DETAILED STUDY OF QUADRUPOLE MASS FILTER OPERATING WITH NO DC COMPONENT ON RODS

A report is given of the results of an extensive series of measurements of the quadrupole mass spectrometer performance when operating in the retarding mode. It is shown that this mode has some significant advantages over conventional operation for the mass range 40-500 a.m.u. In particular, there is less dependence upon mechanical imperfections in the quadrupole lens assembly, with consequent improvement in long term stability. Also, because the analyser operates without any applied d.c. voltage, the defocussing action at its entrance is reduced and therefore mass discrimination reduced. Satellite peaks have been identified as arising from third- and fourth-order disturbances in the quadrupole field. Mapping the position of these satellites over the whole stability region helps the understanding of the effect of field imperfections. © 1978.