Quadrupole ion traps and FT-ICR

Ion activation is also accomplished by collisions of the fast-moving precursor ions with a solid surface [12,13]. This ion-surface collision technique, known as surface-induced dissociation (SID), can be implemented on a variety of tandem mass spectrometry systems, such as magnetic sector, TOF, quadrupoles, ion traps, and FT-ICR-MS, by placing a solid surface in the path of the ions [13]. The surface can be a bare metal (e.g., a stainless-steel plate) or a metal covered with self-assembled monolayers [14]. Ion-surface collisions are more efficient in terms of internal energy conversion because of the greater mass of the colliding surface [see Eq. (4.4)]. Consequently, compared to the CID process, in which a serious decrease in the dissociation efficiency is observed, ions of much higher mass can... 

Quadrupole and magnetic-sector instruments are the conunon type of mass analyzers for the detection of the GD-formed ions. The use of quadrupole ion traps, FT-ICR, and TOF instruments has also been explored [11-13], Specifically, quadrupole ion traps and FT-ICR mass spectrometers are of particular interest because they can accumulate and store ions for a desired length of time for subsequent CID or ion-molecule reactions that will eliminate isobaric interferences. The fast-scan facility of a TOF mass analyzer has the advantage that it can be used to monitor even short-lived transient signals. 

These ionization techniques can be combined with a variety of instruments for the sensitive determination of peptide masses. Widely used instruments include triple quadrupole, time-of-flight (TOP), hybrid quadrupole-TOF, TOF-TOF, quadrupole-ion trap, and FT-ICR mass spectrometry. 

Because the irradiating laser beam is pulsed, MALDI is optimally combined with a TOP mass analyzer. The unlimited mass range of TOP and its ability to acquire the entire spectrum from a single laser pulse event are other factors in favor of the MALDI/TOF-MS combination. MALDI-TOF has become a well-known acronym for many researchers. Quadrupole, ion trap, and Fourier transform ion cyclotron resonance (FT-ICR) instruments have also been modified to accommodate MALDI. A schematic diagram of MALDI/TOF-MS is presented in Figure 2.10. A variety of laser systems has found applications in MALDI analysis, and the most common ones use LTV lasers such as the N2 laser (337 nm), the frequency-tripled (355 nm) and frequency-quadrupled (266 nm) Nd YAG laser, and the ArF excimer laser (193 nm). IR lasers have also been used to produce the MALDI effect. The transversely excited atmospheric (TEA) CO2 laser (10.6 p,m), the Q-switched Er YAG laser (2.94 (im), and the CriLiSAF or Nd YAG pumped optical parametric oscillator (OPO) laser (3.28 p,m) are the common IR lasers. UV and IR lasers yield similar spectra for proteins, although better resolution has been obtained for some proteins with an IR laser. 

In both the quadrupole ion traps and the FT-ICR instruments, MS-MS in the product-ion scan mode is feasible, but other scan modes such as neutral-loss and precursor-ion scans are not possible. 

Various analyzers have been used to analyze phenolic compounds. The choice of the MS analyzer is influenced by the main objective of the study. The triple quadrupole (QqQ) has been used to quantify, applying multiple reaction monitoring experiments, whereas the ion trap has been used for both identification and structure elucidation of phenolic compounds. Moreover, time-of-flight (TOF) and Fourier-transform ion cyclotron resonance (FT-ICR) are mainly recommended for studies focused on obtaining accurate mass measurements with errors below 5 ppm and sub-ppm errors, respectively (Werner and others 2008). Nowadays, hybrid equipment also exists, including different ionization sources with different analyzers, for instance electrospray or atmospheric pressure chemical ionization with triple quadrupole and time-of-flight (Waridel and others 2001). 

The majority of H/D studies that have been reported employ quadrupole ion trap (QIT) instruments due to their ease of use, excellent sensitivity, ability to perform MS/MS experiments, compact size, and low cost. Other reports discuss the use of instruments with higher mass-resolving power such as the hybrid QqTOF instruments [47]. A few groups have utilized FT-ICR mass spectrometry, which offers ultra-high mass-resolving power and improved mass accuracy [48, 49]. 

The MALDI-Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (MALDI-FT-ICR-MS) and MALDI-Quadrupole-Ion-trap-TOF Mass Spectrometry (MALDI-QIT-TOF-MS) can be used on IMS. The FT-ICR-MS could provide the high resolution, expansive mass range and high sensitivity imaging MS data and good for determining the elemental composition of small molecules [60],... 

The quadrupole ion trap is seen as a compact and less expensive alternative to FT-ICR mass spectrometers employed for gas-phase metal ion chemical and mass analysis [28,29]. Although lacking the high mass resolving powers available in Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS), the quadrupole ion trap has been investigated by using nonselective and resonance-selective ionization of ablated metal samples. 

There are several types of ionization sources [MALDI, ESI, FAB (fast atom bombardment), PD (Cf-252 plasma desorption), El (electron ionization), Cl (chemical ionization) etc.], different types of mass analyzers [combinations of magnetic and electric sectors, quadrupolar filters (Q) and ion traps (IT), time-of-flight (TOF) and FT-ICR] and different detectors, each with its own advantages and drawbacks. We describe herein only the systems that presently have widespread use for the study of biomolecules ESI coupled to a quadrupole (or triple quadrupole, QqQ) mass analyzer or an ion trap, the MALDI source with the linear or reflectron TOF analyzer, and the FT-ICR system which can be equipped with both ESI and MALDI sources. 

The types of tandem mass spectrometers capable of performing MS/MS experiments fall into two basic categories tandem in space and tandem in time. Tandem-in-space instruments have discrete mass analyzers for each stage of mass spectrometry examples include multisector, triple-quadru-pole, and hybrid instruments (instruments having mixed types of analyzers such as a magnetic sector and a quadrupole). Tandem-in-time instruments have only one mass analyzer where each stage of mass spectrometry takes place in the same analyzer but is separated in time via a sequence of events. Examples of this type of instrument include Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometers and quadrupole ion traps, described in Chapter 3. 

In many respects, the applications of FT-ICR are similar to those of the quadrupole ion trap, as they are both trapping instruments. The major difference is in the ion motion inside the trapping cell and the waveform detection. In recent... 

As with the quadrupole ion trap, ions with a particular m/z ratio can be selected and stored in the FT-ICR cell by the resonant ejection of all other ions. Once isolated, the ions can be stored for variable periods of time (even hours) and allowed to react with neutral reagents that are introduced into the trapping cell. In this manner, the products of bi-molecular reactions can be monitored and, if done as a function of trapping time, it is possible to derive rate constants for the reactions [47]. Collision-induced dissociation can also be performed in the FT-ICR cell by the isolation and subsequent excitation of the cyclotron frequency of the ions. The extra translational kinetic energy of the ion packet results in energetic collisions between the ions and background... 

The mass analyzer is used to separate sample ions. Commonly used analyzers include time-of-flight (TOE), quadrupole (Q), quadrupole ion trap (QIT), and Fourier-transform ion cyclotron resonance (FT-ICR) (9-14). These analyzers provide a wide mass range, high accuracy, and resolution for biomolecular analysis. 

The sample inlet is constituted of a heated fused silica capillary, which is maintained at approximately 200 "C and is encased in a flexible tube. The ion source, in the case of electronic ionization, is composed of electrically heated metallic filaments. Mass analyzers, separating the analytes, include time-of-flight (TOF), linear quadmpole (Q), linear quadrupole ion trap (LIT), quadmpole ion trap (QIT), Fourier transform ion cyclotron resonance (FT-ICR), etc. These detectors differ in their capacity to treat ion beams in a continuous or pulsed (TOF). Quadmpole mass analyzers stabilize and destabilize the ion paths with an oscillating electrical field. A triple quad is more recent technology and consists of three quadmpole stages. Quadmpole ion traps will sequentially eject ions that have been trapped in a ring electrode between two endcap electrodes. 

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