Application of SIMION 6.0 to Filament Design for Mass Spectrometer Ionization Sources


ASMS, 1996

Steven Colby, Scientific Instrument Services

SIMION software has been used to model ion and electron optics for over 10 years. A new release, Version 6.0 for windows, has greatly expanded the versatility of the software. We report the use of this program to examine problems in the design of electron impact and chemical ionization sources for mas spectrometers. The design of the source is critical because of the need for sensitivity and the influence that variations in ionization have on the quantitative reproducibility of ion signal. The issues of concern include the region over which ionization occurs, the volume from which detected ions can be generated, and the loss of ions due to space change effects. Tolerances for the manufacture and positioning of the ion optics elements can be identified using SIMION calculations. These have shown a number of interesting results. For example, the optimum strength of the magnetic field within the source is different for electron impact and chemical ionization sources. Because of the graphic abilities of SIMION the results of our calculations can be clearly illustrated and we are able to demonstrate the consequences of design improvements.