A system for analyzing one or more ion species of a sample comprising, an ion source, a pre-filter assembly including: a differential mobility spectrometer filter for passing one or more ion species of the sample through a time-varying field in an analytical gap between a pair of planar filter electrodes (518, 520), an outlet for providing a flow of ions from the differential mobility spectrometer filter, and a first mass spectrometer for receiving at an inlet at least a portion of the flow of ions from the pre-filter assembly and analyzing one or more ion species, and wherein the differential mobility spectrometer filter is positioned immediately between said ion source and said first mass spectrometer and is substantially in-line with the inlet of the first mass spectrometer and wherein a longitudinal axis of the analytical gap is aligned with a longitudinal axis of the inlet of the first mass spectrometer, characterized in that a gas inlet is positioned between the differential mobility spectrometer filter and the first mass spectrometer and wherein all gas entering through the gas inlet enters the first mass spectrometer, the system also comprises a controller that is configured to activate the differential mobility spectrometer filter when pre-filtering is desired when the first mass spectrometer is analyzing the one or more ion species and deactivate the differential mobility spectrometer filter when pre-filtering is not desired when the first mass spectrometer is analyzing the one or more ion species, and in that a vacuum pump of the first mass spectrometer draws gas flow through the differential mobility spectrometer. a pre-filter assembly including: a differential mobility spectrometer filter for passing one or more ion species of the sample through a time-varying field in an analytical gap between a pair of planar filter electrodes (518, 520), an outlet for providing a flow of ions from the differential mobility spectrometer filter, and a first mass spectrometer for receiving at an inlet at least a portion of the flow of ions from the pre-filter assembly and analyzing one or more ion species, and wherein the differential mobility spectrometer filter is positioned immediately between said ion source and said first mass spectrometer and is substantially in-line with the inlet of the first mass spectrometer and wherein a longitudinal axis of the analytical gap is aligned with a longitudinal axis of the inlet of the first mass spectrometer, characterized in that a gas inlet is positioned between the differential mobility spectrometer filter and the first mass spectrometer and wherein all gas entering through the gas inlet enters the first mass spectrometer, the system also comprises a controller that is configured to activate the differential mobility spectrometer filter when pre-filtering is desired when the first mass spectrometer is analyzing the one or more ion species and deactivate the differential mobility spectrometer filter when pre-filtering is not desired when the first mass spectrometer is analyzing the one or more ion species, and in that a vacuum pump of the first mass spectrometer draws gas flow through the differential mobility spectrometer.