Patent ID: 6239429
Filing Date: 2001-05-29
Classification: H01J

Abstract:
A quadrupole mass spectrometer sensor of self-aligning design comprising:a hot-filament, electron-impact ion source for generating ions of the ambient gas in which the sensor is placed;a quadrupole mass filter assembly for selecting ions of specific mass-to-charge ratios from among said ions, the assembly comprising a central axis, a plurality of equal, non-magnetic, conductive, cylindrical filter rods and an insulating retainer block, said retainer block being formed as an annular body having a plurality of axial, rod receiving grooves disposed on the inner surface thereof, the rods being engaged to the grooved inner surface for the sole support thereof, wherein said cylindrical insulating retainer block has a circular outer diameter that is substantially coaxial with the central axis, and has a symmetric inner surface that is substantially coaxial with the central axis, and has two end faces that are substantially perpendicular to the central axis;a detector for collecting the charge of said selected ions;a cylindrical entrance electrode having an entrance aperture that defines the area through which said ions enter said quadrupole mass filter from said ion source wherein said entrance electrode has a mounting face and lip formed thereon for receiving the retainer block and positioning the entrance electrode in axial alignment therewith; anda cylindrical exit electrode having an exit aperture that defines the area through which said selected ions exit said quadrupole mass filter to said detector wherein said exit electrode has a mounting face and a lip formed thereon, for receiving the retainer block and positioning the exit electrode in axial alignment therewith.