Mass spectrometry works by combining ion formation, mass analysis, and ion detection. The ways in which mass spectrometer technologies separate ions vary and that is why different mass spectrometers are used for different applications. The choice for a mass spectrometer should be based chiefly on the application, cost, and performance desired.
Among the different types of mass spectrometer technologies, Magnetic Sector Mass Spectrometers are a class of mass spectrometer that uses a static electric or magnetic sector or some combination of the two (separately in space) as a mass analyzer.
In this post you’ll learn three unique facts about Magnetic sector mass spectrometers:
1. How were magnetic sector mass spectrometers commercialized?
Sector field instruments can be considered the longest established type of mass spectrometry technology. Originally, it was also known as a ‘spectrograph’ because photographic plates are used in the detector. Magnetic sector is classified into single or double focusing.
A single focusing magnetic sector mass spectrometer contains only a magnetic sector; this allows the separation of ions based on their masses and kinetic energy (that is why it is considered a momentum analyzer). The achievable mass resolution with this set-up is limited.
In order to achieve higher mass resolution, a double-focusing magnetic sector mass spectrometer is necessary. In this case, the combination of two sectors, a magnetic and an electrostatic one, allows the separation of ions based only on their masses, independent from their kinetic energy.
The first double focusing magnetic sector mass spectrometer was developed by A. Dempster, K. Bainbridge and J. Mattauch in 1936. In the 1950s, the commercially sold mass spectrometers were sector instruments. In the 1950s and 1960s the magnetic sector MS were widely used as they enabled obtaining high-resolution data.
2. Magnetic sector mass spectrometers were used for which applications?
In the early 1930s, mass spectrometers were employed for the development of the first nuclear weapons and for war purposes. After the World War II and until the ‘90s, the commercially developed mass spectrometers were used for research for the petroleum and chemicals industries, and later for pharmaceuticals. In the 90s, mass spectrometers were very expensive, they took up the better part of a lab’s floor space, and labs needed dedicated, doctoral-level staff to operate them.
Although over the years other alternative technologies were introduced, magnetic sector still is the core technology, recognized by official regulations, for dioxin and persistent organic pollutants (POPs) routine analysis. Read more about dioxins and POPs.
As trusted technology, magnetic sector mass spectrometry offers unique technical features:
Mass independent resolution: in a magnetic sector, once the resolution is set, the resolution value is valid for the complete mass range. For example, if the resolution 10.000 is set, each mass has a resolution of 10.000 (e.g. 100 m/z has the same resolution as 1000 m/z). This means that the analytical selectivity is homogeneous over the whole mass range. For all other technologies the resolution value is mass dependent.
Ion separation in space: With given settings in the magnetic sector, the ions are deflected in different paths according to their masses. Settings can be changed so that only one type of ion reaches the detector at the time, without interferences from the other ions.
Mass resolution definition: There are two main definitions for calculating the mass resolution. Only magnetic sector uses the 10% Valley definition, which leads to values which are approximately half of the value for the Full width at half maximum definition (FWHM definition). For example, mass resolution 10.000 with 10% Valley definition corresponds to approximately 20.000 with FWHM definition.
Moreover, sector field instruments typically operate with ion source accelerating voltages in the range of 5.000 to 10.000 Volts. This results in good transmission and with that good sensitivity for high masses.
Do you know more facts about magnetic sector mass spectrometers? Let us know them by sharing in the comments.
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