Magnetron motion

Figure Bl.7.18. (a) Schematic diagram of the trapping cell in an ion cyclotron resonance mass spectrometer excitation plates (E) detector plates (D) trapping plates (T). (b) The magnetron motion due to tire crossing of the magnetic and electric trapping fields is superimposed on the circular cyclotron motion aj taken up by the ions in the magnetic field. Excitation of the cyclotron frequency results in an image current being detected by the detector electrodes which can be Fourier transfonned into a secular frequency related to the m/z ratio of the trapped ion(s).

The motion of this ion results [66] from the superposition of an axial oscillation due to the trapping voltage Vo on the end plates separated by a distance d with frequency (o = (qVo/rnd2)112, a cyclotron motion with frequency o>c = qB/m and a magnetron motion with frequency com = o)2I2[Pg.161]

Cyclotron and magnetron motion. The ions move in an orbit known as the cyclotron movement. But that orbit itself turns around a centre, represented by a black dot, in a magnetron movement, responsible for a loss of resolution. The magnetron motion is the more important, the larger the ion, and thus causes mainly loss of resolution at higher masses. Application of a quadrupolar RF field allows this magnetron movement to be suppressed. 

The trapping of ions generates a further fundamental motion of ions called magnetron motion. Magnetron frequencies are independent of m/z of the ions and are much lower frequencies (1—100 Hz) than cyclotron motion (5 kHz to 5 MHz). Cyclotron motion is characterized by its cyclotron frequency (f), which depends from (i) the magnetic field, (ii) charge of the ion, and (iii) the mass of the ion ... 

Fig. 4.60. Ion motion for co+ = 4c0z and cOz = 8co in an ICR cell. Pure magnetron motion dashed), magnetron plus trapping motion dotted), and the resulting overall motion solid). Reproduced from Ref. [198] by permission. Elsevier Science Publishers, 1995.

Figure 11.4. Plot of an ion undergoing both magnetron and cyclotron motion in the XY plane perpendicular to the magnetic field. For this plot, the slow precession of the magnetron motion (large orbit) is greatly exaggerated over the much higher frequency cyclotron motion (small orbit). (Reprinted from Ref. 161 with permission.)...

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