A method of mass spectrometry is disclosed comprising providing a mixture of different analyte ions and supplying electrons or reagent ions to said mixture so as to transfer charge to the analyte ions. The transfer of charge causes at least some of the analyte ions to dissociate and others of the analyte ions not to dissociate, but to form intermediate ions of altered charge state. These intermediate ions are then isolated from other ions and excited so as to dissociate into daughter ions. The intermediate ions and their daughter ions are analyzed and associated with each other so that the intermediate can be identified from their daughter ions. The analyte ions can then be identified from the intermediate ions, since they differ only in charge state. The disclosed method enables analyte ions to be associated with their fragment ions, and therefore identified, without having to isolate individual analyte ions prior to their interactions with the electrons or reagent ions.