An ion-ion reaction cell is provided comprising a plurality of electrodes forming an ion guide. A transient DC voltage wave is applied to the electrodes in order to load reagent anions into the ion guide. Analyte cations are then subsequently transmitted through the ion-ion reaction cell by a subsequent transient DC voltage wave. Ion are arranged to undergo ion-ion reactions within the reaction cell and the resulting fragment ions which are formed within the reaction cell are then subsequently translated out of the reaction cell by means of a transient DC voltage wave.