Resonant electron capture mass spectrometry of free fatty acids: examination of ion structures using deuterium-labeled fatty acids and collisional activation.
The structures of [M-H](-) ions generated from free fatty acids in resonant electron capture at energies of 1.2 and 7.2 eV were investigated using deuterium-labeled isotopomers and collision-induced dissociation. The [M-H](- small middle dot) ions occur in both a carboxylate anion and a carbanion form. While the formation of the carboxylate anion at 1.2 eV involves the loss of a carboxylic hydrogen, that at 7.2 eV involves the loss of a hydrogen from different positions in the aliphatic chain followed by a rearrangement of a carboxylic hydrogen on to the radical site in the chain. The [M-H-H(2)O](-) ion which is a minor ion in the resonant electron capture spectrum at 7.2 eV is shown to be a precursor for the charge-remote fragment ions corresponding to formal losses of a hydrogen and elements of alkanes. The [M-H-H(2)O](-) ion corresponding to the second major ion in the resonant electron capture spectrum at 7.2 eV is demonstrated to be consistent with a cyclopentanone anion structure. On the basis of new insights obtained in the present study and taking into account previous results, an updated proposal is presented for the mechanism of charge-remote fragmentation which operates in resonant electron capture of free fatty acids at 7.2 eV.
Voinov
Valery G
VG
University of Antwerp (UIA), Department of Pharmaceutical Sciences, Universiteitsplein 1, B-2610 Antwerp, Belgium.
Van den Heuvel
Hilde
H
Claeys
Magda
M
D003903:Deuterium; D005230:Fatty Acids, Nonesterified / Q000032:analysis*; D007553:Isotope Labeling; D013058:Mass Spectrometry; D016339:Spectrometry, Mass, Fast Atom Bombardment
D005230:Fatty Acids, Nonesterified; D003903:Deuterium