An imbalanced radio frequency (RF) field creates a retarding barrier near
the exit aperture of a multipole ion guide, in combination with the
extracting DC field such that the barrier provides an m/z dependent cut
of ion sampling. Contrary to the prior art, the mass dependent sampling
provides a well-conditioned ion beam suitable for other mass
spectrometric devices. The mass selective sampling is suggested for
improving duty cycle of o-TOF MS, for injecting ions into a
multi-reflecting TOF MS in a zoom mode, for parallel MS-MS analysis in a
trap-TOF MS, as well as for moderate mass filtering in fragmentation
cells and ion reactors. With the aid of resonant excitation, the mass
selective ion sampling is suggested for mass analysis.