The invention relates to ion-guide systems for the transfer, cooling, fragmentation, selection and temporary storage of ions. The invention consists in embedding systems, made from one or more straight or curved rods to which a single or multiphase radio frequency voltage is applied, in an external enveloping dc potential. The combination of the ion-repelling radio-frequency pseudo field around the rods and the external dc voltage field represents a new category of ion-guide systems. With external dc voltage fields, whose strength or penetration into the interior of the rod system varies along the axis of the system, the ions can be collected or propelled along the axis of the system. Filling the system with collision or damping gas allows the ions to be fragmented and cooled without any losses and the phase space volumes of the ions to be greatly reduced.