An improved ion funnel design is disclosed that decreases the axial RF
(parasite) fields at the ion funnel exit. This is achieved by addition of
one or more compensation electrodes after the conductance limit
electrode. Various RF voltage profiles may be applied to the various
electrodes minimizing the parasite axial potential wells. The smallest RF
aperture that serves as the conductance limiting electrode is further
reduced over standard designs. Overall, the ion funnel improves
transmission ranges of both low m/z and high m/z ions, reducing RF
activation of ions and decreasing the gas load to subsequent differential
pumping stages.