A mass spectrometry method in which a supplemental AC voltage signal having at least one high power frequency component, and at least one low power frequency component, is applied to an ion trap. Each high power component has an amplitude sufficiently large to eject one or more selected ions from the trap, by resonantly exciting the ions. Each low power component has an amplitude sufficient to induce dissociation (or reaction) of one or more selected ions, but insufficient to resonate the ions for detection. The frequency (or band of frequencies) of each high and low power frequency component is selected to match a resonance frequency of ions having a desired mass-to-charge ratio. Each low power component is applied for the purpose of inducing dissociation or reaction of specific trapped ions, which may be parent, daughter, reagent, or product ions, and each high power component is applied to eject undesired products of each such dissociation or reaction process from the trap. In accordance with the invention, a supplemental voltage signal having appropriately selected high and low power frequency components is applied to a trap during an (MS).sup.n or CI, or combined CI/(MS).sup.n, mass spectrometry operation.