Patent ID: 8119984

Claim:
A reagent ion source for a mass spectrometer, comprising: a reagent vapor source for supplying reagent vapor to a reagent ionization volume; the reagent ionization volume being located within a chamber of the mass spectrometer and having, during operation of the mass spectrometer, an interior region maintained at a low vacuum pressure; a set of electrodes disposed within the reagent ionization volume; a voltage source for controllably applying a discharge potential across the set of electrodes to generate an electrical discharge that ionizes the reagent vapor to produce reagent ions; a reagent ion outlet extending from the interior region of the reagent ionization volume to the chamber of the mass spectrometer; and at least one ion optical element for transporting the reagent ions to a succeeding chamber of the mass spectrometer, the at least one ion optical element being positioned along an analyte ion path; wherein the reagent ionization volume includes a discharge region extending between the set of electrodes, an ionization region communicating with the reagent ion outlet, and a partition dividing the discharge region from the ionization region, the partition having a conductance limited aperture formed therein such that the ionization region and the discharge region are held at substantially different pressures during device operation.