Mass Spectra
DART produces relatively simple mass spectra, dominated by protonated molecules + in positive-ion mode, or deprotonated molecules - in negative-ion mode. Depending on the nature of the molecule, other species may be formed, such as M+. from polynuclear aromatic hydrocarbons. Fragmentation may occasionally be observed for some molecules. Multiple-charge ions and alkali metal cation aducts are never observed, but addition of ammonia or other "dopants" to the DART gas stream can be used to form single-charge adducts such as + or - for compounds that would not readily form molecular ions or protonated molecules. For example, the explosives nitroglycerin and HMX do not form -, but readily form - if chloride is present.
Read more about this topic: DART Ion Source
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