Patent ID: 7119330

Claim:
A mass spectrometer including: a plasma ion source for providing analyte ions, a vacuum chamber, and a sampling and a skimmer interface arrangement between the plasma ion source and the vacuum chamber for admitting plasma which contains analyte ions into the vacuum chamber, electrode means in the vacuum chamber for extracting an ion beam containing analyte ions from the admitted plasma for transmission through an aperture in said electrode means to a mass analyser and ion detector contained in a further vacuum chamber, the electrode means including at least one electrode which is configured and associated with the skimmer such that a region of the vacuum chamber between the skimmer and said at least one electrode will have a relatively higher pressure than the pressure elsewhere in the vacuum chamber thereby to provide a collisional gas volume for attenuating polyatomic and multicharged interfering ions, wherein the skimmer has a conical interior surface and said at least one electrode is sealingly mounted on the conical interior surface of the skimmer and electrically insulated therefrom whereby said region of the vacuum chamber is a volume defined by the conical interior surface and the at least one electrode.