Scanning, Ion Traps, and Hybrid Mass Spectrometers

Linked Scanning, Ion Traps, and Hybrid Mass Spectrometers 

Diagram showing the relation between the designation MS and the number of sequential fragmentation steps involved. 

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A new generation of linear ion trap mass spectrometers has been developed and exhibits increased performance compared to traditional three-dimensional (3D) ion traps (Hopfgartner et al., 2003 Douglas et al., 2005). A further evolution of the triple-quadrupole family and ion trap class of instruments is the production of the hybrid triple-quadrupole/linear ion trap (QQQ/LIT) platform. Hybrid instruments of this nature allow for operation in space and not just in time when performing MS/MS analysis. This feature allows for increased performance compared to classical ion traps. A powerful combination possible on a hybrid LIT/QQQ instrument is the ability to use highly sensitive and selective precursor ion, constant neutral loss, and multi-MRM as a survey scan for dependent LIT MS/MS. Compared to a simple MS experiment, these comprehensive triple-quadrupole and LIT modes can be more complex to setup. 

Mass spectrometers are used not only to detect the masses of proteins and peptides, but also to identify the proteins, to compare patterns of proteins and peptides, and to scan tissue sections for specific masses. MS is able to do this by giving the mass-to-charge ratio of an ionized species as well as its relative abundance. For biological sample analysis, mass spectrometers are connected to an ionizing source, which is usually matrix-assisted laser desorption ionization (MALDI) [14], surface-enhanced laser desorption/ioni-zation (SELDI, a modified form of MALDI) [15], or electrospray ionization [16]. These interfaces enable the transfer of the peptides or proteins from the solid or liquid phase, respectively, to the gas (vacuum) phase inside the mass spectrometer. Both MALDI and electrospray ionization can be connected to different types of mass analyzers, such as quadrupole, quadruple-ion-traps, time of flight (TOF), or hybrid instruments such as quadrupole-TOF or Fourier transform-ion cyclotron resonance. Each of these instruments can... 

Among these, both LC-MS and LC-MS/MS approaches have been described using different mass analyzers operating in the positive ion mode scan such as triple stage quadrupole (TSQ) mass spectrometers [145, 194, 226, 227, 235, 239, 240, 242-247] and hybrid quadrupole-linear ion trap (LTQ) [173, 193, 218, 238, 241] mass spectrometers working in SRM mode as well as time-of-flight (TOF) [195] and hybrid quadrupole-TOF (Q-TOF) [236,237] mass spectrometers working in the MS mode. 

In terms of mass spectrometry instrumentation, the currently available instruments such as time-of-flight (TOF) analyzers and hybrid quadrupole-TOF analyzers are able to acquire complete mass spectra at rates compatible with fast CE separations. As CE or ultrafast chromatography replaces conventional, slow HPEC applications, TOF-based mass spectrometers will be needed to replace the less efficient scanning types of instruments such as quadrupoles and ion traps for most high-throughput applications. FTICR mass spectrometry remains unsurpassed in terms of resolution and mass accuracy for both MS and MS-MS applications. However, the throughput of FTICR mass spectrometric... 

Sierra Analytics and Applied Biosystems investigated the metabolic profile of indinavir, an HIV protease inhibitor with a very short half-life (2 hours), readily metabolised via CYPs to produce phase I and subsequent II products. Aliquots (10 pL) of indinavir incubated with rat liver S9 fractions were separated by online liquid chromatography and analysed with an Applied Biosystems hybrid triple quadrupole/linear ion trap mass spectrometer in information dependent acquisition (IDA) mode. This consisted of an enhanced MS survey scan followed by enhanced product ion scans for the two most intense parent ions as dependent MS/MS experiments. 

A triple-quadrupole linear ion trap (QqLIT), which is the most widely used hybrid linear ion trap, is based on the ion path of a triple-quadrupole mass spectrometer with Q3 operated as either a conventional RF/DC quadrupole mass filter or a linear ion trap mass spectrometer. " A QqLIT combines the advantages of a QqQ and a QIT within the same platform without compromising the performance of either mass spectrometer. It retains classical QqQ functions such as MRM, product ion scan, precursor ion scan, and constant neutral loss scan for quantitative and qualitative analysis, and possesses MS" ion accumulation... 

Yao M, Ma L, Duchoslav E, Zhu M. Rapid screening and characterization of drug metabolites using multiple ion monitoring dependent product ion scan and postacquisition data mining on a hybrid triple quadrupole-linear ion trap mass spectrometer. Rapid Commun Mass Spectrom 2009 23(11) 1683 1693. 

Recently introduced hybrid triple quadruple—linear ion trap (QTRAP) mass spectrometer has scan functions identical to those of classical triple quadruple (PI scan, NL scan, and MRM). It can be used for small-molecule quantification with MRM in both bioanalysis and in vitro ADME studies (Hopfgartner et ah, 2004). The QTRAP also has scan functions (full MS scan and MS/MS scan) similar to an ion trap mass spectrometer. Most importantly, MS, MRM, PI, and NL scans on QTRAP instruments can serve as survey scans to trigger the information-dependent acquisition (IDA) of enhanced product ion spectra (EPI) with polarity switching, which provide product ion spectra with rich fragments with no low-mass cutoff (Xia et al., 2003 Zheng et al., 2007 Wen et al., 2008b Yao et al., 2008 Jian et al., 2009). The information-dependent acquisitions have been widely applied to reactive... 

Triple Quadrupole Linear Ion Trap Mass Spectrometry Hybrid triple quadrupole linear ion trap (Q-Trap,AB Sciex, Foster City, CA) mass spectrometers provide scan functions identical to those of classical triple quadrupole (MRM, PI, and NL scanning). However, the Q-Trap also has scan functions (full MS... 

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