A method and apparatus of combining an ion volume, a lens stack, and an ion optic that similarly cooperates with a detached multipole ion guide is herein incorporated into a single sub-assembly that can be removed from a mass spectrometer instrument without venting. Such an arrangement allows an operator to clean all parts of the ion path that get contaminated in normal operation, reassemble and reinsert in a timely manner and then pump down to an acceptable vacuum without having to vent the system.