RF-Only Ion Guides and LIT Mass Spectrometers

The trapping dimensions in QlTs and LITs are essentially simple harmonic oscillators, at least near the center of the traps. Because of this, in addition to trapping fields, ions have their own resonant frequencies inside the trap which can be used to resonantly excite them to high-excnu-sion trajectories and to manipulate the ion populations to a degree surpassed only by FTICR instruments. Because of this, Qrr mass spectrometers are extremely flexible in MS/MS experiments. 

Similar to FTICR mass spectrometers, ions in LITs and QlTs have resonant modes whereby their trajectories can be excited by the application of low-ampHtude resonant frequencies on the endcaps (for QIT-MS) or quadrupole rods (for 

LIT-MS). This means that the SWIFT technique can also be applied selectively to excite and/or eject ions from the trap. For a better description of the SWIFT method, see Section 2.5.1. 

Although photodissodation has also been performed extensively on QIT inshu-ments [102-110], the results have not been so widely useful that the method has been implemented on commercial systems. There are two reasons for this (i) the excursion paths of ions in QIT instruments is often wider than the laser beams, so that some ions may not be irradiated and (ii) with IRMPD in particular, where hundreds to thousands of photons must be absorbed in order to heat the molecules up for dissociation, ions experience a competition between heating (from the laser) and coohng (from collisions and blackbody radiation). At 10 mbar, the collisional 

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