Magnet, directional focusing

Magnetic analyzer. A direction-focusing device that produces a magnetic field perpendicular to the direction of ion travel. The effect is to bring to a common focus all ions of a given momentum with the same mass-to-charge (m/z) ratio. 

Electrostatic Analyzer In magnetic-sector instruments, an electrostatic sector can be incorporated either before or after the magnet to provide energy resolution and directional focusing of the ion beam. The resolution achievable in these double-focusing instruments is sufficient to separate ions having the same nominal mass (e.g., 28 Daltons) but with different chemical formula (e.g., N2 and CO). 

Fig. 4.18. Direction focusing properties of a 180° magnetic sector on a diverging beam of ions of the same m/z and the same kinetic energy and effect on ions of different m/z- In this illustration, B has to come out of the plane towards the reader for positive ions.

Fig. 4.19. A 90° magnetic sector iUustrating m/z separation and direction focusing in a plane (angles are shown exaggerated). Reprinted from Ref. [1] with permission. American Association for the Advancement of Science, 1979.

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. 

Magnetic sector field equilibr Lorentz force and centrifugal force mv2 n-e-v-B= 2 - direction focusing (lens effect) - separation after m/z (prism effect) 1 500 5 000 TIMS, organic ms, double-focusing sector field ms, tandem ms... 

Figure 16.5—Magnetic analyser mass spectrometer, a) Nier Johnson system, b) directional focusing properties of the magnetic field, c) principle of a double focusing mass spectrometer d) Mattauch-Herzog system.

A J. DEMPSTER develops the electron ionization source and the first spectrometer with a sector-shaped magnet (180°) with direction focusing [17]. 

Magnetic analyser an instrument that causes a direction focusing produced by a magnetic field that is perpendicular to the ions displacement direction. Its effect is to bring to a common focus all the ions of a given momentum. This can be converted to m /z ratios if all the ions have the same kinetic energy. 

The mass spectrometer we now use for zinc analysis, in the laboratory of Maynard Michel of Lawrence Berkeley Laboratory, is a thermal ionization mass spectrometer, a single direction focusing instrument with a 12" radius magnetic sector, double filament, rhenium ionizing source and electron multiplier detector. In addition, have done some preliminary work for Fe and Cu analysis with an automated TI/MS which speeds analysis considerably with excellent precision. We hope to be able to develop methods to use this automated Instrument for zinc analysis as well. 

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