Patent ID: 8242440

Claim:
An ion transfer capillary tube for transferring background gas and entrained ions from an ionization chamber at substantially atmospheric pressure to an evacuated chamber of a mass spectrometer system, the ion transfer capillary tube comprising an inlet end for receiving the background gas and entrained ions within the ionization chamber, an outlet end for delivering the background gas and entrained ions to the evacuated chamber, an interior bore for transferring the background gas and entrained ions from the inlet end to the outlet end, and a portion having a cylindrical outer surface of constant outer diameter that mates with an internal bore of an enclosing body such that the ion transfer capillary tube is slideably removable from the enclosing body and mass spectrometer system in the direction opposite to the direction of travel of the ions during operation of the system, wherein the improvement comprises: a portion of the interior bore adjacent to and at the outlet end having an inner diameter that is greater than an inner diameter of an adjoining portion of the interior bore.