Predicted behaviour of QMF systems with and without prefilters using accurate 3D fields

Abstract

Computer simulation enables the effects of a much wider range of design parameters of quadrupole mass filters (QMFs) to be investigated than is economically possible by experiment. Large deviation from ideal behaviour arises from effects of the fringe field regions and is only predicted correctly if the three dimensional fringe fields are determined accurately.The boundary element method, BEM, was used to compute accurate 3D electric fields for complete QMF systems with and without prefilters. Detailed examination of system behaviour without prefilters was used to determine where the effects of fringe fields are particularly detrimental. Examination was extended to systems with prefilters to investigate the required prefilter length and the improvement in performance. The results confirmed that use of a prefilter improves performance in most situations; for high m/z the improvement was large. The results support the original claims of Brubaker although behaviour is more complicated than is described by Brubaker.The results are relevant to QMF designers and users and especially for miniature systems for portable mass spectrometry with the aim to optimise performance whilst maintaining a small instrument footprint.