Pulsed electron source for atmospheric pressure chemical ionization in ion mobility spectrometry

Abstract

Ion mobility spectrometers (IMS) are measurement devices for fast and ultra-sensitive trace gas analysis. Most IMS employ radioactive electron sources, such as 3 H or 63 Ni, to provide free electrons with high kinetic energy at atmospheric pressure for initiating a chemical gas phase ionization of the analytes. The disadvantage of these radioactive materials are legal restrictions and the electron emission cannot be adjusted or turned off. Therefore, we developed a non-radioactive electron source and replaced the 3 H-source of our existing IMS, leading to comparable spectra. An advantage of our non-radioactive electron source is that it can operate in a fast pulsed mode. By optimizing the geometric parameters and developing fast control electronics, we can achieve short electron emission pulses with high intensities and adjustable pulse width down to a few nanoseconds. This allows to control the ionization process, which can enhance the analytical performance of the IMS. Furthermore, a miniaturized non-radioactive electron source is desirable, e.g. for hand-held IMS devices. Therefore, we developed an emission current control for field emitter cathodes and investigated their suitability for this application.