A miniaturized non-radioactive electron emitter for atmospheric pressure chemical ionization

In atmospheric pressure chemical ionization as usually used in ion mobility spectrometry radioactive beta minus sources provide free electrons with high kinetic energy to initiate a chemical gas phase ionization of the analytes. In this paper we present a simple to manufacture miniaturized non-radioactive electron source to provide the free electrons at atmospheric pressure. Therefore, we generate free electrons by classical thermo emission from a tungsten filament in vacuum. The emitted free electrons are then accelerated towards an electron transparent 300 nm thin Si₃N₄-membrane through which the electrons are transferred from vacuum to atmospheric pressure. The average kinetic electron energy at atmospheric pressure is 8.6 keV.