Design of a Small Magnetic-Sector Mass Spectrometer with Reduced Mass Discrimination

Abstract

The design of a small, low-weight, single-focusing, magnetic sector mass spectrometer is reported with radius of curvature rm=5 cm, angle of magnetic sector φm=90°, intended for fast voltage scanning. The properties of this 90° instrument are compared to those of 60° and 180° instruments. The ion source of this spectrometer is the outcome of studies on ion extraction and transmission. It compares favorably with a conventional electron impact source as regards mass discrimination when voltage scanning is used. The choice of 90° for the magnetic sector has enabled us to use a multiplier for ion detection without being compelled to reduce the influence of the magnetic field as required in 180° instruments. A resolution (10% valley) of 50 at mass 40, at a minimum detectable pressure of 4×10−14 Torr=5.3×10−12 Pa using a single channel multiplier has been obtained.