A method of mass spectrometry is disclosed wherein voltage signals from an ion detector are analysed. A second differential of each voltage signal is obtained and the start and end times of observed voltage peaks are determined. The intensity and average time of each voltage peak is then determined and the intensity and time values are stored. An intermediate composite mass spectrum is then formed by combining the intensity and time values which relate to each voltage peak observed from multiple experimental runs. The various pairs of time and intensity data are then integrated to produce a smooth continuum mass spectrum. The continuum mass spectrum may then be further processed by determining the second differential of the continuum mass spectrum. The start and end times of mass peaks observed in the continuum mass spectrum may be determined. The intensity and mass to charge ratio of each mass peak observed in the continuum mass spectrum may then determined. A final discrete mass spectrum comprising just of an intensity value and mass to charge ratio per species of ion may then be displayed or output.