Magnetic/electric-sector

In general terms, the main function of the magnetic/electric-sector section of the hybrid is to be able to resolve m/z values differing by only a few parts per million. Such accuracy allows highly accurate measurement of m/z values and therefore affords excellent elemental compositions of ions if these are molecular ions, the resulting compositions are in fact molecular formulae, which is the usual MS mode. Apart from accurate mass measurement, full mass spectra can also be obtained. The high-resolution separation of ions also allows ions having only small mass differences to be carefully selected for MS/MS studies. 

The AutoSpec -TOF hybrid mass spectrometer combines the advantages of a magnetic/electric-sector instrument with those of time-of-flight to give a versatile instrument capable of MS or MS/MS at high or low resolution. 

Ion Optics of Magnetic/Electric-Sector Mass Spectrometers... 

In a sector instrument, which acts as a combined mass/velocity filter, this difference in forward velocity is used to effect a separation of normal and metastable mj" ions (see Chapter 24, Ion Optics of Magnetic/Electric-Sector Mass Spectrometers ). However, as discussed above, the velocity difference is of no consequence to the quadmpole instrument, which acts only as a mass filter, so the normal and metastable mj ions formed in the first field-free region (Figure 33.1) are not differentiated. 

Magnetic/electric-sector instruments are used to manipulate ion beams by making use of the deflection of charged species (ions) in magnetic or electric fields. 

This focusing action gives an ion beam, in which the m/z values can be measured so accurately that the resolution of a magnetic/electric-sector instrument (separation of ions of different m/z values) is measured as a few parts per million, compared to the more modest few parts per thousand in, say, a quadmpole or ion-trap instrument. 

A magnetic-sector/TOP hybrid has two means of measuring m/z values, one very accurately in a conventional magnetic/electric-sector sense, and the other somewhat less accurately in a time-of-flight sense. 

LC can be combined with all kinds of mass spectrometers, but for practical reasons only quadrapolar, magnetic/electric-sector, and TOP instruments are in wide use. A variety of interfaces are used, including thermospray, plasmaspray, electrospray, dynamic fast-atom bombardment (FAB), particle beam, and moving belt. 

A simple mass spectrometer of low resolution (many quadrupoles, magnetic sectors, time-of-flight) cannot easily be used for accurate mass measurement and, usually, a double-focusing magnetic/electric-sector or Fourier-transform ion cyclotron resonance instrument is needed. 

An accelerator mass spectrometer is not really just an instrument with another type of analyzer, but rather a system that utilizes magnetic/electric sectors to separate ion species. In fact, it can also be looked upon as an ion source. However, we felt it belonged best among the analyzers, because of the way it is utilized. 

Simple considerations of achievable mass resolution and measurement become unrealistic when using electrospray methods of ionization because m/z values change markedly. A substance of mass 10,000 with a single positive charge has an m/z value of 10,000, which is easily measurable with a magnetic/electric sector combination but not with a quadrupole or a TOF instrument. However,... 

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