Quadrupole mass filters with bent or bowed rod sets

Abstract The acceptance of ions by quadrupole mass filters with small longitudinal distortions is calculated. The rod sets are assumed to be bowed out or bent in at the centre. It is shown that quite small geometrical deviations (δ r 0 / r 0 ∼ 10 −3 ) can have significant effects for slow-moving ions under high-resolution conditions. Bowed rod sets tend to produce mass peaks with shoulders or satellites on the high-mass side and those bent inwards give structures on the low-mass side. The predicted characteristics are qualitatively similar to those frequently observed experimentally as performance is pushed to high levels.