Patent ID: 8841604

Claim:
A mass analyser, comprising: an electrical field generator, configured to provide a time-varying electric field for injection of ions to be analysed, excitation of ions to be analysed or both; first and second detection electrodes, each of which is arranged such that it will receive a respective voltage pickup due to the time-varying electric field and so as to provide a respective detection signal based on a respective image current at the detection electrode; and a differential amplifier, arranged to provide an output based on the difference between the detection signal for the first detection electrode and the detection signal for the second detection electrode; wherein the electrical field generator comprises at least one field generating electrode without a spatially symmetrical counterpart; and wherein the electric field generator and the first and second detection electrodes are configured such that the capacitance between each field generating electrode and the first detection electrode is substantially the same as the capacitance between that field generating electrode and the second detection electrode.