Transmission quadrupole mass spectrometer

The quadrupole mass filter is the most abundant mass analyser today and RF-only multipoles are used as transmission devices/collision regions in various instrumental configurations. The mass filter is used extensively as a stand-alone mass analyser and as an analyser in multistage mass spectrometers. 

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. 

Particularly for low-mass analytes, sector-based mass spectrometers used in a high-resolution mode can reduce spectral overlaps due to polyatomic ions, thereby improving detection limits compared to those of quadrupole mass spectrometers. However, ion transmission efficiency decreases significantly as the resolution is increased. For example, increasing the resolution provided by the sector mass spectrometer from 300 to 3000 reduces the ion transmission efficiency by about a factor of 14 [127], Further increasing the resolution to 7500 results in another order of magnitude loss in ion transmission efficiency [127]. The use of reaction cells may provide an alternative or complementary means to reduce background due to polyatomic ions. 

A quadrupole is small and relatively inexpensive. It serves as an excellent collision cell for collision activations of ions and ion/molecule reactions. It can also be used as a broadband ion transmission device. A quadrupole is readily coupled with other mass analyzers for MS/MS experiments. One of the most popular configurations is a triple quadrupole mass spectrometer that has found wide applications in LC/MS and LC/MS/MS (see section on Tandem MS). 

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