A method of mass spectrometry is disclosed wherein a signal output from an ion detector is digitized by an Analogue to Digital Converter and is then deconvoluted to determine one or more ion arrival times and one more ion arrival intensities. The process of deconvoluting the ion signal involves determining a point spread function characteristic of an ion arriving at and being detected by the ion detector. A distribution of ion arrival times which produces a best fit to the digitised signal is then determined given that each ion arrival is assumed to produce a response given by the point spread function. A plurality of ion arrival times are then combined to produce a composite ion arrival time-intensity spectrum.