A Method of Computing Accurate 3D Fields of a Quadrupole Mass Filter and Their Use for Prediction of Filter Behavior

A method is described that enables the three-dimensional fields of a simple quadrupole mass filter (QMF) to be determined to a high accuracy. The technique produces accurate field values in the fringe field region as well as in the center of the filter. Using fields obtained typical filter performance is determined and shown to differ from that predicted when fringe fields are ignored. The computed performance shows features obtained experimentally and displays more complex variation with ion mass and other parameters than when fringe fields are ignored.