Positive ions collision-induced dissociation

Positive ion collision-induced dissociation (CID) spectra are most frequently used than negative ion CID. However, negative ion mode is more sensitive in... 

Positive ion FAB mass spectra obtained with a double focusing mass spectrometer produced abundant molecular ions ([M] +) of carotenes and xanthophyUs with minimal fragmentation and no detectable thermal decomposition. Fragmentation of the precursor ion was enhanced by collision-induced dissociation (CID) using helium gas. ... 

Fig. 2.57. Identification of a flavonoid diglycoside from unhydrolized chokeberry sample, (a) Positive total ion chromatogram, (b) ion source collision-induced dissociation chromatogram for the ion m/z 303 (quercetin), (c) full scan MS spectrum of the peak at 14.1min, (d) full scan MS-MS spectrum of the [M+H] ion, (e) fragmentation spectrum (MS3) of the m/z 303.3 ion. Reprinted with permission from S. Hakkinen et al. [161].

Figure F4.5.1 Positive ion fast atom bombardment (FAB) with collision-induced dissociation (CID) tandem mass spectrum of pyropheophytin a isolated from spinach leaves. The FAB matrix was 3-nitrobenzyl alcohol.

Fig. 8 Product ion spectra of diverse tropane alkaloids after collision-induced dissociation. Spectra were obtained after positive electrospray ionization and collision-induced dissociation (CID) with nitrogen in a QTrap 4000 instrument. Common structural elements cause generation of corresponding diagnostic fragments, e.g. m/z 124 and 93. For structural assignment of biotransformation products similar fragmentation pattern were produced and interpreted as shown by Chen et al. [6, 7, 51] and He et al. [59]...

Mass spectrometry (MS) and tandem mass spectrometry (MS/MS) play an important role in the identification of unknown compounds. Different ionization techniques have been used in studying isothiazole derivatives, such as electronic ionization (El), desorption chemical ionization (DCI), fast atom bombardment (FAB), field desorption (FD), and chemical ionization (Cl). Different MS/MS experiments have been described, such as investigation of metastable and collision-induced dissociations to study isothiazoles gas-phase ion chemistry. In addition, MS and MS/MS have been used to differentiate isothiazole isomers differing in the position of endocyclic groups or exocyclic substituents <1998THS(2)471, 1999THS(3)369, 2000THS(4)405>. 

Main fragmentations occurring both in the ion source, and in metastable and collision-induced dissociation (CID) experiments involve the losses of a hydrogen atom, HCN, and MeCN. These are competitive processes, whose abundances depend on the position of the nitrogen in the pyridine ring. Stable isotope labeling showed that the loss of HCN occurs from the five-membered ring (Scheme 1). 

Gord JR, Bemish RJ, Freiser BS (1990) Collision-induced dissociation of positive and negative copper-oxide cluster ions generated by direct laser desorption ionization of copper-oxide. Int J Mass Spectrom Ion Processes 102 115... 

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