Magnetic and Electrostatic Field Ion Cyclotron Resonance ICR Analyzers

Interactions with a magnetic and electrostatic field ion cyclotron resonance (ICR) analyzers 

Similarly to the magnetic analyzer, ion separation is based on the circular motion of a charged species in a magnetic field in ICR instruments as well. The difference is that in the ICR, ions undergo several full cycles in the ICR cell. Other differences, such as the application of electrostatic trapping fields, are also crucial and the ion motion is, in fact, much more complex than implied by the simplified discussion below. For the technically inclined reader, we recommend the book by Marshall and Verdun [42]. If only ions with the same mtz ratios are present, such as indicated in Fig. 20, ion motion can be related to a regular sine function, the frequency of which (co) is inversely proportional to the mtz ratio  

Note that Equation (21) is just a different representation of Equation (18). 

It is easy to picture that if ions with different m z ratios are present, circular motions with different frequencies (coj) are detected. Therefore, the detected signal will be a combination of sine functions with different w, frequencies (i.e., m z ratios) and amplitudes (A ) that are related to ion intensities. Such a complex signal is shown in Fig. 21a. This signal is then deconvoluted by using the well-known Fourier transformation and the corresponding mass spectrum is obtained (Fig. 21b). Owing to this relationship between an ICR signal and Fourier transformation, the term FT-ICR instruments is often applied. 

Note that in contrast to a sweeping detection of ions in magnetic analyzers (i.e., when the magnetic field is changed in time), the FT-ICR technique detects all 

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