Differences between collisionally activated and electron-transfer dissociations found for CH2X2(X = Cl, Br, and I) by using alkali-metal targets

摘要

High-energy collisionally activated dissociation (HE-CAD) and high-energy electron-transfer dissociation (HE-ETD) on collisions with alkali-metal targets (Cs, K, and Na) were investigated for CH2X2+ (X = Cl, Br, and I) ions by tandem mass spectrometry (MS/MS). In the HE-CAD spectra observed, peaks associated withCH(2)X(+) ions formed by a loss of a halogen atom are always predominant regardless of precursor ions and target metals. The observation of the predominant CH2X+ ions is explained by the lowest energy levels of the fragments of CH2X++ X among the possible fragment energy levels and internal-energy distribution in HE-CAD. In the charge-inversion spectra, relative peak intensities of the negative ions formed by HE-ETD strongly depend on the precursor ions and the target metals. While the CHCl2- ion was predominant in the spectra of CH2Cl2+ regardless of target species, the most intense peaks in those of CH2Br2+ and CH2I2+ were ascribed to either Br- or CH2Br- and either I- or I-2, respectively, depending on the target metals. The dependence of the relative intensities of the fragment ions by HE-ETD on the precursor ions and target species are discussed on the basis of the energy levels of the neutral fragments and the narrow internal-energy distribution resulting from the near-resonant neutralization. It was demonstrated that HE-ETD using the alkali-metal targets provided rich information on the dissociation of the neutral species.