Probing reactive sites for ion-molecule reactions of anthraquinones with dimethyl ether using an external source ion trap tandem mass spectrometer and computational chemistry

Gas-phase ion-molecule reactions of anthraquinone derivatives with dimethyl ether (DME) were investigated using an external source ion trap mass spectrometer. Semi-empirical calculations were executed to determine possible reactive sites for the product ions. Collision activated dissociation (CAD) was successfully performed for very low abundance of ion-molecule products. Even for product ions with a relative intensity below 1%, CAD experiments can be successfully performed. Significantly more structural information could be elucidated based on this special feature. Importantly, the CAD spectra of very minor ions could be measured by this ion trap instrument, which significantly enhances the future role of the ion trap as a powerful analytical instrument. CAD of all product ions on anthraquinone compounds typically eliminates neutral molecules such as CO or H2O. A hydration phenomenon in the CAD processes resulting from the precursor ions incorporating one molecule of H2O and then eliminating one molecule of CO was observed in this study. Copyright (C) 2001 John Wiley & Sons, Ltd.