A system for the analysis of polyionic molecules by mass spectrometry is provided. The polyionic molecule is attached to a charged tag which neutralizes some of the charge on the polyionic analyte. The formed adduct with a reduced net charge is then analyzed by mass spectrometry, and the determined molecular weight of the adduct can be used to calculate the molecular weight of the analyte. Mass spectrometric analyses of polynucleotides and proteins are particularly amenable to this method.