A method is disclosed for generating a mass spectrum, e.g. for Fourier transform mass spectrometry, having improved resolving power. The method includes steps of acquiring a plurality of mass spectra from a mass spectrometer using image current detection determining the centroids of at least some of the peaks which have a sufficient signal-to-noise (S/N) ratio so that the variation of the centroid of each such peak from the plurality of mass spectra is significantly lower than the full-width at half-maximum, dM, of the peak in the m/z domain; and generating a histogram of the centroids determined from the plurality of acquired mass spectra thereby forming a composite mass spectrum. The resultant composite mass spectrum comprises peaks having full-width at half-maximum, dMC, significantly narrower than the peak width, dM, of the corresponding peaks in the plurality of acquired mass spectra.