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Negative ion field desorption mass spectrometry by clustering with anions
Author(s) -
Zwinselman J. J.,
Fokkens R. H.,
Nibbering N. M. M.,
Ott K. H.,
Röllgen F. W.
Publication year - 1981
Publication title -
biomedical mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.475
H-Index - 121
eISSN - 1096-9888
pISSN - 0306-042X
DOI - 10.1002/bms.1200080706
Subject(s) - chemistry , desorption , salt (chemistry) , ion , inorganic chemistry , potassium , mass spectrometry , tungsten , fast atom bombardment , yield (engineering) , chromatography , organic chemistry , adsorption , materials science , metallurgy
It is shown that under field desorption conditions some less volatile or non‐volatile compounds such as oligosaccharides, sulphonic acids and fatty acids can be ionized below the threshold of field electron emission by clustering with anions. In all cases the sample, together with polyethylene oxide 4000, is dissolved in water. The source of the clustering anion is provided either by a small amount of a salt added to this solution (sugars) or by the compounds themselves (sulphonic and fatty acids). The solution is applied to unactivated and/or slightly activated 10 μm tungsten wire cathodes. Suitable clustering ions for the sugars appear to be [Cl] − , [NO 3 ] − and to a lesser extent [Br] − and [I] − . Most of the sulphonic acids studied give rise to the formation of [M n —H] − ions ( n ⩽5), but their potassium salts yield only unclustered sulphonate anions. However, the addition of a small amount of LiCl to the mixture of benzene sulphonic acid and polyethylene oxide 4000 promotes the formation of clustered anions, [(M—H) 2 Li] − being by far the most abundant if activated cathodes are used. This addition of some LiCl is essential in the case of fatty acids: without LiCl no anions may be desorbed at all from activated wires, but with the presence of LiCl both [M—H] − and the most abundant [(M—H) 2 Li] − anions are easily generated.