Topics - Electron Impact Ionization
Electron Impact Ionization
Electron impact ionization is used in mass spectroscopy to ionize and fragment the sample molecules before mass analysis. The process is a relatively harsh form of ionization producing a wide range of molecular fragments. The electron impact source consists of a heated filament that produces electrons which are accelerated to another electrode called the ion trap. Sample vapor diffuses into the electron beam and become ionized and fragmented, the size depending on the electron energy which is controlled by the accelerating potential on the ion trap electrode. Low energy electrons produce molecular ions and larger fragments, whereas high energy electrons produce many smaller fragments and possibly no molecular ions. After the ions are produced, they are driven by a potential applied to an ion-repeller electrode, away from the ion source into the accelerating region of the mass spectrometer, where mass analysis takes place.