Quadrupole ion optical device

A quadrupole ion optical device, for arrangement in a path of each of a plurality of ion beams exiting from a mass analyser towards a plurality of detector elements of a mass spectrometer, the plurality of ion beams being laterally separated at an exit from the mass analyser, the separation between the plurality of ion beams being proportional to the massto-charge ratio of ions in each of the plurality of ion beams, the quadrupole ion optical device comprising:

• a plurality of electrodes, arranged around a central axis and configured to generate a quadrupole potential through which the path of each of the plurality of ion beams can be passed, an application of voltages to the plurality of electrodes generating a quadrupole potential in a region bounded by the plurality of electrodes;
• and
• electrical circuitry configured to supply at least a first set of voltages or a second set of voltages to the plurality of electrodes, each voltage of the first or second set of voltages to be applied to one or more electrodes of the plurality of electrodes;
• wherein application of the first set of voltages generates a first quadrupole potential having a saddle point at a first position in a plane normal to the central axis that optimises an alignment of a first group of ion beams of interest, which are included in the plurality of ion beams, into a first respective set of detector elements of the plurality of detector elements by minimising an angle of incidence between each of the ion beams of interest of the first group and a direction normal to a detection surface of the respective detector element of the first set of detector elements at which the ion beam is received;
• wherein application of the second set of voltages generates a second quadrupole potential having a saddle point at a second position, different from the first position, in the plane normal to the central axis that optimises an alignment of a second group of ion beams of interest, which are included in the plurality of ion beams, into a second respective set of detector elements of the plurality of detector elements by minimising an angle of incidence between each of the ion beams of interest of the second group and a direction normal to a detection surface of the respective detector element of the second set of detector elements at which the ion beam is received;
• wherein the first and second groups of ion beams of interest differ in mass-to-charge ratio and the first and second respective sets of detector elements are oriented at different angles;
• wherein the quadrupole ion optical device is configured to provide a continuous flow of the plurality of ion beams from the mass analyser to the plurality of detector elements, without trapping ions within the quadrupole ion optical device.