Higher energy collision dissociation

In lipid analyses with LC-MS, mass scanning methods have included MS full-scan acquisition with accurate mass, acquiring precursor and fragment exact mass data simultaneously with MSe scan, precursor ion scan and MRM. The most popular fragmentation method in MS/MS experiments has been collision-induced dissociation, but also higher energy collision dissociation has been utilized. 

FTMS/MS data are acquired at a resolving power of 60,000 ( m/z 400). Both collision-induced dissociation (CID) and higher energy collisional dissociation (HCD) are performed for structural identification of analyte molecules. For the latter, the collision cell placed in elongation to the curved linear ion trap is used see 6). Precursor ion isolation is achieved in the linear ion trap for both kinds of fragmentation techniques. As for the molecular (MS mode) ions, also the fragment (MS/MS mode) ions are analyzed in the Orbitrap detector in these experiments. 

Figure 7.8 Representative product-ion ESI-MS spectra of deprotonated bis(monoacyl-glycero)phosphate (BMP) species (i.e., [M—H]") after low-energy CID. Product-ion ESI-MS analyses of 18 0-20 4 BMP (a) and 18 0-22 6 BMP (b) in the negative-ion mode after CID were performed on a Thermo Fisher Q-Executive mass spectrometer. Collision activation was conducted with higher energy coUisional dissociation (HCD) at 24.0 eV and gas pressure of 1 mTorr.

At low energies the abstraction process dominates and at higher energies the exchange mechanism becomes more important. The cross-sections for the two processes crossing at 10 eV. The END calculations yield absolute cross-sections that show the same trend as the experimentally determined relative cross-sections for the two processes. The theory predicts that a substantial fraction of the abstraction product NHjD, which are excited above the dissociation threshold for an N—H bond actually dissociates to NH2D" + H or NH3 during the almost 50-ps travel from the collision chamber to the detector, and thus affects the measured relative cross-sections of the two processes. 

In the case of vibrational excitation of NH3 at a metal surface a very different dependence has been observed [119]. In this case, the vibrational excitation could be attributed to mechanical excitation of the NH3 umbrella mode in the collision with the surface. Finally, it is worth mentioning that at much higher energies, way into the domain of tens of eV s, mechanical excitation will lead to molecular vibrational excitation and dissociation for all molecules, see e.g. [120]. 

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