tube filled with a porous monolithic material, wherein the end of the emitter is tapered and the tip of the tapered end comprises a protrusion of the porous monolithic material. One embodiment of the method for making ESI emitters comprises filling a capillary tube with a porous monolithic material and tapering the end of the capillary tube, thereby exposing a portion of the porous material. The exposed portion of the porous material at the tapered end, rather than the capillary tube itself, forms the tip of the ESI emitter.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
 This invention was made with Government support under Contract DE-AC0576RLO1830 awarded by the U.S. Department of Energy. The Government has certain rights in the invention.