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field desorption
Field desorption (FD) is a method of ion formation used in mass spectrometry in which a high-potential electric field is applied to an ''emitter'' with a sharp surface, such as a razor blade, or more commonly, a filament from which tiny "whiskers" have formed. This results in a high electric field which can result in ionization of gaseous molecules of the analyte. Mass spectra produced by FD have little or no fragmentation because FD is a soft ionization method. They are dominated by molecular radical cations M+. and less often, protonated molecules . The technique was first reported by Beckey in 1969.〔Beckey H.D. ''Field ionization mass spectrometry.'' Research/Development, ''1969'', 20(11), 26〕
==Mechanism==
In FD, the analyte is applied as a thin film directly to the emitter, or small crystals of solid materials are placed onto the emitter. Slow heating of the emitter then begins, by passing a high current through the emitter, which is maintained at a high potential (e.g. 5 kilovolts). As heating of the emitter continues, low-vapor-pressure materials get desorbed and ionized by alkali metal cation attachment.
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