Influence of a Fringing Field on the Sensitivity of the Quadrupole Mass Spectrometer

Fringing fields arising from both ends of a quadrupole electrode are recognized to affect the performance of the quadrupole mass spectrometer (QMS). The fringes were defined as two gaps between an ion source and the quadrupole (inlet), and between a detector case and the quadrupole (outlet). In this paper, the influence of inlet and outlet fringe lengths on the sensitivity of the QMS was experimentally studied using the movable ion source and the quadrupole, both of which were mounted on a three-dimensional manipulator. 4He+ (mass 4), 40Ar2+ (20), 40Ar+ (40), 132Xe2+ (66) and 132Xe+ (132) peaks were monitored. Except for 4He+, all species showed maximum peak intensities at nf of 0.7-1.0 cycles when the inlet fringe length was expressed in an rf cycle nf. However, all the peak intensities decreased consistently with increasing outlet fringe lengths. The experimental results of the sensitivity corresponded qualitatively with the calculated ones.