Time-of-flight hybrid instruments

Figure 2.5 Quadrupole-time-of-flight hybrid instrument.

BE-time-of-flight hybrid instruments, enabling high-sensitivity accurate-mass determination of product ions [91-92]. 

Griffiths et al. [36] described the analysis of HETE and diHETE by ESI-MS-MS of [M-H] on a sector-time-of-flight hybrid instrument equipped with a focal-plane detector. The HETE and diHETE could be analysed in underivatized form at the pmol level. The MS-MS spectra allow differentiation of isomeric eicosanoids. 

After the first demonstration of multiply charged gas-phase proteins ions, all major instrument manufacturers developed atmospheric-pressure ion sources, equipped with electrospray interfaces for both protein characterization and LC-MS applications. Within 5 years, electrospray interfacing became the method of choice in LC-MS coupling. It led to a large increase in the use of MS for the characterization and identification of labile and polar analytes as well as to routine quantitative analysis. The advent of electrospray ionization for peptide and protein analysis stimulated further development and analytical application of existing and new mass analysis approaches, such as quadrupole ion traps, Fourier-transform ion-cyclotron resonance MS, and quadru-pole-time-of-flight hybrid instruments. It opened new application areas, such proteomics. LC-MS... 

A variety of tools are available for the detection and characterization of the metabolites. Unless advanced data-acquisition strategies (Ch. 10.4.4) are applied, at least two LC-MS analyses are required. The first injection is performed in full-spectrum LC-MS mode, preferable using an MS system with improved full-spectrum sensitivity, such as (linear) ion trap and time-of-flight (TOP) instruments. The analysis of a blank extract next to real samples greatly facilitates peak detection and avoids further work on endogenous peaks. The data are processed to find the relevant /w/z-values of potential metabolites. These /w/z-values are used as precursor ion m/z in a subsequent (time-scheduled) product-ion LC-MS-MS analysis. Again, instruments with improved full-spectrum sensitivity, such as ion-traps, quadrapole-linear ion trap hybrids (Q-LIT), or quadrapole-TOF hybrids, are favourable. 

In early negative-ion ESI-MS studies, halogenated solvent additives were applied to reduce the risk of discharge formation (Ch. 6.3.2). The use of 1,1,1,3,3,3,-hexafluoro-2-propanol (HFIP) to the mobile phase was proposed for oligonucleotides [22]. This is for instance applied in the rapid characterization of synthetic oligonucleotides by microcapillary LC-MS on a quadrupole-time-of-flight hybrid (Q-TOF) instrument [20]. 

This is true for ion trap hybrids with FT-ICR-MS (see Sect. 4.4.7) and Orbi-trap (see Sect. 4.4.9) instruments, but also for the ion trap-time-of-flight hybrid system. The latter system has been pioneered by the group of Lubman [87, 88]. It has become commercial available for both MALDI and LC-MS applications [89]. All these hybrid MS system are frequently applied in combination with LC and electrospray ionization in, for instance, drag metabolite identification studies and in various proteomics-related studies. 

Time-of-flight (TOF) analyzers have increased the popularity of high resolution MS, either alone or configured as hybrid quadrupole time of flight (QTOF) instruments. TOF provides sensitivity and selectivity somewhere between single stage and tandem MS. 

Hybrid Magnetic-Sector Time-of-Flight (Sector/TOF) Instruments... 

The AutoSpec -TOF hybrid mass spectrometer combines the advantages of a magnetic/electric-sector instrument with those of time-of-flight to give a versatile instrument capable of MS or MS/MS at high or low resolution. 

The term Q/TOF is used to describe a type of hybrid mass spectrometer system in which a quadrupole analyzer (Q) is used in conjunction with a time-of-flight analyzer (TOP). The use of two analyzers together (hybridized) provides distinct advantages that cannot be achieved by either analyzer individually. In the Q/TOF, the quadrupole is used in one of two modes to select the ions to be examined, and the TOF analyzer measures the actual mass spectrum. Hexapole assemblies are also used to help collimate the ion beams. The hybrid orthogonal Q/TOF instrument is illustrated in Figure 23.1. 

A brief description of this hybrid system appears in Chapter 20. For further information on the quadrupole or TOF instruments, see Chapters 25 and 26, Quadrupole Ion Optics and Time-of-Flight Ion Optics. ... 

Commercial mass analyzers are based almost entirely on quadrupoles, magnetic sectors (with or without an added electric sector for high-resolution work), and time-of-flight (TOE) configurations or a combination of these. There are also ion traps and ion cyclotron resonance instruments. These are discussed as single use and combined (hybrid) use. 

This system is very similar to that of a hybrid quadmpole time-of-flight (Q/TOP) instrument but without the initial quadmpole section. 

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