The invention relates to devices and methods for the storage of ions in mass spectrometers. The invention proposes the generation and superposition of two multipole fields of different order, independent of each other, in an RF multipole rod system. In an embodiment with eight pole rods, for example, it is thus possible to jointly store low-energy electrons in a central RF quadrupole field, which effectively acts only on electrons and holds them together radially, on the one hand, and multiply charged heavy positive ions in an RF octopole field, which effectively acts only on the ions, on the other hand, in order to fragment the positive ions by electron capture dissociation (ECD). In a different embodiment, multiply charged positive analyte ions and suitable negative reactant ions can react with each other in an octopole field by electron transfer dissociation (ETD) with a high fragmentation yield, and the fragment ions can subsequently be bundled by a transition to a quadrupole field to form a fine ion beam, which can leave the multipole rod system axially. A mixture of hexapole and dodecapole systems is also possible.