Patent ID: 8283626

Claim:
A mass spectrometer comprising: an Electron Transfer Dissociation or Proton Transfer Reaction device comprising an ion guide comprising a plurality of electrodes; and a control system arranged and adapted: (i) to determine the intensity or abundance I1 of one or more parent or precursor ions having a first charge state which emerge from said ion guide; (ii) to determine the intensity or abundance I2 of one or more ions which emerge from said ion guide and which correspond with parent or precursor ions which have been charge reduced and which have a second charge state, wherein said second charge state is lower than said first charge state; and (iii) to vary the velocity or amplitude of one or more transient DC voltages which are applied to said electrodes in order to maintain the ratio I1/I2 or I2/I1 at a substantially constant value R with time.