Device for the selective fractionation of ultrafine particles, comprising a) at least three through-flowable separating columns, fluidically connected in series by connecting lines and in a predetermined flow direction, b) at least one feed into the connecting line, located upstream of each separating column, with in each case at least two alternately operated inlets (6, 7) for an ultrafine particle suspension that is to be separated, as well as at least one additional mobile phase, c) at least one discharge branching off from the connecting line, downstream of each separating column, with in each case two alternately operated outlets (9, 10), each one for a suspension of ultrafine particles, wherein the ultrafine particles of the first discharge suspension exhibit a more powerful reciprocal effect with the packing of the separating column than the ultrafine particles of a second discharge suspension, d) 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 e) control means for simultaneous switching of the throughflow positions of the shutoff valves of the inlets and of the outlets, wherein in each case at least one inlet and at least one outlet for the ultrafine particle suspension which is to be separated, of the at least one additional mobile phase and of the at least two discharge suspensions of ultrafine particles, can be switched to the throughflow position, wherein f) at least one separating column is arranged between the outlet switched to the throughflow position for the second discharge suspension of ultrafine particles and the inlet, upstream of this and switched to the throughflow position for the ultrafine particle suspension which is to be separated, g) at least one separating column is arranged between the outlet for the first discharge suspension of ultrafine particles, switched to the throughflow position, and the inlet downstream of this and switched to the throughflow position, for an ultrafine particle suspension which is to be separated, and h) at least one separating column is arranged between the outlet for the first discharge suspension of ultrafine particles, switched to the throughflow position, and the inlet upstream of this, switched to the throughflow position, for an additional mobile phase, characterised in that i) at least one magnetic field source is provided in each case for a magnetic field in each separating column. a) at least three through-flowable separating columns, fluidically connected in series by connecting lines and in a predetermined flow direction, b) at least one feed into the connecting line, located upstream of each separating column, with in each case at least two alternately operated inlets (6, 7) for an ultrafine particle suspension that is to be separated, as well as at least one additional mobile phase, c) at least one discharge branching off from the connecting line, downstream of each separating column, with in each case two alternately operated outlets (9, 10), each one for a suspension of ultrafine particles, wherein the ultrafine particles of the first discharge suspension exhibit a more powerful reciprocal effect with the packing of the separating column than the ultrafine particles of a second discharge suspension, d) 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 e) control means for simultaneous switching of the throughflow positions of the shutoff valves of the inlets and of the outlets, wherein in each case at least one inlet and at least one outlet for the ultrafine particle suspension which is to be separated, of the at least one additional mobile phase and of the at least two discharge suspensions of ultrafine particles, can be switched to the throughflow position, wherein f) at least one separating column is arranged between the outlet switched to the throughflow position for the second discharge suspension of ultrafine particles and the inlet, upstream of this and switched to the throughflow position for the ultrafine particle suspension which is to be separated, g) at least one separating column is arranged between the outlet for the first discharge suspension of ultrafine particles, switched to the throughflow position, and the inlet downstream of this and switched to the throughflow position, for an ultrafine particle suspension which is to be separated, and h) at least one separating column is arranged between the outlet for the first discharge suspension of ultrafine particles, switched to the throughflow position, and the inlet upstream of this, switched to the throughflow position, for an additional mobile phase, characterised in that i) at least one magnetic field source is provided in each case for a magnetic field in each separating column.