Quadrupole orthogonal time-of-flights

Plumb, R. Castro-Perez, J. Granger, J. Beattie, L Joncour, K. etal. Ultraperformance liquid chromatography coupled to quadrupole-orthogonal time-of-flight mass spectrometry. Rapid Commun Mass Spectrom 2004, 18, 2331-2337. 

In this instrument, the final stage of the triple quadrupole is replaced by an orthogonal time-of-flight (ToF) mass analyser, as shown in Figure 3.10. The configuration is typical of the latest generation of ToF instruments in which a number of reflectrons, in this case two, are used to increase the flight path of the ions and thus increase the resolution that may be achieved. 

The rapid LC methods employed for array analysis produce typical peak widths at half-height of less than 2 s. It was immediately apparent that the scan rates achievable on a radiofrequency (RF) quadrupole mass spectrometer would not be sufficient to generate high-quality mass spectra that could be used to confirm the presence of a desired chemical entity. Alternatively, commercial orthogonal time-of-flight (TOF) mass spectrometers can acquire full scan profile data at rates approaching 10 Hz so that rapid switching between up to four streams becomes feasible. Therefore this approach was followed in our development of the novel interface based on the Micromass LCT instrument. 

Once ions are produced, they are typically directed into a mass analyzer, where the ions are separated by their mass-charge ratios and detected. The types of mass analyzers vary widely.By far, the most common is the time-of-flight mass analyzer due to its simplicity and the pulsed nature of ion extraction from the ion source, which makes it especially compatible with pulsed laser excitation, but laser desorption/ionization sources have been coupled to quadrupoles, electromagnetic sector instruments, orthogonal time-of-flight mass spectrometers, quadmpole ion traps, Fourier transform mass spectrometers, and even the recently introduced Orbitrap. Detailed discussion of these mass analyzers is beyond the scope of this chapter but is not out of the scope of other chapters in this volume and elsewhere. However, laser desorption ion sources produce ions with a particular momentum and temperamre, and great care must be taken in coupling these ion sources to the mass spectrometers so that the ions momentum and temperature parameters are compatible with the instrument at hand. 

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. 

Py/GC/MS. pyrolysis, gas chromatography, and mass spectrometry used as a combined technique Py/MS. pyrolysis and mass spectrometry used as a combined technique oa-TOF. orthogonally accelerated time of flight Q. quadrupole field or instrument... 

Figure 5.45 Structures of (1) Bosentan (C27H29N5O6S [M + H]+ 552.1917) and three of its metabolites, formed by (2) oxidation (C27H29N5O7S [M + H]+ 568.1866), (3) demethylation (C26H27N5O6S [M- -H]+ 538.1760), and (4) demethylation-oxidation (C26H27N5O7S [M + M]+ 554.1709). Reprinted by permission of Elsevier Science from Exact mass measurement of product ions for the structural elucidation of drug metabolites with a tandem quadrupole orthogonal-acceleration time-of-flight mass spectrometer , by Hopfgartner, G., Chemushevich, I. V., Covey, T., Plomley, 1. B. and Bonner, R., Journal of the American Society for Mass Spectrometry, Vol. 10, pp. 1305-1314, Copyright 1999 by the American Society for Mass Spectrometry.

Morris H.R., Paxton T., Dell A., Langhome J., Berg M., Bordoli R.S., Hoyes J., and Bateman R.H. (1996), High sensitivity collisionally-activated decomposition tandem mass spectrometry on a novel quadrupole/orthogonal-acceleration time-of-flight mass spectrometer, Rapid Commun. Mass Spectrom. 10, 889-896. 

Bobeldijk, I., J.P.C. Vissers, G. Kearney, et al. 2001. Screening and identification of unknown contaminants in water with liquid chromatography and quadrupole-orthogonal acceleration-time-of-flight tandem mass spectrometry. J. Chromatogr. A 929 63-74. 

Scheme of a hybrid mass spectrometer including a quadrupole analyser, a quadrupolar collision cell and an orthogonal acceleration time-of-flight analyser. 

Hoyes, J. B., Jones, C., Langridge, J. I., Miliar, A., Vissers, J. P. (2002). A novel precursor ion discovery method on a hybrid quadrupole orthogonal acceleration time-of-flight (Q-TOF) mass spectrometer for studying protein phosphorylation. 

---