Collisionally activated

For themial unimolecular reactions with bimolecular collisional activation steps and for bimolecular reactions, more specifically one takes the limit of tire time evolution operator for - co and t —> + co to describe isolated binary collision events. The corresponding matrix representation of f)is called the scattering matrix or S-matrix with matrix elements... 

Because there is little fragmentation on FD, it is necessary to activate the molecular or quasi-molecular ions if molecular structural information is needed. This can be done by any of the methods used in tandem MS as, for example, collisional activation (see Chapters 20 through 23 for more information on tandem MS and collisional activation). 

A product ion scan. Source ions (mT, f,, . .., fs ) are selected by setting Ql, in this case, to pass only m,. Collisional activation of these ions in Q2 induces dissociation to give fragment ions (f,, fj, f, ), which are detected by scanning Q3. The symbolism for this process is shown. 

Quadrupole, Q3, is set to pass only the product ions under investigation. All the ions from the ion source are scanned by Ql and passed successively into Q2, where collisional activation occurs. Those ions that fragment to give product ions of interest are revealed by the appearance of the product ions in Q3 (Figure 33.7). 

Collision of normal ions from the first quadrupole with gas molecules in the second quadrupole increases fragmentation, a process known as either collisionally induced dissociation (CID) or collisionally activated decomposition (CAD). 

Collision-induced dissociation (or decomposition), abbreviated CID. An ion/neutral process wherein the (fast) projectile ion is dissociated as a result of interaction with a target neutral species. This is brought about by conversion during the collision of part of the translational energy of the ion to internal energy in the ion. The term collisional-activated dissociation (or decomposition), abbreviated CAD, is also used. 

B. a term meaning the strength of a magnetic field, often used to refer to a magnetic field or sector B/E. a method of linked scanning for metastable ions, which uses combined m netic and electric fields B /E. a method of linked scanning for metastable ions, which uses combined magnetic and electric fields CAD. collisionally activated decomposition... 

Thiiranium salts, l-methyI-2-methylene-1-oxide, 7, 134 Thiiranium salts, I-phenyl-collisional activation spectra, 7, 135 Thiiranium tetrafluoroborate, 2,3-di-t-butyl-l-methyl-inversion barriers, 7, 134 Thiiranium ylides formation, 7, 174, 175 Thiiran-2-ones... 

The principle of MS/MS for direct analysis of a multicomponent system is shown in Figure 6.18, in which the first mass spectrometer (MS I) operates with soft ionisation (FI, FD, Cl, LD), and thus produces an ensemble of molecular ions (M + H+, M — H+, or adducts). For identification of molecule ABC only ABC+ is allowed to enter an interface or fragmentation zone for excitation by collisional activation, laser radiation or surface-induced dissociation. Within the time of one vibration (10-13s), ABC+ dissociates into fragments characterising the original molecule. They are separated and detected by MS II [226]. Soft ionisation with FI/FD produces low ion yields, which may be insufficient for MS/MS LVEI (typically at 20 V) can be an alternative. Complete analysis of a multicomponent system is carried out in some 20 min. 

An insight into the equilibria present in solutions of several complexes of the type (R3P)2HgX2 (X = C104, CF3COO) is provided by electrospray mass spectrometry (ES MS) (cf. Section 6.9.2.1.8). 39 In all cases the principal ions [(R3P)2HgX]+ are observed, even if these ions and other ionic constituents of the equilibria are known to be labile on the NMR timescale. In the presence of excess R3P the principal ions [(R3P)3HgX]+ appear. Also fragments of collisionally activated decomposition (CAD, can be influenced and controlled to some extent) are detected, e.g., [(R3P)HgX]+. 

Voyskner, R. D. Pack, T. Investigation of collisional-activation decomposition process and spectra in the transport oregion of an electrospray single-quadrupole mass-spectrometer. Rapid Comm. Mass Spectrom. 1991, 5, 263-268. 

Both collisional activation (in ion traps) and post source decay (in curved field reflectron TOF analyzers) have been used successfully to obtain sequence ions from peptides prepared in situ on the sample holder. Single Dalton mass windows are advantageous for precursor selection, as are realized in ion-trap and trap-TOF configurations. Publicly available search algorithms can be used... 

Cargile, B. J. McLuckey, S. A. Stephenson, J. L. Identification of bacteriophage MS2 coat protein from E. coli lysates via ion trap collisional activation of intact protein ions. Anal. Chem. 2001, 73,1277-1285. 

In order to avoid such uncontrolled collisional activation, we chose to use apparatus which is closely related to the ion-source reaction chambers developed for thermal ion-molecule equilibria (see preceding Section A). In fact, sources like those shown in Figures 4 and 7 are well suited for providing thermalized ions however they provide somewhat low ion intensities, typically some 50,000 counts/s of a given major ion in a mass spectrum after mass analysis. However, such intensities are completely sufficient for CID threshold measurements and the source... 

The charge reduction reactions occurred prior to any collisional activation in the second quadrupole Q2, which indicates that the activation energy for this reaction is very low. These results show that in the presence of a multiple charge even N-H hydrogens can become sufficiently acidic and engage in protonation of water molecules. 

Apart from the widely studied silver(i) A-heterocyclic carbenes, Stoltz and Beauchamp made the first report on the gas-phase synthesis of silver(i) Fischer carbenes from the loss of N2 in various diazo malonates upon electrospray ionization and subsequent collisional activation.118 The carbenes generated were capable of undergoing multiple Wolff rearrangements and loss of CO (Scheme 18). 

The major fragmentation in mass spectra of 1,2,5-oxadiazoles is attributed to the loss of nitrile and nitrile oxide or expulsion of NO. The conversion of 3,4-dicyano-l,2,5-oxadiazole-2-oxide (3,4-dicyanofuroxan) 10 to cyanogen iV-oxide 11 (Equation 5) was investigated under the conditions of collisional activation (CA) and neutralization-reionization (NR) mass spectrometry. Flash vacuum thermolysis mass-spectrometry (FVT-MS) and flash vacuum thermolysis infra-red (FVT-IR) investigations of furoxans 10, 12, and 13 reveal that small amounts of cyano isocyanate accompany the formation of the main thermolysis product 11 <2000J(P2)473>. 

Online coupling of flash-vacuum pyrolysis and mass spectrometry was applied to 3,4-dicyano-l,2,5-oxadiazole-2-oxide (dicyanofuroxan). The 1,2,5-oxadiazole is almost quantitatively pyrolyzed at 500-600 °C. Using collisional activation, the main pyrolysis products were identified as NCCNO and (CN)2 <1997BSB545>. 

Most nitrile oxides are unstable, some of them are explosive. This fact hinders the study of their physical properties. Nevertheless, there are a number of publications concerning not only stable but also unstable nitrile oxides. In particular, mass spectral data for nitrile oxides among other unstable compounds containing an N+-X bond are summarized in a review (9). In such studies, the molecular ions must be generated using indirect procedures, including dissociative electron ionization, online flash-vacuum pyrolysis mass spectrometry, or ion-molecular reactions. Their characterization is mainly based on collisional activation and ion-molecular reactions. 

The first mass analyzer was used to select a given m/z value and those ions would be transmitted to the collision region where they would undergo collisional activation. Subsequent decomposition of the excited ions resulted in characteristic fragment ions (with equally characteristic... 

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