Magnetic-Sector Tandem Mass Spectrometers

A major advantage of these sector instruments is that all four types of scan functions (Section 4.2) can be implemented. Multisector instruments also have the facility to perform MS experiments. The number of stages, n, of MS analysis is, however, restricted to the number of sectors in that tandem instrument. In addition, the charge-permutation reactions of fast-moving species, mentioned in 

Tandem MS Scans for Magnetic-Sector Instruments In magnetic-sector instrnments, fragmentation reactions that occur in the FFRs in front of an electric or a magnetic analyzer are monitored by using specifically designed scan laws [37]. 

The B-Scan. If the precnrsor ion fragments in front of a magnetic analyzer, the resnlting fragment ion will not be detected at its true mass values but 

Scanning the magnet field strength provides the product-ion mass spectrum. The product-ion peaks are broad and of low intensity. 

E-scan. If the precursor ion fragments in front of an electric sector, the kinetic energy of the resulting product ion is lower than its precursor, owing to the fact that the velocity of the product ion is conserved but its mass is reduced. The newly formed ion mi can be transmitted through the electric sector only after the electric field Ep is reduced commensurately to a new value Ei, according to 

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CAD spectrometer collision activated dissociation EBE spectrometer electric sector - magnetic sector-electric sector tandem mass spectrometer... 

Magnetic sectors can be used on their own, or in conjunction with energy analysers to fomi a tandem mass spectrometer. The unique features of the reverse geometry instrument are presented from this point. 

A single magnetic sector can be used as a mass filter for other apparatus. However, much more infonnation of the simple mass spectrum of a species can be obtained using the tandem mass spectrometer. 

ToF mass spectrometers as dynamic instruments gained popularity with the introduction of matrix assisted laser desorption/ionization (MALDI) and electrospray ionization (ESI) as effective pulsed ion sources for the soft ionization of large biomolecules (up to 10s dalton) due to their high ion transmission.38 ToF mass spectrometers, quadrupole analyzers and/or magnetic sector fields can be combined in tandem mass spectrometers (MS/MS) for the analysis of organic compounds. 

Instruments that incorporate two or three mass analysers in a series have been developed to study ion fragmentation. Several of the same type of mass analyser can constitute a tandem mass spectrometer, or they can be constructed using different mass analysers (hybrids). Hybrid spectrometers include the combination of magnetic sector followed by quadrupole, multiple quadrupole, quadrupole TOF, etc. In these instruments, a collision cell is placed between each analyser (Fig. 16.23). Tandem instruments have different scanning modes. 

The most common types of MS/MS instruments available to researchers in food chemistry include triple quadrupole mass spectrometers and ion traps. Less common but commercially produced tandem mass spectrometers include magnetic sector instruments, Fourier transform ion cyclotron resonance (FTICR) mass spectrometers, and quadrupole time-of-flight (QTOF) hybrid instruments (Table A.3A.1). Beginning in 2001, TOF-TOF tandem mass spectrometers became available from instrument manufacturers. These instruments have the potential to deliver high-resolution tandem mass spectra with high speed and should be compatible with the chip-based chromatography systems now under development. 

Two magnetic sector instruments have also been operated in tandem, with a collision ceil placed between the two instruments. These instruments permit high resolution selection of both parent and product ions. However, these mstruments are now rarely used as they are expensive and cumbersome to operate. Double focusing mass spectrometers can also be used as tandem mass spectrometers by a technique known as linked scanning. A product ion scan by linked scanning involves low resolution for MSI and high resolution for MS2,... 

The types of tandem mass spectrometers capable of performing MS/MS experiments fall into two basic categories tandem in space and tandem in time. Tandem-in-space instruments have discrete mass analyzers for each stage of mass spectrometry examples include multisector, triple-quadru-pole, and hybrid instruments (instruments having mixed types of analyzers such as a magnetic sector and a quadrupole). Tandem-in-time instruments have only one mass analyzer where each stage of mass spectrometry takes place in the same analyzer but is separated in time via a sequence of events. Examples of this type of instrument include Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometers and quadrupole ion traps, described in Chapter 3. 

Sector instruments and hybrid quadrupole-scctor instruments have also been u>od in a tandem manner. The first tandem mass spectrometers were sector instruments that combined an electric sector speciromc-ler with a magnetic sector spccironieier. cither in forward geometry (electric sector followed by magnetic... 

Tandem mass spectrometers have been built with three quadrupoles as shown in Fig. 9.23, and with other combinations of sector and TOF mass analyzers. Electric and magnetic sector analyzers have been combined with quadrupoles and with TOF analyzers. 

TCID experiments employ tandem mass spectrometers of various types. Guided ion beam (GIB) instruments use a radio frequency octopole in the interaction region for high-efficiency collection of scattered products and low-energy ions. These instruments typically use a magnetic sector or Wien filter for initial mass analysis and... 

A scan in a tandem mass spectrometer with two or more mtz analysers e.g a triple quadrupole or a sector mass spectrometer that incorporates at least one magnetic sector and one electric sector. Two or more of the analysers are scanned simultaneously so as to preserve a predetermined relationship between scan parameters to produce a product ion, precursor ion or constant neutral loss or gain spectrum. 

FIGURE 7 Tandem mass separator. Sample ions enter mass selector 1, where the parent ions are separated. The selected ions next enter the collision chamber, where they collide with gas molecules to form the daughter ions, which are finally separated in the mass selector 2 and expelled for detection. Either magnetic sector or quadrupole mass analyzers or both types mixed can make up a tandem mass spectrometer. A single ion trap can also function as a tandem mass spectrometer performing the same processes as described above in the same location but in consecutive steps. 

The electrospray and continuous flow-FAB experiments were carried out on a Finnigan-MAT TSQ700 triple quadrupole low resolution tandem mass spectrometer and a JEOL four sector HXllO/HXllO magnetic high resolution tandem mass spectrometer, respectively. The electrospray ionization source was manufactured by Analytica of Branford, CT. The MALDI experiments were done on a Vestec-2000 time-of-flight mass spectrometer equipped with a nitrogen laser. Chromatographic purifications of standards were performed on Applied Biosystems HOB microbore HPLC systems. 

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