Quadrupole mass spectrometer assembly

Abstract

A small, high performance quadrupole mass analyzer (QMA) that is simple to manufacture and assemble with high precision due to the design of key components using high precision circular geometries that are easily machined. The QMA has a single, cylindrical insulating retainer block, which supports at the four filter rods at their mid-points and precisely positions them in the conventional quadrupole configuration. The rods are held in the retainer block by radial fasteners that extend in radially from the outer diameter of the retainer block. These fasteners also constitute the electrical connection for each rod. The retainer block has precise outer diameter for alignment with the entrance and exit electrodes, each of which has a lip of matching precise inner diameter that fits over the outer diameter of the retainer block, thereby achieving virtually perfect coaxial alignment of these parts with one another. The entrance and exit electrodes each have a central aperture through which ions are focused along the central axis of the QMA. The precise coaxial alignment of the entrance and exit electrodes assures concentric positioning of their respective apertures with the central axis. The detector for collecting selected ions from the mass filter is positioned within, and shielded by, a cylindrical extension of the exit aperture. The QMA includes a hot filament ion source with special filaments mounted on a plate of special shape that fits into the end of the electron repeller cylinder thereby ensuring that a critically small gap between the filament supports and the electron repeller is not bridged.