A two-dimensional radial-ejection ion trap is constructed from four apertured electrodes having inwardly facing hyperbolic surfaces, with each electrode being spaced from the centerline by a distance r that is greater than the hyperbolic radius r0 defined by the hyperbolic surfaces. This geometry produces a balanced symmetrical trapping field that has a negligible octopole field component and a relatively large dodecapole or icosapolar field component. In one specific implementation, the ion trap is selectably operable as a quadrupole mass filter by applying a filtering DC voltage to the electrodes.