Disclosed herein is a mass spectrometry method having steps of: transmitting ions from an ion source through a mass filter; processing ions received from the mass filter in a discontinuous ion optical device downstream of the mass filter; operating the mass filter for a plurality of periods in a mass/charge ratio (m/z) filtering mode to transmit ions in one or more selected ranges of m/z to the discontinuous ion optical device; and operating the mass filter in a broad mass range mode transmitting ions of a mass range substantially wider than any mass range transmitted in the m/z filtering mode during one or more periods in which the discontinuous ion optical device is not processing ions from the mass filter. Utilization of this method assists to reduce contamination in the mass filter.