It can be applied most easily to exchangeable protons and deuterons, where such a transformation occurs in the presence of a suitable deuterium source, without any catalyst. The fragmentation pattern contains clusters of peaks 14 mass units apart (which represent loss of (CH2)nCH3… Ions with sufficient internal energy may fragment in a mass spectrometer, which in some cases may degrade the mass spectrometer performance, but in other cases, such as tandem mass spectrometry, the fragmentation can reveal information about the structure of the ion.   . The fragments then produce a …  Prior to these experiments,   electrospray ionization in-source fragmentation was generally considered an undesired effect  however, electrospray ionization using Enhanced In-Source Fragmentation/Annotation (EISA) has been shown to promote in-source fragmentation that creates fragment ions that are consistent with tandem mass spectrometers. It involves the direct introduction of low-energy electrons to trapped gas-phase ions. However, relative to collision-induced dissociation (CID), ETD is advantageous for the fragmentation of longer peptides or even entire proteins. . The fragments of a molecule cause a unique pattern in the mass spectrum. Mass spectral interpretation is the method employed to identify the chemical formula, characteristic fragment patterns and possible fragment ions from the mass spectra. It is one of the most widely used techniques for activation and dissociation of mass selected precursor ion in MS/MS. Electron capture ionization is the ionization of a gas phase atom or molecule by attachment of an electron to create an ion of the form . Rules for the basic fragmentation processes are given by Stevenson’s Rule. He is an ISI Highly Cited Chemist, with over 1,000 publications and an H-index of 94. Cleavage occurs when the radical and an odd electron from the bonds adjacent to the radical migrate to form a bond between the alpha carbon and either the heteroatom or the unsaturated functional group.  This can take place by a process of homolytic cleavage/ homolysis or heterolytic cleavage/ heterolysis of the bond. The cation has a radical on a heteroatom or an unsaturated functional group. Only charged particles will be accelerated, deflected and detected by the mass spectrometer. It is the science that studies ions and molecules in the gas phase, most often enabled by some form of mass spectrometry. Organic chemists obtain mass spectra of chemical compounds as part of structure elucidation and the analysis is part of many organic chemistry curricula. Its applications include the identification of proteins and their post-translational modifications, the elucidation of protein complexes, their subunits and functional interactions, as well as the global measurement of proteins in proteomics. The fragments of a molecule cause a unique pattern in the mass spectrum.  Other rearrangement reactions include heterocyclic ring fission (HRF), benzofuran forming fission (BFF), quinone methide (QM) fission or Retro Diels-Alder (RDA). This technique is a branch of gaseous ion-molecule chemistry. , Fragmentation can occur in the ion source (in-source fragmentation)   where it has been used with electron ionization  to help identify molecules and, recently (2020), with electrospray ionization it has been shown to provide the same benefit in facilitating molecular identification. , Sigma bond cleavage also occurs on radical cations remote from the site of ionization. Hydrogen–deuterium exchange is a chemical reaction in which a covalently bonded hydrogen atom is replaced by a deuterium atom, or vice versa. In mass spectrometry, fragmentation is the dissociation of energetically unstable molecular ions formed from passing the molecules in the ionization chamber of a mass spectrometer. , Rearrangement reactions are fragmentation reactions that form new bonds producing an intermediate structure before cleavage. Ion sources are used to form ions for mass spectrometers, optical emission spectrometers, particle accelerators, ion implanters and ion engines. Siuzdak has also made contributions to virus analysis, viral structural dynamics, as well as developing mass spectrometry imaging technology using nanostructured surfaces.