Eliminating false harmonic signals from frequency spectra

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, which is generally paraboloidal in shape. Analysis of the oscillation frequencies of these ion clouds, preferably by means of a Fourier analysis, leads via a frequency spectrum to a mass spectrum. The invention consists in identifying false signals in the frequency spectrum as harmonics of a fundamental oscillation of a sample ion, and eliminating them where necessary. This may be achieved by analyzing each frequency peak and establishing whether it is a precise integer fraction or multiple of any other oscillation signal in the frequency domain data, and by comparing the signal height ratios of the spectrum with an instrument-specific spectrum of the harmonics for the mass spectrometer being used.