Abstract: A microfabricated silicon chip with a separation material, such as in situ prepared porous polymer monoliths in its microchannels is disclosed. The polymer monoliths are liquid-permeable and serve as microcolumns for liquid chromatography, which are prepared by in situ radical polymerization of a mixture containing vinyl monomers and solvents (porogen) in the microchannels. A method and system are disclosed to generate one or more electrospray plumes from one or more nozzles that provide an ion intensity as measured by a mass spectrometer that is approximately proportional to the number of electrospray plumes formed for analyses contained within the fluid. A plurality of electrospray devices can be used in the form of an array of miniaturized separate electrospray devices for the purpose of generating multiple electrospray plumes from multiple nozzles for the same fluid for analysis.