A method of mass spectrometry is disclosed comprising: a) separating first ions or components of an analyte sample according to a physicochemical property other than ion mobility; b) separating said first ions or second ions formed from said components according to ion mobility; c) detecting the intensities of said first ions, or detecting the intensities of second ions formed from said components, or detecting the intensities of ions derived from said first or second ions; wherein the intensity of the ions detected at any given time is recorded together with an associated value of said physicochemical property and an associated value of said ion mobility so as to obtain spectral data; d) examining the intensities of the spectral data as a function of said ion mobility so as to detect an intensity peak in said spectral data, determining a discrete value of ion mobility for said peak, and defining a window of values of ion mobility that encompasses said discrete value; and e) filtering said spectral data so as to include only spectral data that has been associated with values of ion mobility that are within said window of ion mobility values.