Abstract: Quadrupole ion optical devices configured to arrange paths of each of a plurality of ion beams exiting from a mass analyser towards detector elements of a mass spectrometer. Example quadrupole ion optical device comprise 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, and electrical circuitry configured to supply at least a first set of voltages or a second set of voltages to the plurality of electrodes. The application of the second set of voltages generates a quadrupole potential having a saddle point at a position in a plane normal to the central axis that is displaced compared to a position in a plane normal to the central axis for a saddle point of a quadrupole potential generated upon application of the first set of voltages.