The miniaturization of mass spectrometers should strengthen their usefulness in many applications as long as adequate performance is preserved. However, the use of laser-ionization or conventional filament-ionization sources severely hampered miniaturization of mass spectrometers, whereas triode electron emitters with carbon nanoparticle (CNP) film cathodes opened a new path towards realization of micro mass spectrometer since the fabrication of sufficiently small ion sources became possible using a conventional photolithography process.