Fast Atom Bombardment Mass Spectrometry: an Useful Technique for Structural Characterization of Pyrylium, Thiopyrylium and Pyridinium Cations

It is shown that fast atom bombardment (f.a.b.) mass spectrometry is well suited for the study of the title compounds (thirty nine examples are given). Glycerol and bis- (2-hydroxyethyl) sulphide appear to be the best matrices. Spectra are characterized by large peaks corresponding to the intact cations. The degree of fragmentation is generally low, but significant peaks, related to the substituents on the heteroaromatic nucleus, are observed. Alkyl substituents are responsible for alkane, alkene, or alkyl losses. Unusual fragmentation patterns, observed in the spectra of halogeno- and nitro-derivatives, are discussed in terms of bombardment-promoted solution reactions. A simple approach for accurate (3-7 p.p.m.) mass measurements, using a peak matching unit and KCI- or NaCI-glycerol solutions as the reference substance, is also presented.