Orbital ion trap

Fourier-transform (FT) mass analyzers belong to a special class of mass analyzer that detects ions non-destructively and periodically. Therefore, FT mass analyzers are trapping-type instruments. Because periodic and long detection times facilitate accurate ion recognition, FT mass analyzers offer the highest mass resolving power and accuracy of all instruments [23]. The concept of FT-MS was first described by Comisarow and Marshall in the 1970s [24]. The most important types of FT instruments available in the market include ion cyclotron resonance (ICR) [23] and orbital ion trap (orbitrap) [25] mass analyzers. 

Cl, chemical Ionization EESI, electrosonic spray Ionization El, electron ionization ICR, ion cyclotron resonance OIT, orbital Ion trap QqQ, triple quadrupole S, seaor SALDI, surface-assisted laser desorptlon/lonizatlon V-EASI, Venturi easy ambient sonic-spray ionization, n.d.. No data. 

The ions introduced into the trap are maintained on stable orbits applying DC and RF potential to the electrodes. To separate ions, according to their m/z, a RF scan is made. While the RF amplitude increases, ions with higher m/z values are destabilized and they leave the ion trap moving towards the detector. 

The mass-selective instability mode of operation permits the selection and trapping of all ions created over a specified period with subsequent ejection to the detector.26 Ions with different m/z values can be confined within the ion trap and scanned singly by application of voltages that destabilize the orbits of the ions and eject them to the detector. Ion trap instruments interface readily with liquid chromatography, ESI,15 and MALDI.27 The motions of the ions and the dampening gas (e.g., helium) concentrate around the middle of the ion trap, thereby diminishing ion loss through collisions with electrodes. 

Linear combination of atomic orbitals (LCAO) method, 16 736 Linear condensation, in silanol polycondensation, 22 557-558 Linear congruential generator (LCG), 26 1002-1003 Linear copolymers, 7 610t Linear density, 19 742 of fibers, 11 166, 182 Linear dielectrics, 11 91 Linear elastic fracture mechanics (LEFM), 1 509-510 16 184 20 350 Linear ethoxylates, 23 537 Linear ethylene copolymers, 20 179-180 Linear-flow reactor (LFR) polymerization process, 23 394, 395, 396 Linear free energy relationship (LFER) methods, 16 753, 754 Linear higher a-olefins, 20 429 Linear internal olefins (LIOs), 17 724 Linear ion traps, 15 662 Linear kinetics, 9 612 Linear low density polyethylene (LLDPE), 10 596 17 724-725 20 179-211 24 267, 268. See also LLDPE entries a-olefin content in, 20 185-186 analytical and test methods for,... 

FT-ICR detection is accomplished by monitoring the image current induced by the orbiting ion packet as it cycles between the two receiver plates of the ceU. After formation by an ionization event, all trapped ions of a given mIz have the same cyclotron frequency but have random positions in the FT-ICR cell. The net motion of the ions under these conditions does not generate a signal on the receiver plates of the FT-ICR cell because of the random locations of ions. To detect cyclotron motion, an excitation pulse must be applied to the FT-ICR cell so that the ions bunch... 

Ions orbit within trap until ejected by variation in electrode voltage... 

The principles behind an ion trap mass spectrometer are similar to those of the quadrupole mass filter, except that the quadrupole field is generated within a three-dimensional cell using a ring electrode and no filtering of the ions occurs. All of the steps involved in the generation and analysis of the ions take place within the cell, and in order to detect the ions they must be destabilized from their orbits, by altering the electric fields, so... 

An entirely new principle of the ion-trap mass spectrometers is the Orbitrap with a coaxial inner spindle-shaped electrode in an outer barrel-like electrode. The peripheral injected ions move due to their electrostatic attraction to the inner electrode on orbits around and swing simultaneously along the electrode. The frequency of these harmonic oscillations is inversely proportional to the square root of mJz. The detected signals are induced by the frequency of these swings and resulted... 

The quadrupole ion trap (QJT) is about the size of a small fist and consists of a ring electrode and two hyperbolic end electrodes (see March and Todd68 for a detailed theory of operation and history of development). Like the linear ion trap (LIT, see below), the QJT operates at relatively high pressure (10 3 torr) with a helium buffer gas that assists the ions to maintain a stable orbital frequency. The buffer gas also serves as the collision gas for collision-induced dissociation (CID) during MS/MS experiments. 

The heart of a Fourier transform instrument is an ion trap within which ions can circulate in welFdelined orbits for extended pcrit)ds. Such cavilies are constructed to lake advantage of a phenomenon known as /V)/i cychiron resonance. 

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