Q-TOF

This chapter provides brief descriptions of analyzer layouts for three hybrid instruments. More extensive treatments of sector/TOF (AutoSpec-TOF), liquid chromatography/TOF (LCT or LC/TOF with Z-spray), and quadrupole/TOF (Q/TOF), are provided in Chapters 23, 22, and 21, respectively. 

The Q in Q/TOF stands for quadrupole (see Chapter 25, Quadrupole Ion Optics ). A Q/TOF instrument — normally used with an electrospray ion inlet — measures mass spectra directly to obtain molecular or quasi-molecular mass information, or it can be switched rapidly to MS/MS mode to examine structural features of ions. The analyzer layout is presented in Figure 20.2. 

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. 

Schematic diagram of an orthogonal Q/TOF instrument. In this example, an ion beam is produced by electrospray ionization. The solution can be an effluent from a liquid chromatography column or simply a solution of an analyte. The sampling cone and the skimmer help to separate analyte ions from solvent, The RF hexapoles cannot separate ions according to m/z values and are instead used to help confine the ions into a narrow beam. The quadrupole can be made to operate in two modes. In one (wide band-pass mode), all of the ion beam passes through. In the other (narrow band-pass mode), only ions selected according to m/z value are allowed through. In narrow band-pass mode, the gas pressure in the middle hexapole is increased so that ions selected in the quadrupole are caused to fragment following collisions with gas molecules. In both modes, the TOF analyzer is used to produce the final mass spectrum.

Chapter 23 Hybrid Quadrupole Time-of-Flight (Q/TOF) Instruments... 

Scanning techniques are carried out differently with such hybrid instruments as the triple quadrupole analyzer, the Q/TOF (quadrupole and time-of-flight), and double magnetic-sector instruments. 

Q/TOF, used for two mass analyzers (quadrupole and time-of-flight) used in combination QQQ (or QqQ)- a triple quadrupole analyzer (if q is used, it means the central quadrupole is also a collision cell)... 

Q-ToF-LC-MS-MS quadrupole time-of-flight mass analyser in combination with (high performance) liquid chromatography and tandem mass spectrometry... 

As with the Q-ToF instrument, only two types of MS-MS experiment are available with the ion-trap, i.e. the product-ion scan and selected-decomposition monitoring, as described in Sections 3.4.2.1 and 3.4.2.4, respectively. 

The ion-trap and Q-ToF instruments are, because of the way that they operate, unable to carry out precursor-ion scans. Computer manipulation of data generated during product-ion scans of the Q-ToF system, however, can yield equivalent data to that produced directly by precursor-ion scans on other instruments and an evaluation of this software-based approach has been carried out [14],... 

BordoU, R., Hoyes, J., Langridge, J., Chervet, J-P., Vissers, H. and van Veelen, P., Nanobore HPLC-MS and HPLC-MS/MS using a nanoflow ESI interface and a Q-Tof hybrid mass spectrometer . Micromass Technical Note 108, Micromass, Manchester, UK, 1998. 

What is the configuration of a Q-ToF mass spectrometer and what are its anaiyticai strengths ... 

Figure 5.31 LC-electrospray-MS-MS spectrum of the column eluate at around 22 min in the analysis of the peptide mixture from the tryptic digest of glycoprotein TIME-EA4 from silkworm diapause eggs. Reprinted from Bioorg. Med. Chem., 10, Kurahashi, T., Miyazaki, A., Murakami, Y., Suwan, S., Franz, T., Isobe, M., Tani, M. and Kai, H., Determination of a sugar chain and its linkage site on a glycoprotein TIME-EA4 from silkworm diapause eggs by means of LC-ESI-Q-TOF-MS and MS/MS , 1703-1710, Copyright (2002), with permission from Elsevier Science.

Both of the studies involving glycoproteins have employed Q-ToF mass spectrometers and both sets of anthors comment on the sensitivity of this type of instrument, allowing nsefnl data to be obtained from the limited amonnts of sample usually available from natural sources. 

An MS-MS instrument only relatively recently made available commercially for LC-MS applications is the Q-ToF system, i.e. the combination of a quadrupole mass analyser for precursor-ion selection and a time-of-fiight analyser for production detection. As described earlier in Section 3.4.1.4, this instrument has the... 

The structure of Bosentan [30] and three of its metabolites are shown in Figure 5.45 and the product-ion spectra from the [M - - H]+ ions from these compounds in Figure 5.46. All show an ion at m/z 280 which might be assumed, simplistically, to share the same structure. Their accurate masses, determined by using a Q-ToF instrument, however, show that the ions from compounds (1)... 

Q-ToF The combination of quadrupole and time-of-flight mass analysers. This allows the m/z ratios of ions produced during a product-ion scan to be measured accurately and the elemental composition of these ions to be determined. 

Fast atom bombardment (FAB) Plasma desorption (PD) Liquid secondary-ion mass spectrometry (LSIMS) Thermospray (TSP)/plasmaspray (PSP) Electrohydrodynamic ionisation (EHI) Multiphoton ionisation (MPI) Atmospheric pressure chemical ionisation (APCI) Electrospray ionisation (ESI) Ion spray (ISP) Matrix-assisted laser desorption/ionisation (MALDI) Atmospheric pressure photoionisation (APPI) Triple quadrupole (QQQ) Four sector (EBEB) Hybrid (EBQQ) Hybrid (EB-ToF, Q-ToF) Tandem ToF-ToF Photomultiplier... 

Atmospheric pressure chemical ionisation (APCI) MH+ (M - II) M, Q, ToF, FTMS Polar and some nonpolar organics <1 500... 

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