Mass Analyser

A mass analyser, comprising:

• an electrical field generator, comprising a field generating electrode 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 electric field generator and the first and second detection electrodes are configured such that the amplitude of the output from the differential amplifier is within an allowed range at a transition time, the allowed range being such that the output from the differential amplifier can be used to detect image currents from ions injected to the mass analyser and wherein an initialisation time period is defined between the time at which the field generating electrode begins to provide the time-varying electric field and the transition time;
• and
• wherein the application of a time-varying voltage to the field generating electrode causes mechanical oscillations in at least one of:
• the field generating electrode;
• the first detection electrode;
• and the second detection electrode, and wherein the mass analyzer is configured such that the time constant of damping for the mechanical oscillations is not significantly greater than the duration of the initialisation time period.

A method of mass analysis, comprising:

• providing a time-varying voltage to an electrical field generator comprising at least one field generating electrode, so as to provide a time-varying electric field for injection of ions to be analysed, excitation of ions to be analysed or both;
• receiving at first and second detection electrodes, a respective voltage pickup due to the time-varying electric field;
• providing from each of the first and second detection electrodes a respective detection signal, based on a respective image current at the detection electrode;
• and
• generating a differential amplifier 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 voltage pickup received at the first detection electrode is substantially the same as the voltage pickup received at the second detection electrode.

A method of manufacturing a mass analyser, comprising:

• providing an electrical field generator, comprising at least one field generating electrode configured to receive a time-varying voltage in order to provide a time-varying electric field for injection of ions to be analysed, excitation of ions to be analysed or both, the electrical field generator comprising at least one field generating electrode without a spatially symmetrical counterpart;
• arranging first and second detection electrodes such that each will receive a respective voltage pickup due to the time-varying electric field and such that each provides a respective detection signal based on a respective image current at the detection electrode;
• arranging a differential amplifier 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;
• and
• configuring the electric field generator and the first and second detection electrodes 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.

A method of manufacturing a mass analyser, comprising:

• providing an electrical field generator, comprising at least one field generating electrode configured to receive a time-varying voltage in order to provide a time-varying electric field for injection of ions to be analysed, excitation of ions to be analysed or both;
• arranging first and second detection electrodes such that each will receive a respective voltage pickup due to the time-varying electric field and such that each provides a respective detection signal based on a respective image current at the detection electrode;
• arranging a differential amplifier 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;
• and
• configuring the electric field generator and the first and second detection electrodes such that the amplitude of the output from the differential amplifier is within an allowed range at a transition time, the allowed range being such that the output from the differential amplifier can be used to detect image currents from ions injected to the mass analyser, an initialisation time period being defined between the time at which the field generating electrode begins to provide the time-varying electric field and the transition time;
• wherein the application of a time-varying voltage to the field generating electrode causes mechanical oscillations in at least one of:
• the field generating electrode;
• the first detection electrode;
• and the second detection electrode;
• and
• the method further comprising adjusting the mass analyser such that the time constant of damping for the mechanical oscillations is not significantly greater than the duration of the initialisation time period.