has function ion source An ion source is a device that is part of a mass spectrometer that ionizes the material under analysis. The ions are then transported by magnetic or electric fields to the mass analyzer. Techniques for ionization have been key to determining what types of samples can be analyzed by mass spectrometry. Electron ionization and chemical ionization are used for gases and vapors. In chemical ionization sources, the material is ionized by chemical ion-molecule reactions during collisions in the source. Two techniques often used with liquid and solid biological samples include electrospray ionization (due to John Fenn PMID 2675315.) and matrix-assisted laser desorption/ionization (MALDI, due to M. Karas and F. Hillenkamp (Measuring Mass: From Positive Rays to Proteins by Michael A. Grayson (Editor) (ISBN 0-941901-31-9))). ionization function device