Pyridine N‐oxide and pyridine‐d5N‐oxide: an electrospray/tandem mass spectrometric study carried out at high mass resolution

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Abstract
A mass spectrometric study of pyridine N‐oxide and pyridine‐d5N‐oxide was carried out with a hybrid quadrupole/time‐of‐flight (TOF) mass spectrometer coupled with an electrospray (ES) source. In addition to the observation of protonated, sodiated, and proton‐bound dimers of pyridine N‐oxide and pyridine‐d5N‐oxide, mass scans revealed the presence of several doubly‐charged ion species. Doubly‐charged ions of m/z 191 were identified as diprotonated tetramers of pyridine N‐oxide; a structure has been proposed for the diprotonated tetramer and its energy relative to that of protonated pyridine N‐oxide has been obtained from geometry optimizations. The principal ion species observed were subjected to collision‐induced dissociation; accurate mass measurements were made of each fragment ion so as to determine its elemental composition. On the basis of mass spectrometric evidence, it is suggested that dissociation of pyridine N‐oxide may occur during the ES process and the resulting fragments become embedded in doubly‐charged ions. The proton affinity for both pyridine N‐oxide and pyridine‐d5N‐oxide was calculated; the difference between these proton affinities was compared with an experimentally determined difference between the proton affinities of pyridine N‐oxide and pyridine‐d5N‐oxide. Copyright © 2005 John Wiley & Sons, Ltd.
Funding Information
  • Natural Sciences and Engineering Research Council of Canada, the Canada Foundation for Innovation, and the Ontario Innovation Trust