Reversed Nier-Johnson geometry

Figure 5.29 Instrumental setup of a radiofrequency (rf) glow discharge mass spectrometer by combining an ion source developed in house with a commercial double-focusing sector field mass spectrometer with reverse Nier-Johnson geometry (Element, Thermo Fisher Scientific, Bremen, Germany), (f S. Becker et al., IntJ. Mass Spectrom., 164, 81 (1997). Produced by permission of Elsevier.)...

Identification of the different types of ions observed in a mass spectrum through peak-matching and metastable ion analysis allows the determination of molecular structure. Several newer mass spectrometric techniques Mass analysed ion kinetic energy (MIKE) or reversed Nier-Johnson geometry) can also be used in spectral interpretation. These techniques are described in specialised monographs. 

The high-resolution ICP-MS instruments are all based on a reverse Nier-Johnson geometry with an electrostatic and a magnetic analyzer [14,20]. The routinely observable resolution is between 3000 and 10 000 m/Am. This resolution is sufficient for the resolution of a number of molecular ion interferences such as ArO+ on 5<%e and ArCl+ on 75 As as prominent examples. Other molecular ion interferences are still not resolvable. 

Therefore through peak-matching and metastable peak analysis, it is possible to determine with great confidence the structure of the ions. However the latter procedure has become a little out-dated when compared with the new and more efficient techniques (e.g. MIKE or reversed Nier-Johnson geometry), described in specialized monographs. 

Figure 9.21 The reverse Nier-Johnson geometry of the Thermo Scientific Element with a GD source. ( Thermo Fisher Scientific, www.thermofisher.com. Used with permission.)...

Figure 14. Double focusing MS (reversed Nier-Johnson geometry)...

Figure 2.11 Double-focusing setup (reverse Nier-Johnson geometry see below), illustrating how the dispersion of the first sector is compensated for by that of the second sector. Ions with the same mass-to-charge ratio, but a difference in kinetic energy and/or direction, are still focused to one point. Owing to the possibility of using a wider slit between the two sectors thus created, a lower loss in ion transmission efficiency is realized.

Figure 2.184 Principle of the double focussing magnetic sector mass spectrometer (reversed Nier Johnson geometry BE).

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