The invention relates to mass spectrometers in which ion clouds are stored in two spatial directions by radial forces while oscillating largely harmonically at a mass-specific frequency in a third spatial direction perpendicular to the other two, in a potential minimum, the shape of which is as close to a parabola as possible. Analysis of the oscillation frequencies of these ion clouds, preferably by a Fourier analysis, leads via a frequency spectrum to a mass spectrum. The frequency spectrum is analyzed to identify false signals in the frequency spectrum as harmonics and eliminating them where necessary.