A method for the cell separation from blood or from blood products, having the following steps: (i) inserting a blood bag (35) containing a blood product into a blood bag section (5) of a cartridge (1) (ii) inserting a tube (36) connected to the blood bag (35) into a product transport path (36) which connects the blood bag (35) to a product bag (33) wherein a first sensor (25) and a second sensor (85) are positioned along the product transport path (36), (iii) inserting the cartridge (1) into a rotor of a centrifuge, (iv) spinning the centrifuge for separating the individual blood components, (v) transporting a predetermined quantity of a blood component along the product transport path (36) at a first flow speed, (vi) detecting the composition of the transported blood component by the first sensor (25). The second sensor (85) also detects the composition of the transported blood component after the first sensor (25) has output a signal corresponding to a predetermined composition of the blood component. The transporting and the spinning are terminated when the second sensor (85) detects the predetermined composition and outputs a respective end signal, or when a predetermined period of time has elapsed.