A desired ion is isolated in an ion trapping volume by applying an ion isolation signal to a plurality of ions in the ion trapping volume, including the desired ion to be retained in the ion trapping volume and an undesired ion to be ejected from the ion trapping volume. The ion isolation signal includes a plurality of signal components spanning a frequency range. The plurality of signal components includes a first component having a frequency near a secular frequency of the desired ion, and an adjacent component having a frequency adjacent to the frequency of the first component. The first component has an amplitude greater than the amplitude of the adjacent component.