A high-frequency @[email protected] in which the @[email protected] motion of ions, having different mass/charge ratios, in a constant magnetic field is excited essentially simultaneously and coherently by a pulse or a radio-frequency electric field applied perpendicular to the magnetic field. The excited @[email protected] motion of the ions is subsequently detected on so-called receiver plates as a time domain signal that contains all the @[email protected] frequencies that have been excited. Fourier @[email protected] of the time domain signal results in the frequency domain FT-ICR signal which, on the basis of the inverse proportionality between frequency and the mass/charge ratio, can be converted into a @[email protected] The term is sometimes contracted to Fourier transform @[email protected] (FT-MS).