It is common for mass spectrometry instruments to have various regions operating at different pressures along the length of the instrument. For instance, the source region may be operated at relatively high or atmospheric pressure, whereas the analyser region may be operated under high vacuum conditions (i.e. very low pressures). Various regions, for instance regions used for transportation and/or manipulation of ions, may be provided between the source and analyser regions that are operated at intermediate pressures.
For example, WO 2013/171495 (MICROMASS) discloses a mass spectrometer in which ions generated at an ion source are passed in sequence through a first vacuum chamber via an ion transfer ion guide, into a second vacuum chamber containing a quadrupole mass filter, into a gas collision cell, into an ion mobility separation device and a second gas collision cell before finally arriving at the mass analyser, with each of these devices/regions being operated at various pressures. The operating pressure in each region is selected according to the purpose of that region.
Other instruments having multiple pressures along the length of the instrument are disclosed e.g. in US 2013/0175442 (AGILENT), WO 00/16375 (VG ELEMENTAL), JP 2012-043672 (SHIMADZU) and WO 2014/080493 (SHIMADZU).
In some cases background gas may be allowed to flow freely between the different pressure regions. This gas may be used to carry ions in the direction of gas flow. For example, this may be exploited in the first vacuum stages of a mass spectrometer. In these instances the gas composition in sequential regions may be very similar.
In other cases, gases may be controlled such that they are prevented from entering another region by an outflow of gas from that region. For example, where ion mobility separation (“IMS”) devices are operated in the first vacuum stages of a mass spectrometer, ingress of source gas into the ion mobility separation device is prevented by excess pressure/flow of the ion mobility separation buffer gas. In this case, the ion mobility separation gas enters the previous or upstream region. This may also be the case where a high pressure ion mobility separation device is situated downstream of a low pressure quadrupole region.
It will be appreciated that in each of these cases there is an intermixing of gases between adjacent regions.
It is desired to provide improved methods of coupling gas-filled regions.