MS in Ion Trap Instruments

However, the process can also be considered in more general terms (Fig. 4.5) one starts with the population of ions, from which the precursor ion is selected, excited, and fragmented, resulting in a new population of (product or daughter) ions. The latter population can either be scarmed out to be detected, or can serve in a new 

Currently, ion trap MS instmments are primarily used for analytical applications, i.e., in combination with GC or LC in, among other, enviromnental, food-safety, chnical, pharmaceutical, or biochemical apphcation areas. In many of these applications, the potential of multistage-MS plays an important role. The acquisition of fragmentation trees enables detailed study on the fragmentation behavior of target compounds and/or compound classes, e.g., [67]. 

However, ion trap MS can also be apphed in more fundamental ion chemistry studies [68], especially because the reaction time can be varied over several orders of magnitude. Due to the He bath gas in the ion trap, the pressure in the ion trap is several orders of magnitude higher than in an FT-ICR cell, but much lower than in high-pressure MS and FA-MS. 

Giving the residence time of ions in the trap, one may anticipate that ion-molecule reactions would readily take place in the ion trap. In fact, self-protonation of several compounds, present at higher concentrations in the ion trap, was observed 

It allows reaction products to be observed from reactions under either kinetic or thermodynamic control. Numerous reports are available, where ion trap MS is applied in ion chemistry studies [68], e.g., involving reactions between 1,4-benzodiazepines and dimethyl ether ions [77], dissociation of [Alanine + Alkali cation]+-ions to study the role of the metal cation [78], or regioselective ion-molecule reactions to enable MS differentiation of protonated isomeric aromatic diamines [79]. The three-dimensional ion trap mass spectrometer has even been described as a complete chemical laboratory for fundamental gas-phase studies of metal-mediated chemistry [80]. 

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In an FT-ICR instrument, which also is an ion-trapping device, MS-MS can be performed in a manner similar to MS-MS in ion-trap instruments. However, fragmentation by collisions is generally much less effective because of the significantly lower pressures in the FT-ICR cell this is only partially compensated for by the longer ion residence times that are achievable. 

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