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Prediction of the effects of imperfect construction of a QMS filter
Author(s) -
Taylor Stephen,
Gibson John R.
Publication year - 2008
Publication title -
journal of mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.475
H-Index - 121
eISSN - 1096-9888
pISSN - 1076-5174
DOI - 10.1002/jms.1356
Subject(s) - chemistry , spurious relationship , displacement (psychology) , filter (signal processing) , position (finance) , voltage , filter paper , mechanics , chromatography , statistics , physics , psychology , mathematics , finance , quantum mechanics , computer science , computer vision , economics , psychotherapist
Modelling techniques have previously predicted the observed behaviour of perfectly manufactured QMS mass filters. These methods are extended to examination of the behaviour of imperfect QMS filters; this examination considers the behaviour of QMS filters with one rod displaced radially inward as this is a simple manufacturing defect that arises when a rod does not fit correctly into the mounting. The results demonstrate the well known, but poorly documented property, that exchanging the connections of a poorly performing QMS device sometimes improves performance. This is shown to arise because only a displacement of a y ‐rod produces a large effect. The results also show that displacement of a y ‐rod may produce a spurious additional peak known as a precursor. More detailed investigation suggests that precursors are not separate peaks but are formed because a section of the main peak is removed causing an apparent double peak. Finally results confirm that adjustment of the voltage applied to a displaced rod can be used to significantly improve the QMS behaviour. A small change by a fraction α in the position of a single rod may be compensated by a change of 2 × α in the voltage applied to that rod. Copyright © 2007 John Wiley & Sons, Ltd.