Some Causes of Poor Peak Shapes in Quadrupole Field Mass Analyzers

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Abstract
The performance of quadrupole field mass analyzers can be degraded by imperfections in the field. The imperfections may be the result of geometrical errors in the electrode structure or time errors in the applied waveforms. von Busch and Paul considered the nonlinear resonances resulting from these errors for the quadrupole mass filter using an analytical treatment of the ion motion. The authors extended this work to the three-dimensional quadrupole mass spectrometer, and using numerical computation of ion trajectories calculated the extent as well as the position of the resonances. In this paper, new experimental data are presented showing the occurrence of nonlinear resonances and the agreement between theory and experiment. The effect of adjustments in electrodes spacing on peak shapes was investigated. The results demonstrate that an analysis of the nonlinear resonances can provide an indication of the errors that are present. A new type of instability was found in the three-dimensional quadrupole, and a tentative explanation is presented.

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