A method of carrying out mass spectrometry, comprising: using an electrostatic or electrodynamic ion trap to contain a plurality of ions, each ion having a mass to charge ratio, the ions having a first plurality of mass to charge ratios, each ion following a path within the electrostatic or electrodynamic ion trap having a radius; and for each of a second plurality of the mass to charge ratios: modulating the radii of the ions in a mass to charge ratio-dependent fashion dependent upon the mass to charge ratio; fragmenting the ions thus modulated in a radius-dependent fashion; and determining a mass spectrum of the ions.