Nier-Johnson geometry

Another famous type of EB arrangement has become known as Nier-Johnson geometry (Fig. 4.23). [75] Here, the ion beam first passes through the electrostatic... 

Fig. 4.23. Nier-Johnson geometry (EB). [75] Direction and velocity focusing are shown exaggerated. Reprinted from Ref. [1] with permission. American Association for the Advancement of Science, 1979.

The most recent metastable defocusing technique, which is referred to as mass-analyzed ion kinetic spectroscopy (MIKES) by Beynon (77, 270, 277) and as direct analysis of daughter ions (DADI) by Maurer (278) requires the interchange of the source and collector positions in a double-focusing mass spectrometer of Nier-Johnson geometry. With... 

Figure 3.5 Double-focusing sector field mass spectrometer with Nier-johnson geometry. (77. Kienitz (ed.), Massenspektrometrie (1968), Verlag Chemie, Weinheim. Reproduced by permission ofWiley-VCH)...

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.)...

For a Nier-Johnson geometry, ions following a trajectory with radius R, imposed by the analyser tube, will be detected. Hence, to obtain a spectrum within a given mass range, the field B has to be progressively modified (or scanned). In the scanning mode, all ions, irrespective of their m/z value, will successively follow the unique path that leads to the detector. 

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. 

Figure 9 IMS-3f, improved stigmatic ion microscope, Nier-Johnson geometry.

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