The invention relates to a device (1) for applying an electric field to a suspension of cells, cell derivatives, organelles, sub-cellular particles and/or vesicles, comprising at least one chamber (6) which comprises at least two electrodes (4), and at least one separating element (13) which is movable within the chamber (6) between two terminal points (14, 15) and, if it is in a position between the terminal points (14, 15), separates at least one first compartment (26) of the chamber (6) from at least one second compartment (27) of the chamber (6). According to the invention each compartment (26, 27) is designed to hold the suspension and comprises at least one port (7, 8, 10, 11) for charging or discharging the suspension, so as to discharge an aliquot of the suspension from the chamber (6) and at the same time charge a further aliquot of the suspension into the chamber (6), wherein the separating element (13) is moved in a second direction opposite to a first direction, and wherein the separating element (13) separates the aliquots from each other.