A method of assessing mass spectral peaks obtained by a mass spectrometer is disclosed. The method comprises: providing mass spectral data; selecting a chemical compound thought to have been analysed to provide said experimentally observed data, and modelling the spectral data predicted to be detected if the compound was to be mass analysed. Modelling comprises: generating a first set of spectral data including at least one mass peak that is predicted to be detected for the selected compound; generating a second set of spectral data by duplicating at least part of the first set of spectral data and shifting at least one mass peak in mass to charge ratio relative to the corresponding at least one mass peak in the first set of spectral data; and summing the amplitudes of the first and second sets of spectral data to produce a model data set having at least one mass peak.