Collision induced dissociations

The subsequent step, unimolecular dissociation, has been explained fully in terms of RRKM and quasiequilibrium theory (QET) theories (see Section 6.7). 

The internal energy ab+ is composed of the internal energy prior to the collision, E/ +, and of the amount of energy Q transferred during the collision  

the collision marks a new start of the time scale for the activated ion. As Q Ej + generally holds valid, the internal energy prior to the collision is of minor relevance - though not generally negligible - for the behavior of the activated ion. As may be expected, the CID spectra of stable molecular ions exhibit marked similarity to the 70 eV El spectra of the respective compounds. [113,114] 

Example Except for the intensities relative to the precursor ion, the B/E linked scan CID spectrum of toluene molecular ion, m/z 92, closely resembles the 70 eV El mass spectrum of toluene (Fig. 2.25 for El cf. Chap. 6.4.3). Here, all fragments are due to CID because the molecular ion was generated by field ionization and did not show any metastable decomposition, i.e., Eab+ = 0 and Eab+ = Q. 

The absolute upper limit for the value of Q is defined by the center-of-mass collision energy. Ecu, [115,116] 

However, most collisions are not head-on , but occur at some angle 0. Increasing mAB makes ifintmax decrease, whereas larger wn is beneficial for energy transfer. In CID-MIKES the center of the peak is shifted to the low mass side, i.e., to the low ion translational energy side, because the uptake Q originates from a loss in Slab- [120-125] The relationship between AElab and Q can be expressed as [122] 

In addition to its compact size, another beneficial feature of the quadrupole ion trap mass spectrometer is its convenience for tandem mass spectromefiy (also known as MS/MS or MS ). There are many instances where a single mass spectrum does not allow complete compound identification. Indeed this is a common problem in PTR-MS, as well as in numerous other mass spectrometry investigations. In particular, a peak at a given m z might derive from one or more of several possible compounds. The inclusion of chromatographic 

When a substantial numb of ions are gathered into a lelativdy small volume the electrostatic interactions between the ions can become con arable to tbe strength of interaction of each ion with applied ext nal electric fields. The ion-ion interactions in such circumstances are refeied to as a space charge effect 

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K has been identified as CFl200I-I from its chemistry the reaction mechanism is insertion [115], Collision-induced dissociation (in a SIFT apparatus, a triple-quadnipole apparatus, a guided-ion beam apparatus, an ICR or a beam-gas collision apparatus) may be used to detemiine ligand-bond energies, isomeric fomis of ions and gas-phase acidities. 

Kaye J A and Kuppermann A 1988 Mass effect in quantum-mechanical collision-induced dissociation in collinear reactive atom diatomic molecule collisions Chem. Phys. 125 279-91... 

Collision-induced dissociation mass spectrum of tire proton-bound dimer of isopropanol [(CH2)2CHOH]2H. The mJz 121 ions were first isolated in the trap, followed by resonant excitation of their trajectories to produce CID. Fragment ions include water loss mJz 103), loss of isopropanol mJz 61) and loss of 42 anui mJz 79). (b) Ion-molecule reactions in an ion trap. In this example the mJz 103 ion was first isolated and then resonantly excited in the trap. Endothennic reaction with water inside the trap produces the proton-bound cluster at mJz 121, while CID produces the fragment with mJz 61. 

Time-of-flight mass spectrometers have been used as detectors in a wider variety of experiments tlian any other mass spectrometer. This is especially true of spectroscopic applications, many of which are discussed in this encyclopedia. Unlike the other instruments described in this chapter, the TOP mass spectrometer is usually used for one purpose, to acquire the mass spectrum of a compound. They caimot generally be used for the kinds of ion-molecule chemistry discussed in this chapter, or structural characterization experiments such as collision-induced dissociation. Plowever, they are easily used as detectors for spectroscopic applications such as multi-photoionization (for the spectroscopy of molecular excited states) [38], zero kinetic energy electron spectroscopy [39] (ZEKE, for the precise measurement of ionization energies) and comcidence measurements (such as photoelectron-photoion coincidence spectroscopy [40] for the measurement of ion fragmentation breakdown diagrams). 

As with the quadmpole ion trap, ions with a particular m/z ratio can be selected and stored in tlie FT-ICR cell by the resonant ejection of all other ions. Once isolated, the ions can be stored for variable periods of time (even hours) and allowed to react with neutral reagents that are introduced into the trapping cell. In this maimer, the products of bi-molecular reactions can be monitored and, if done as a fiinction of trapping time, it is possible to derive rate constants for the reactions [47]. Collision-induced dissociation can also be perfomied in the FT-ICR cell by tlie isolation and subsequent excitation of the cyclotron frequency of the ions. The extra translational kinetic energy of the ion packet results in energetic collisions between the ions and background... 

Lain L, Su C X and Armentrout P B 1992 Collision-induced dissociation ofTi (n = 2-22) with Xe bond energies, geometric structures, and dissociation pathways J. Chem. Rhys. 97 4084... 

Bell R C, Zemski K A, Kerns K P, Deng H T and Castleman A W Jr 1998 Reactivities and collision-induced dissociation of vanadium oxide duster cations J. Phys. Chem. A 102 1733... 

By introducing a collision gas into Q2, collision-induced dissociation (CID) can be used to cause more ions to fragment (Figure 33.4). For example, with a pressure of argon in Q2, normal ions (mj ) collide with gas molecules and dissociate to give mj ions. CID increases the yield of fragments compared with natural formation of metastable ions without induced decomposition. 

CoIIisional activation. An ion/neutral process wherein excitation of a (fast) projectile ion is brought about by the same mechanism as in collision-induced dissociation. (The ion may decompose subsequently). 

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. 

Tandem quadrupole and magnetic-sector mass spectrometers as well as FT-ICR and ion trap instruments have been employed in MS/MS experiments involving precursor/product/neutral relationships. Fragmentation can be the result of a metastable decomposition or collision-induced dissociation (CID). The purpose of this type of instrumentation is to identify, qualitatively or quantitatively, specific compounds contained in complex mixtures. This method provides high sensitivity and high specificity. The instrumentation commonly applied in GC/MS is discussed under the MS/MS Instrumentation heading, which appears earlier in this chapter. 

Collision-activated dissociation (CAD) The same process as collision-induced dissociation (CID). 

Armentrout PB (2003) Threshold Collision-Induced Dissociations for the Determination of Accurate Gas-Phase Binding Energies and Reaction Barriers. 225 227-256 Astruc D, Blais J-C, Cloutet E, Djakovitch L, Rigaut S, Ruiz J, Sartor V, Valerio C (2000) The First Organometallic Dendrimers Design and Redox Functions. 210 229-259 Aug6 J, see Lubineau A (1999) 206 1-39... 

Fragmentation occurs because the repeller voltage increases the kinetic energy of the ions, not only making collision-induced dissociation (CID) more likely but also allowing endothermic ion-molecule and solvent-switching reactions to occur. 

Fragmentor voltage Over 220 V Under 90 V 110-150V Collision-induced dissociation effect Poor ionization efficiency Good ionization efficiency... 

Collision-induced dissociation Fragmentation of an ion by collision with a gas molecule. 

Peptides inside the mass specttometet ate broken down into smaller units by coUisions with neuttal helium atoms (collision-induced dissociation), and the masses of the individual fragments are determined. Since peptide bonds are much more labile than carbon-carbon bonds, the most abundant fragments will differ from one another by units equivalent to one or two amino acids. Since—with the exception of leucine and isoleucine—the molecular mass of each amino acid is unique, the sequence of the peptide can be reconstructed from the masses of its fragments. 

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. ... 

Surface methyls have also been synthesized by the collision-induced dissociation of methane physisorbed on Ni(lll) surfaces.[7, 8] This approach avoids the effects of coadsorbates other than hydrogen, and a number of aspects of Ae reaction and decomposition of CH3 and CH fragments on Ni(lll) have been determined.[9] However, the method is relatively complex and best suited for study of low coverages. 

The use of collision-induced dissociation (CID) and MS/MS techniques in conjunction with the API interfaces has dramatically impacted the fleld of environmental analysis. These techniques are now preferred for the determination of triazine compounds in water, soil, crops, etc., owing to the significant improvements in selectivity obtained via the monitoring of precursor-product ion pairs and increased sensitivity due to the reduction of chemical noise. 

Collision-induced Dissociation/Translationally-driven Reactions 215... 

S.3.4.2. Collision-induced Dissociation/Translationally-driven Reactions Tandem-mass spectrometry can be used to determine the threshold energy for collision-induced dissociation (CID),... 

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