An ion analysis apparatus comprising: an ionization source for generating ions from a sample; and an ion detector; wherein in use ions travel along an ion optical axis from the ionization source to the ion detector, the apparatus further comprising: a vacuum enclosure including a first vacuum region containing differential ion mobility means; and a second vacuum region containing a mass analyzer; pumping means configured to provide a pressure in the second vacuum region that is lower than the pressure in the first vacuum region; an ion inlet connecting the ionization source to the first vacuum region, wherein the first vacuum region is located before the second vacuum region on the ion optical axis such that in use ions generated from the sample undergo differential ion mobility analysis before mass analysis; and wherein in use the first vacuum region including the differential ion mobility means is at a pressure in the range 2kPa to 40kPa and the differential ion mobility means is driven by an asymmetric waveform having a frequency in the range 20kHz to 25MHz; and wherein the apparatus includes gas flow means for establishing a flow of gas into the first vacuum region so as to provide a gas medium for the differential ion mobility means. an ionization source for generating ions from a sample; and an ion detector; wherein in use ions travel along an ion optical axis from the ionization source to the ion detector, the apparatus further comprising: a vacuum enclosure including a first vacuum region containing differential ion mobility means; and a second vacuum region containing a mass analyzer; pumping means configured to provide a pressure in the second vacuum region that is lower than the pressure in the first vacuum region; an ion inlet connecting the ionization source to the first vacuum region, wherein the first vacuum region is located before the second vacuum region on the ion optical axis such that in use ions generated from the sample undergo differential ion mobility analysis before mass analysis; and wherein in use the first vacuum region including the differential ion mobility means is at a pressure in the range 2kPa to 40kPa and the differential ion mobility means is driven by an asymmetric waveform having a frequency in the range 20kHz to 25MHz; and wherein the apparatus includes gas flow means for establishing a flow of gas into the first vacuum region so as to provide a gas medium for the differential ion mobility means. a vacuum enclosure including a first vacuum region containing differential ion mobility means; and a second vacuum region containing a mass analyzer; a first vacuum region containing differential ion mobility means; and a second vacuum region containing a mass analyzer; pumping means configured to provide a pressure in the second vacuum region that is lower than the pressure in the first vacuum region; an ion inlet connecting the ionization source to the first vacuum region, wherein the first vacuum region is located before the second vacuum region on the ion optical axis such that in use ions generated from the sample undergo differential ion mobility analysis before mass analysis; and wherein in use the first vacuum region including the differential ion mobility means is at a pressure in the range 2kPa to 40kPa and the differential ion mobility means is driven by an asymmetric waveform having a frequency in the range 20kHz to 25MHz; and wherein the apparatus includes gas flow means for establishing a flow of gas into the first vacuum region so as to provide a gas medium for the differential ion mobility means.