Ion isolation

In FT-ICR mass spectrometers, ion isolation and detection occur in the same region. In fact all ions coming from the source are simultaneously excited applying a RF pulse of a... 

Under commonly used reaction conditions, the intermediate species is indicated to be a quasiphosphonium ion. Isolation of the intermediates from reactions in which the initial substrate is sufficiently reactive not to require heating, thereby precluding the second step from occurring rapidly, has provided evidence (nuclear magnetic resonance [NMR] and x-ray) of a quasiphosphonium ion species rather than a phosphorane species.17-26... 

The supplementary RF voltage may also be set to contain all frequencies but a narrow band, corresponding to a narrow m/z range, forcing all ions outside this range to leave the trap. This mode of operation is usually referred to as ion isolation, and is the first step when performing MS/MS (see below). 

There is no justification for such a classification of ion stabilities outside the mass spectrometer because almost all ions created under the conditions inside a mass spectrometer would spontaneously react in the atmosphere or in solvents. Nevertheless, this classification is useful as far as ions isolated in the gas phase are concerned and is valid independently of the type of mass analyzer or ionization method employed. 

Wuhrer, M., Balog, C. I., Koeleman, C. A., Deelder, A. M., and Hokke, C. H., New features of site-specific horseradish peroxidase (HRP) glycosylation uncovered by nano-LC-MS with repeated ion-isolation/ fragmentation cycles, Biochimica et Biophysica Acta 1723(1-3), 229-239, 2005. 

SWIFT excitation affords another method of resonance selection or ejection and has been applied in ICP-IT-MS by C. I. Frum to effect both ion isolation and collision-induced dissociation of ions sampled from an ICP [58]. An example of the isolation of 142Ce from a mixture containing all the lanthanide isotopes is shown in Fig. 9.14. In the absence of SWIFT excitation (Fig. 9.14a) space charge effects on both the lanthanides and Y+ are evident (space charge for Th+ is reduced by the prior ejection of lighter ions during the mass scan). Space charge effects are eliminated on application of SWIFT ion isolation. 

Shibata et al. (213) prepared and screened an SP oligopeptide library for its ability to complex cobalt ions, isolating several high-binding sequences. 

Co (H2NC2H4)2NH 2] ion, isolated as the dark brown, crystalline tri-iodide... 

A still greater effect can be achieved if structural modifications, exhibiting more efficient central ion isolation and more efficient energy transfer from ligand to metal can be found (for example, as described in Ref. 380, the Cs-nonsymmetric clathrochelate [Eu(bpy.bpy.bpz)]5+ cation demonstrated substantial increases in both lifetime and quantum yield compared with other complexes of this type). 

The infrared spectrum of the N02 ion isolated in an argon matrix was studied by Milligan et al. (4) and Milligan and Jacox... 

Decomposition of the acetate ion isolated in a potassium iodide matrix was studied [38] (753 to 847 K) by infrared measurements of the quantities of acetate or formate (product) ions present. Reaction, suggested to be controlled by the step ... 

Identifications from on-tissue without enzymatic digest have been reported (52,53). However, the approach is limited to low mass proteins due to the fact that ion isolation and collision-induced dissociation, as used in commercial MSI instruments, allow reliable and accurate selection and fragmentation of... 

The three steps of an MS/MS experiment are performed by DIT using an approach substantially different from that employed in 3D IT or linear ITs (Ding, 2004). In those cases, the precursor ion isolation is performed by applying one or more dipole excitation waveforms, with a maximum isolation resolution of -1300 (expressed as the isolation mass divided by the baseline width of the isolation window). In the case of DIT, ion isolation is performed by sequential forward and reverse scans, so as to eject all ions with m/z values lower and higher than that of interest, respectively. This method can provide precursor ion isolation with a resolution >3500. 

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