Magnetic sector analyzer tandem

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. 

All four types of scan laws discussed in Section 4.2 can be implemented with a triple-quadrupole instrument. For example, to acquire a product-ion spectrum, Qi is set to transmit ions of a specified miz value into Q2, where they undergo a CID process. Q3 is scanned to mass-analyze the products formed in Q2. A precursor-ion spectrum is acquired by reversing this procedure that is, Q3 is set to transmit just the m/z value of a desired product ion, and Qi is scanned to transmit all precursors of this chosen product ion. As compared to the magnetic sector-based tandem instruments, a simple scan law is used in the triple-quadrupole instruments to monitor the loss of a neutral. The fields of Qi and Q3 are both scanned in tandem, but with an offset value related to the mass of the neutral. 

An AutoSpec-TOF mass spectrometer has a magnetic sector and an electron multiplier ion detector for carrying out one type of mass spectrometry plus a TOF analyzer with a microchannel plate multipoint ion collector for another type of mass spectrometry. Either analyzer can be used separately, or the two can be run in tandem (Figure 20.4). 

The most common modes of operation for ms/ms systems include daughter scan, parent ion scan, neutral loss scan, and selected reaction monitoring. The mode chosen depends on the information required. Stmctural identification is generally obtained using daughter or parent ion scan. The mass analyzers commonly used in tandem systems include quadmpole, magnetic-sector, electric-sector, time-of-flight, and ion cyclotron resonance. Some instmments add a third analyzer such as the triple quadmpole ms (27). 

Different mass analysers can be combined with the electrospray ionization source to effect analysis. These include magnetic sector analysers, quadrupole filter (Q), quadrupole ion trap (QIT), time of flight (TOF), and more recently the Fourrier transform ion cyclotron resonance (FTICR) mass analysers. Tandem mass spectrometry can also be effected by combining one or more mass analysers in tandem, as in a triple quadrupole or a QTOF. The first analyzer is usually used as a mass filter to select parent ions that can be fragmented and analyzed by subsequent analysers. 

It should be pointed out that FAB, MALDI, and ESI can be used to provide ions for peptide mass maps or for microsequencing and that any kind of ion analyzer can support searches based only on molecular masses. Fragment or sequence ions are provided by instruments that can both select precursor ions and record their fragmentation. Such mass spectrometers include ion traps, Fourier transform ion cyclotron resonance, tandem quadrupole, tandem magnetic sector, several configurations of time-of-flight (TOF) analyzers, and hybrid systems such as quadrupole-TOF and ion trap-TOF analyzers. 

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. 

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. 

Pyrolysis Tandem Mass Spectrometry. Details of the instrument have been described (10). Pyrolysis conditions were similar to those used for the PMS instrument. The pyrolysate was ionized at 70 eV and ions of interest were selected in the first magnetic sector (resolution 500). These ions were dissociated by collision with helium atoms (pressure 0.9 Pa), accelerated at 15 kV and analyzed in a second magnetic sector. Ions were detected by simultaneous ion detection using channel plates, a phosphor screen and a diode array camera. Total analysis time for each ion is 8 s. 

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]. 

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