Trapping type instrument

Trapping-type instrument capable of tandem-in-time experiments and can be linked to ToF analyzer (QIT-ToF). h Trapping-type instrument capable of tandem-in-time experiments and can be linked to Q, FTICFt, or Orbitrap analyzers (e.g., QqLrT-FTICFt, and LIT-Orbitrap). 

Trapping-type instrument capable of tandem-in-time experiments and can be configured to analyze fragments generated externally (e.g., QqFTICR or LIT-FTICR). 

Fourier-transform (FT) mass analyzers belong to a special class of mass analyzer that detects ions non-destructively and periodically. Therefore, FT mass analyzers are trapping-type instruments. Because periodic and long detection times facilitate accurate ion recognition, FT mass analyzers offer the highest mass resolving power and accuracy of all instruments [23]. The concept of FT-MS was first described by Comisarow and Marshall in the 1970s [24]. The most important types of FT instruments available in the market include ion cyclotron resonance (ICR) [23] and orbital ion trap (orbitrap) [25] mass analyzers. 

Tables 6.27 and 6.31 show the main characteristics of ToF-MS. ToF-MS shows an optimum combination of resolution and sensitivity. ToF-MS instruments provide up to 40000 spectra s-1, a mass range exceeding 100000 (in principle unlimited), a resolution of 5000, and peak widths as short as 200 ms. This is better than quadruples and most ion traps can handle. Unlike the quadrupole-type instrument, the detector is detecting every introduced ion (high duty factor). This leads to a 20- to 100-times increase in sensitivity, compared to QMS used in scan mode. The mass range increases quadratically with the time range that is recorded. Only the ion source and detector impose the limits on the mass range. Mass accuracy in ToF-MS is sufficient to gain access to the elemental composition of a molecule. A single point is sufficient for the mass calibration of the instrument. ToF mass spectra are commonly calibrated using two known species, aluminium (27 Da) and coronene (300 Da). ToF is well established in combination with quite different ion sources like in SIMS, MALDI and ESI.

Once a targeted list is assembled, the appropriate LC-MS instrument can be set up to acquire both MS and MS/MS data (or MS" data for traps) in an automated fashion. The MS/MS acquisitions would only be triggered by detection of a targeted precursor ion (from the list) at a minimum specified intensity. Linear ion trap quadrupole instruments are increasingly popular for this type of work (Hopfgartner and Zell, 2005) and are discussed in Chapter 3 of this book. 

Fig. 4 Schematic of an ion trap MS instrument. This device consists of two endcap electrodes (entrance and exit) and a ring electrode. An ion trap MS separates ions based on mass-to-charge ratio (m/z). Once ions are introduced into the ion trap MS, the radiofrequency (rf) amplitude is increased so that ions are sequentially ejected (by increasing mass) and detected. This type of MS provides a routine (i.e., benchtop) and sensitive detector using either GC and LC interfaces. Furthermore, this instrument provides a unique format for multiple stages of MS analysis (MS ). (Courtesy of ThermoFinnigan, San Jose, CA.)...

For the neutral loss scan, the first mass analyzer (Qj) scans all the masses (Figure 7(d)). The second mass analyzer (Q3) also scans, but at a fixed offset from the first mass analyzer. This offset corresponds to a neutral loss that is commonly observed for a particular class of compounds for example, the loss of 44 u (C02) from [M — H] ions will be indicative of carboxylic acids. Alkyl loss (C H2b+i) will be seen in the loss of 15, 29, or 43, etc. and the loss of 18 u (H20) will be indicative of a primary alcohol. A comprehensive table of common neutral fragments may be found in McLafferty and Turecek.32 The mass spectrum is then a record of all precursor ions that lose the specified neutral fragment. Again, neutral loss scans cannot be performed with trap-type MS instruments or with ToF analyzers. However, postacquisition analysis software can be used to search for the specified neutral loss. 

Unlike other typical analytical techniques, such as infrared spectroscopy, ESR measurements require a high level of technical skill and expertise. ESR sample measurements are highly dependent on sample collection, sample preparation, types of solvents, temperature, choice of spin trap, and instrument calibration of electrical and magnetic fields, among other things. 

Unlike beam-type instruments, mass separation in a QIT is achieved by storing the ions in the trapping space and by manipulating their motion in time rather than in space. This task is accomplished with an oscillating electric field that is created within the boundaries of a three-electrode structure. The mass spectrum is acquired by changing the applied rf field to eject ions sequentially from the trapping field. 

Tbe reader new to mass spectrometry is advised to consult an appropriate introductory text [2-9]. A few mass spectrometric terms will be explained here by way of background and to outline the principles of choosing a flame ionization detector, ions are produced in the mass spectrometric detector, but the mass spectrometer is able to analyze these ions further according to their molecular weights or rather, mass-to-charge ratios (m/z, see below) to provide a mass spectrum. Different principles are employed to achieve this in a variety of types of mass spectrometer. The instruments most commonly used in GC—MS are known as magnetic sector, quadrupole and ion trap mass spectrometers. Their differences are not further described here. Bench-top systems are of the quadrupole or ion trap type. 

Since the ESI ion source is compatible with nearly all of mass analyzers in which tandem MS can be performed, a variety of types of mass spectrometers are employed for characterization of lipids. Some examples of the instruments that are used to perform tandem MS include tandem sectors, QqQ, ion-trap, ion-cyclotron resonance, TOF/TOF, and hybrid instruments such as Q-TOF. The majority of tandem MS analyses presented in this part are conducted by using the QqQ-type instrument since majority of the early studies on characterization of lipid species were conducted with this type of instrument, and the characterized fragmentation pattern from this type of instrument can well represent those obtained from other types of instruments even including MALDI-MS [4, 5]. 

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