Cyclotron resonance frequency

Jeffries, J. B. Barlow, S. E. Dunn, G. H. Theory of space-charge shift of ion cyclotron resonance frequencies. Int. J. Mass Spectrom. Ion Phys. 1983,54,169-187. 

Fig. 4.49. Motion of positive ions in a uniform magnetic field B. (a) The radius is a function of ion velocity, but the frequencyof circulation is not. (b) Excitation of the ions by an RF electric field oscillating at their cyclotron resonance frequency. Adapted from Ref. [196] by permission. John Wiley Sons, 1986.

Hippie, Sommer and Thomas devised a mass spectrometer of new design to determine the Faraday by measuring the cyclotron resonance frequency of protons in a known magnetic field. Recognizing that this device measures co, the cyclotron frequency, Hippie, Sommer and Thomas proposed the name omegatron. 

When the region belwceii the plates in Figure 20-17 contains an ensemble of ions of the same mass-to-eharge ratio, application of the ac signal having the cyclotron resonance frequency sets all of the particles into coherent motion in phase with the field. Ions of different cyclotron frequency, that is, those with different mas.s-to-charge ratios, are unaffected by ihc ac licid. 

FIGURE 6.3 The time-of-flight of the ions versus the quadrupolar excitation frequency. The cyclotron resonance frequency is determined from the position of the dip. 

The RF quadrupole trap and the Penning trap can be used not only to trap ions but also to perform very precise measurements of their masses [1219]. Unlike other mass spectrometers, the signal is not obtained from mass-selected particles impinging on the detector, but from an induction voltage picked up by external electrodes from the ion motion. Fourier analysis of this signal gives the frequencies of the three components. Since the cyclotron resonance frequency... 

The extra energy of the ion has to come from somewhere. It comes in fact from the accelerating field. If, therefore, we vary the frequency of the applied field, we will observe absorption of energy when the frequency coincides with the cyclotron resonance frequency of the ion. If we plot the absorption of energy as a function of frequency, we will then get a typical... 

An ion cyclotron resonance (ICR) spectrometer creates a pulse of ions in a magnetic field. These are brought into resonance by scanning the applied radiofrequency. From the cyclotron resonance frequency and the magnetic field strength the mlz ratio can be calculated. The use of a fast Fourier transform (FT-ICR) refines the method. 

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