INVESTIGATION OF GHOST PEAKS CAUSED BY NONLINEAR FIELDS IN THE ION-TRAP MASS-SPECTROMETER

Mass spectral 'ghost peaks' are generated with the ion trap by the sup erposition of higher order multipole fields which originate through de viations from the pure quadrupole field. In data acquisition, when the amplitude of the RF voltage is tamping though a non-linear resonance point (q) on the Mathieu stability diagram, some ions (m(o)) are ejec ted by the non-linear field rather than by the quadrupole field at q(z ) = 0.908 on the beta(z) = 1 boundary. The prematurely ejected ions wi ll be seen as a peak at m(1) = (q/0.908)m(o), which we have termed a 'ghost peak'.