Simulation of a QMS Including the Effects of Pressure in the Electron-Impact Ion Source

This paper is concerned with the computer modeling of a quadrupole mass spectrometer (QMS) to include the effect of pressure in the ion source. The paper simulates the spectra over the pressure range from 10^-6 to 10^-4 mbar. An important contribution is the development of a novel procedure to include pressure dependence of the ion source to allow better prediction of instrument performance. Electron-impact total ionization cross sections in the ionic current expression are calculated using the binary-encounter-Bethe theory for argon gas. The predicted results show good agreement with the experimental results obtained from a commercial QMS used for residual gas analysis.