Editing Electron ionization (section)

== Instrumentation ==
[[File:Schematic Diagram of Electron Ionization Instrumentation.jpg|300px|thumb|Scheme of electron ionization instrumentation]]

A schematic diagram of instrumentation which can be used for electron ionization is shown to the right. The ion source block is made out of metal. As the electron source, the [[cathode]], which can be a thin filament of [[tungsten]] or [[rhenium]] wire, is inserted through a slit to the source block. Then it is heated up to an [[Incandescence|incandescent]] temperature to emit electrons. A potential of 70 V is applied between the cathode and source block to accelerate them to 70 eV [[kinetic energy]] to produce positive ions. The potential of the anode (electron trap) is slightly positive and it is placed on the outside of the ionization chamber, directly opposite to the cathode. The unused electrons are collected by this electron trap. The sample is introduced through the sample hole. To increase the ionization process, a weak magnetic field is applied parallel to the direction of the electrons' travel. Because of this, electrons travel in a narrow helical path, which increases their path length. The positive ions that are generated are accelerated by the repeller electrode into the accelerating region through the slit in the source block. By applying a potential to the ion source and maintaining the exit slit at ground potential, ions enter the mass analyzer with a fixed kinetic energy. To avoid the condensation of the sample, the source block is heated to approximately 300&nbsp;°C.<ref name=":0"/>