Investigation of 'ghost' peaks caused by non-linear fields in the ion trap mass spectrometer

Mass spectral ‘ghost peaks’ are generated with the ion trap by the superposition of higher order multipole fields which originate through deviations from the pure quadrupole field. In data acquisition, when the amplitude of the RF voltage is ramping though a non‐linear resonance point (q*) on the Mathieu stability diagram, some ions (m0) are ejected by the non‐linear field rather than by the quadrupole field at qz=0.908 on the βz=1 boundary. The prematurely ejected ions will be seen as a peak at m1=(q*/0.908)m0, which we have termed a ‘ghost peak’.