Collision-induced dissociation -produced mass

The premise is to utilise a liquid film to provide a reaction environment which can be dynamically controlled in terms of heat and mass flux (influx/effiux) and to complement this with the on-line monitoring technique of Atmospheric Pressure chemical Ionisation (APcI)-Ion Trap Mass Spectrometry (ITMS). This technique allows the flux of protonated molecular ions (Mlf to be directly monitored (mass spectral dimension 1) and to fragment these species under tailored conditions within the ion trap (Collision Induced Dissociation (CID),mass spectral dimension 2), to produce fragment ions representative of the parent ion. This capability is central to allowing species with a common molecular weight to be quantified, for example butan-2,3-dione (MW=86 MH =87, glucose degradation product) and 3-methylbutanal (MW=86 MH =87, Strecker aldehyde from leucine). 

Dua et al. employed collision-induced dissociation (CID) mass spectra to produce molecular precursors that were selected to yield OSCN , ONCS , and OCNS (23). When combined with the aforementioned theoretical calculations, the CID spectra provided evidence that OSCN is a product of the oxidation of SCN by H2O2, but it was suggested that some of the other ions that were observed by Arlandson et al. were possibly due to ONCS (or other isomers). In addition to conflicting conclusions that arise when comparing the aforementioned theoretical and spectroscopic studies, it is noted that many of the experimental results that have been previously reported appear to be inconsistent with the estimated lifetimes of h5rpothiocyanite under the conditions of the experiments (vide infra). 

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. 

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. ... 

FAB and LSIMS are matrix-mediated desorption techniques that use energetic particle bombardment to simultaneously ionize samples like carotenoids and transfer them to the gas phase for mass spectrometric analysis. Molecular ions and/or protonated molecules are usually abundant and fragmentation is minimal. Tandem mass spectrometry with collision-induced dissociation (CID) may be used to produce abundant structurally significant fragment ions from molecular ion precursors (formed using FAB or any suitable ionization technique) for additional characterization and identification of chlorophylls and their derivatives. Continuous-flow FAB/LSIMS may be interfaced to an HPLC system for high-throughput flow-injection analysis or on-line LC/MS. 

Multiresidue determination of QUIN antibiotics using liquid chromatography coupled to ACPI-MS and MS/MS was also described (197). In the source, collision-induced dissociation was used to optimize fragmentation to produce mass spectra consisting of the protonated molecule and two characteristic fragment ions of nearly equal intensity. Selected ion monitoring of three ions per QUIN yielded a sensitive detection in catfish muscle extracts (detection limits of 0.8-1.7 yug/kg). An MS/MS was used to increase the specificity and selectivity of analysis. The preseparation step was very simple only the LLE procedure is required. 

Fig. 17.8. MS/MS schematic representation of MS/MS by quadrapole mass spectrometers. (A) Sample entry normally via ESI. (B) Precursor ion selection allowing only the ion of interest to continue through the mass spectrometer. (C) Collision-induced dissociation of the ion within a gas cell normally containing argon to produce fragments. (D) The products of fragmentation are focused and analysed via a ToF-mass analyser.

V. Katta, S. K. Chowdhury, and B. T. Chait, Use of a single-quadrupole mass spectrometer for collision-induced dissociation studies of multiply charged peptide ions produced by electrospray ionization, Anal. Chem., 63 (1991) 174-178. 

Figure 2. Workflow of an LC-MS/MS experiment. A mixture of peptides from a protein sample digest is separated by reversed-phase chromatography on a nano-flow HPLC. The peptides elute from the RP column and are ionized by an electrospray source. In the first stage of mass spectrometry, m/z values and charge states for each precursor ion are determined and the most abundant precursor ions are selected for analysis in the second stage. The ions are then fragmented with by collision-induced dissociation (CID) a gas to produce fragment ions which are detected. Using the mass (from MS-1) and sequence information (from MS-2) protein sequence databases are searched to provide peptide identifications and protein matches.

There are three main types of mass analyzers in ESTMS-MS instruments triple quadrupole, ion traps, and quadrupole-time-of-flight (Q-TOF). There are several differences between the mass analyzers in MALDI-TOF and in ESI-MS-MS. Unlike in MALDI-TOF-MS, in ESTMS-MS two mass analyzers are used in tandem to increase the sensitivity of the technique. The peptide ions produced by the ESI sources are carried to the first mass analyzer and only peptides of a set miz ratio are selected. The selected ions are then carried to a collision cell where they are subjected to additional fragmentation to produce smaller amino acid ions using a process called as collision induced dissociation (CID). The CID process employs inert gases such as argon for the dissociation of peptides. These smaller amino acid ions are then resolved in the second mass analyzer before sending to the detector. This process essentially enables highly sensitive detection of actual amino acid sequence of the peptides based on the mIz ratios of individual amino acids. 

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