Quadrupole time-of-flight, Q-TOF

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

Currently PCR and mass spectrometry are performed by two separate instruments. However, there is no reason why PCR followed by simple automated cleanup and mass spectrometry cannot be incorporated into a single integrated instrument. Essentially every configuration of the modern ESI mass spectrometer has been used successfully for the analysis of PCR products, from the highest to the lowest resolution involving. Fourier transform ion cyclotron resonance (FTICR), triple quadrupole, quadrupole-time of flight (Q-TOF), and ion trap.22-24 MS discriminates between two structurally related PCR products by MW difference. Mass accuracy is needed to differentiate the... 

Many instrumental set-ups and geometries have been explored. In triple quadrupole mass spectrometry, the first quadrupole selects the parent ion of interest, the second works as a collision cell to fragment the parent ion, and the third isolates the proper product ion. A hybrid type is the quadrupole time-of-flight (Q-TOF) instrument. 

There are three main types of mass analyzers in ESTMS-MS instruments triple quadrupole, ion traps, and quadrupole-time-of-flight (Q-TOF). There are several differences between the mass analyzers in MALDI-TOF and in ESI-MS-MS. Unlike in MALDI-TOF-MS, in ESTMS-MS two mass analyzers are used in tandem to increase the sensitivity of the technique. The peptide ions produced by the ESI sources are carried to the first mass analyzer and only peptides of a set miz ratio are selected. The selected ions are then carried to a collision cell where they are subjected to additional fragmentation to produce smaller amino acid ions using a process called as collision induced dissociation (CID). The CID process employs inert gases such as argon for the dissociation of peptides. These smaller amino acid ions are then resolved in the second mass analyzer before sending to the detector. This process essentially enables highly sensitive detection of actual amino acid sequence of the peptides based on the mIz ratios of individual amino acids. 

In veterinary medicine, boldenone, a synthetic anabolic steroid (Figure 2.1), is commercially available, hence it is a concern in the horseracing industry. Pu et al. (2004) used ion-trap LC-MS analysis to detect boldenone conjugates (sulfate and glucuronide) and their 17-epimers in horse mine after intramuscular administration of boldenone undecylenate. Soon afterwards. Ho et al. (2004) reported the occurrence of endogenous boldenone sulfate in the urine of uncastrated male horses, and quantitated it by quadrupole time-of-flight (Q-TOF) LC-MS-MS. 

The development of ionization techniques and mass analyzers has enabled mass spectrometrists to determine the accurate mass of small molecules as well as biomolecules that are present at low levels. The modem quadrupole time of flight (Q-TOF), Fourier transform ion cyclotron resonance MS (FT-ICR MS), and Orbitrap instruments allow determination of the mass of an ion with accuracies and precisions beyond the decimal point. Mass accuracy measurement, typically measured and reported as parts per million (ppm), is essential for elemental composition assignment. 

A quadrupole time-of-flight (Q-TOF) mass spectrometer incorporates a QMF as the first mass analyzer and a TOF as the second mass analyzer. A collision cell is usually available to facilitate tandem MS. Figure 3.15 illustrates the design of a Q-TOF mass spectrometer that consists of a reflectron TOF mass analyzer in its last stage. Such a setup is similar to QqQ-MS except that QMF II is replaced by the reflectron TOF mass analyzer. When entering... 

FIGURE 14.4 Lithocholic acid methyl ester TMS ether. (A) EI-MS. The [M] ion is at 462, [M-CHs] at 447, [M-TMSOH] at 372, [M-CH3-TMS0]+ at 357, ABCD+ ion at 257, and the ABC ion at 215. (B) GC-APCI-MS profiie. (C) Upper trace GC-APCI-MS and lower trace GC-APCI-MS . The spectrum in (A) was recorded on a singie quadrupole instrument, while (B) and (C) were recorded on a quadrupole time-of-flight (Q-TOF)-type instrument. The MS spectrum was recorded by raising the coiiision energy across the collision ceii but without mass selection. 

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