An ion molecule reactor for generating analyte ions from analytes comprises: a) a reaction volume in which reagent ions can interact with the analytes in order to form analyte ions; b) at least one analyte inlet for introducing the analytes along an inlet path into the reaction volume whereby the inlet path runs essentially along at least a first section of the predefined transit path in the reaction volume; c) at least one reagent ion source and/or at least one reagent ion inlet for providing reagent ions into the reaction volume; d) at least one ion guide comprising an electrode arrangement which is configured for producing an alternating electrical, magnetic and/or electromagnetic field, that allows for guiding the reagent ions and/or the analyte ions at least along a section of the predefined transit path, preferably along the whole transit path, through the reaction volume.