Collisionally activated dissociation spectra

Cadmium thiocyanates, 17 333-336 Cadmium trifluoroacetates, 17 25, 26 CAD spectra, see Collisionally activated dissociation spectra... 

The enhanced loss of CH3 from the 5P isomer is explained in terms of the lower critical energy for this reaction cf. the 5a-isomer) due to the increased steric strain at the A/B ring junction. It has further been shown 38) that steroid epimers show differences in their collisionally activated dissociation spectra. In this study, steroid fragment ions were employed as targets for collision. 

Mass spectrum of m/z 304 after collisionally activated dissociation... 

Figure for Problem 25-19 Left Mass spectrum of collisionally activated dissociation products from mlz 304 positive ion from atmospheric pressure chemical ionization mass spectrum of cocaine. Right Chromatogram obtained by selected reaction monitoring. [From G. Singh. V. Arora,... 

Tandem mass spectrometry has been particularly effective in molecular struclure dctemiinaiiiins. To increase the number and absolute abundance of peaks in the secondary mass spectrum, it is necessary lit add energy to the separated primary ions. Collisionally activated dissociation tCAD) is frequently used. 

In neutralization-reionization mass spectrometric experiments on CH2Si+ formed by electron-impact dissociative ionization of ClCH2SiH3, Srinivas, Stilzle and Schwarz found evidence for the formation of a viable neutral molecule whose fragmentation pattern and collisional activation mass spectrum were in accord with a H2C=Si structure422. These authors suggested that their experiments supported electron-capture by CH2Si+" as a mechanism for the formation of H2C=Si in interstellar space. Various models have predicted that H2C=Si is one of the most abundant forms of silicon in dense interstellar clouds423. 

The basic NR mass spectrum contains information on the fraction of undissociated (survivor) ions and also allows one to identify dissociation products that are formed by purely unimolecular reactions. NRMS thus provides information on the intrinsic properties of isolated transient molecules that are not affected by interactions with solvent, matrix, surfaces, trace impurities, radical quenchers, etc. However, because collisional ionization is accompanied by ion excitation and dissociation, the products of neutral and post-reionization dissociations overlap in the NR mass spectra. Several methods have been developed to distinguish neutral and ion dissociations and to characterize further short lived neutral intermediates in the fast beam. Moreover, collisionally activated dissociation (CAD) spectra have been used to characterize the ions produced by collisional reionization of transient neutral intermediates [51]. This NR-CAD analysis adds another dimension to the characterization of neutral intermediates, because it allows one to uncover isomerizations that do not result in a change of mass and thus are not apparent from NR mass spectra alone. 

Figure 9 FAB/collisionally activated dissociation MS/MS negative-ion spectra of penicillin G. (Upper) Spectrum taken from an in vivo analysis as shown in Fig. 2. (Lower) Spectrum of the pure drug.

Sulfatides (3-sulfogalactosylceramides) were initially detected by mass spectrometry using FAB ionization but spectrum showed a number of fragmentations which complicates considerably the method (Ohashi and Nagai, 1991). More recently structural characterization of sulfatides by collisional-activated dissociation (CAD) was described in quadrupole ion-trap tandem mass spectro-metric methods with electrospray ionization. With the method [M - H]- ions of sulfatides yield abundant structurally informative ions that permit unequivocal assignments of the long-chain base and fatty acid constituent including the location of double bond (Hsu and Turk, 2004). The major sulfatide molecular species are quantified similarly in the 2 clinical forms (motor and... 

Several desorphon and spray ionization methods can be used to convert S5mthehc polymers into intact molecular or quasimolecular ions (vide supra), whose exact m/z ratio identifies the composition of the polymer. For structural informahon about the polymer, the dissociation behavior or ion-molecule reactions of the polymer ions must be studied. Such reactions, which rarely take place during the soft ionization processes necessary to generate intact gas phase ions from synthetic macromolecules, are most conveniently assessed by tandem mass spectrometry (MS/MS). With MS/MS, a specific precursor ion is mass-selected, so that its reactivity can be investigated without perturbation from the other ions formed upon ionization. The reaction products of this ion are then mass-analyzed and collected in the MS/MS spectrum. MS/MS studies on polymer ions have so far focused on their spontaneous ("metastable") or collision-induced fragmentation. The fragments arising in these reactions are displayed in metastable ion (MI) or collisionally activated dissociation (CAD) spectra, respectively. Customarily, MI spectra acquired with a TOF mass analyzer have been named "postsource decay (PSD)" spectra similarly, CAD is often referred to as CID (collision-induced dissociation). ... 

Because FAB ionization generates a stable protonated molecular ion from underivatized high-mass peptides, it became opportune to investigate the structural information achievable by collisionally-activated dissociation (CAD) of these ions, employing an appropriate tandem mass spectrometer. Early results (43) indicate that some sequence information is obtainable which was not extractable from the normal FAB spectrum. Ions of mass greater than 2000 daltons were selected for collisional activation and potentially the technique can elucidate detailed fragmentation patterns of peptides and their mixtures. Future developments depend on improvements in sensitivity and resolution. 

Figure 3 Third dimension in pyrolysis mass spectrometry approaches (A) linear programmed thermal degradation mass spectrometry [LPTDMS - third dimension = temperature] (B) collisionally activated dissociation of parent ions coupled with scanning of product ions using tandem mass spectrometry [MS/ MS - third dimension = spectrum of product ions] (C) laser microprobe mass analyser [LAMMA - third dimension = spatial resolution].

FAB of amine oxides gives positive ions corresponding to the protonated molecular ion and the dimer ion (85). No negative ion spectrum is seen. Tandem mass spectrometry with collisionally activated dissociation gives structural information (28). 

Fig. 4. Dissociation of the N-acetyllencyl ion P (m/z 156). A DADI/MIKE spectrum (uni-molecular process), B link scan B/E - const, (unimolecular process), C DADI/ MIKE spectrum (collisional activation), D linked scan B/E = const, (collisional activation)...

Figure 1.17. Mass spectrum of ubiquitin Z= 6 charge state under the same conditions as in Figure 1.16 but at high collisional activation (CAD). All the peaks that contained Na + I" pairs have disappeared and are replaced by uncharged Na adducts. This process is consistent with loss of HI where the I" ions paired to an ionized basic residue dissociated as HI. (From Verkerk and Kebarle, with permission from Elsevier.)...

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