A device for the selective fractionation of ultrafine particles, comprising through-flowable separating columns (3) fluidically connected in series by connecting lines (1), in each case at least two alternately operated inlets (6, 7) for an ultrafine particle suspension that is to be separated, and at least one additional mobile phase, at least two alternately operable outlets (9, 10) for in each case one discharge suspension of ultrafine particles, shut-off valves (15, 16, 17, 18) with in each case two switching positions, a blocking switching position and a throughflow switching position, at each inlet and outlet, and control means for simultaneous switching of the throughflow switching positions of the shut-off valves, wherein at least one magnetic field source (4) is provided for in each case a magnetic field in each separating column (3).
