ABSTRACT
The advantages of a linear ion trap (LIT) compared to the conventional threedimensional quadrupole ion trap (3D QIT) have been discussed in several reports [1-3], in which higher ion trap capacity and higher trapping efciency of the LIT compared to those of 3D QIT are described. An LIT consists of multipole rod electrodes and end-cap electrodes, wherein radial resonant excitation in the quadrupole potential enables the mass-selective isolation, activation, and ejection of ions [2,3]. In particular, mass-selective ejection techniques are important practically because they enhance instrument sensitivities by over 10 times that of the conventional 3D QIT [3]. Linear ion traps (LITs) have been incorporated in tandem not only with standalone ion traps, but also in hybrid instruments with analyzers such as time-of-ight mass spectrometers (TOF-MS) [4,5], orbitrap mass spectrometers [6], and Fourier transform ion cyclotron resonance mass spectrometers (FT-ICR-MS) [7], and these have had a huge impact on mass spectrometry.*
12.1 Introduction ................................................................................................ 573 12.2 Geometry and Mass-Selective Characteristics of the AREX LIT ............. 575 12.3 Hybrid Mass Spectrometers combined with the AREX LIT ..................... 579
12.3.1 Duty Cycle Enhancements of the Orthogonal-Acceleration Mass Spectrometer ........................................................................ 580
12.3.2 Two-Dimensional Mass Spectrometry .......................................... 582 12.4 Ion Fragmentation in the AREX LIT ......................................................... 583
12.4.1 Collision-Induced Dissociation ..................................................... 584 12.4.2 Electron-Capture Dissociation ...................................................... 587
12.5 Conclusions ................................................................................................. 588 References .............................................................................................................. 589
There is no axial potential in the middle of the rod assembly in the original types of LIT, however, multipole rod electrodes with an axial potential were developed by the following groups. Gerlich developed an LIT with an additional cylindrical electrode around the rods by which an axial DC potential was formed [8]. This arrangement enabled the connement of ions in a limited region inside the array of multipole rod electrodes. Thomson and coworkers have developed many variations of multipole rod electrodes with a unidirectional potential along the rod axis for a collision cell. These comprise the use of segmented rod sets [9], conical rods [10], and rods with additional electrodes (T-rods) [11], which are now called the LINACTM.*
In an ion guide with a unidirectional potential, ions pass through much faster than in the absence of an axial eld. Since the ions are ejected from the collision cell within a few milliseconds, high-speed switching between different forms of MS/MS analysis (for example, multiple reaction monitoring (MRM) and selected-ion monitoring (SIM)) is possible. Recently another type of collision cell, which has a unidirectional potential, was also reported [12], where the axial potential was formed from the resistive coating on the surface of the rod electrodes.
