Magnetic sector field instruments

Two types of commercial magnetic sector field instrument will be described in the following ... 

Magnetic sector field instruments have mass resolutions up to m/Am = 20000 quad-rupole instruments are limited to a mass resolution of approximately m/Am = 500. For both types of instrument the a mass range extends to 500. 

Ions formed in an electron ionization mass spectrometer possess a relatively low initial energy spread, therefore single focnsing magnetic sector field instruments are sufficient to separate ion beams with different m/z ratios. Commercial stable isotope ratio mass spectrometers (SIRMS) allow highly precise and accnrate isotope ratio measnrements e.g., with the Finnigan MAT 253, of H/D, C/ C, N/ N, 0/ 0, jQj and SFg) Si/ Si as weU as Ar, Kr and... 

Wittmaack K (2011) Accurate in situ calibration of the energy bandwidth and the zero-energy offset in SIMS analysis using magnetic sector field instruments. Int J Mass Spectrom 300 65-69. doi 10.1016/j.ijms.2010.12.009... 

Accomplishment of high mass resolution in double-focusing magnetic sector field instruments... 

Apart from the quadrupole and TOP analyzers described in Sect. 3.2.2, the most important types of mass analyzer used in common dynamic SIMS instruments employ a magnetic-sector field. 

Fig. 3.19. Basic set-up of a direct imaging magnetic sector instrument. The stigmatic secondary ion optics consists of an electrostatic analyzer (ESA) and a magnet sector field.

The most commonly used mass separators are quadrupoles, ions traps and time-of-flight analyzers, for which the principle of mass separation is discussed below. Additionally, other types such as magnetic sector field or Fourier-trans-form cyclotron-resonance instruments are available. 

A quite different type of mass spectrometer - the first 180° magnetic sector field mass spectrometer (see Figure 1.7), with directional focusing of ions for isotope analysis, was constructed by Dempster, independently of other instrumental developments in mass spectrometry, in 1918. 

Double-focusing mass spectrometers with high mass resolution are rather bulky and expensive instruments so that the development of single magnetic sector field mass spectrometers was of significance in the following years. 

The combination of an electric sector field with a magnetic sector field to form a double-focusing instrument is advantageous for improving the properties (e.g., the mass resolution) of 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. 

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