A device for field flux fractioning, comprising - a sensor for determining the presence of particles in a carrier liquid, - at least one essentially closed oblong channel (20; 50), which comprises a first end (20a; 50a) with a first connection (22; 52) and a second end (20b; 50b) with a second connection (24; 54) and its wall comprises at least one section extending in the longitudinal direction of the channel (20; 50), impermeable for the particles but permeable for the carrier liquid, - a pump, which comprises an inlet and an outlet and is provided to convey the carrier liquid, - a first liquid path, which connects the outlet of the pump to the first connection (22; 52) of the channel (20; 50), - a second liquid path, which connects the second connection (24; 54) of the channel (20; 54) to a first switching means, through which the second liquid path can be connected in a first switch position to the outlet of the pump and in a second switch position to the sensor, - an injection means, which is arranged in the first liquid path and provided to inject a sample comprising particles into the carrier liquid flowing through the first liquid path, and - a flow volume distribution means (8, 10, 12), which divides the flow volume conveyed by the pump in the first switch position of the first switching means at a predetermined distribution ratio to the first liquid path and the second liquid path and comprises a first flow volume control means, which is arranged in the first liquid path and is provided for the control of the flow volume of the carrier liquid in the first liquid path and comprises a first valve to adjust the flow volume of the carrier liquid in the first liquid path, wherein - the first flow volume control device comprises a first measuring means to measure the flow volume of the carrier liquid, - the valve is arranged upstream in reference to this first measuring means and is provided for controlling the flow volume of the carrier liquid in the first liquid path in consideration of the measurements of the first measuring means, and - the pump is provided to convey the carrier liquid in a defined constant flow volume. - a sensor for determining the presence of particles in a carrier liquid, - at least one essentially closed oblong channel (20; 50), which comprises a first end (20a; 50a) with a first connection (22; 52) and a second end (20b; 50b) with a second connection (24; 54) and its wall comprises at least one section extending in the longitudinal direction of the channel (20; 50), impermeable for the particles but permeable for the carrier liquid, - a pump, which comprises an inlet and an outlet and is provided to convey the carrier liquid, - a first liquid path, which connects the outlet of the pump to the first connection (22; 52) of the channel (20; 50), - a second liquid path, which connects the second connection (24; 54) of the channel (20; 54) to a first switching means, through which the second liquid path can be connected in a first switch position to the outlet of the pump and in a second switch position to the sensor, - an injection means, which is arranged in the first liquid path and provided to inject a sample comprising particles into the carrier liquid flowing through the first liquid path, and - a flow volume distribution means (8, 10, 12), which divides the flow volume conveyed by the pump in the first switch position of the first switching means at a predetermined distribution ratio to the first liquid path and the second liquid path and comprises a first flow volume control means, which is arranged in the first liquid path and is provided for the control of the flow volume of the carrier liquid in the first liquid path and comprises a first valve to adjust the flow volume of the carrier liquid in the first liquid path, - the first flow volume control device comprises a first measuring means to measure the flow volume of the carrier liquid, - the valve is arranged upstream in reference to this first measuring means and is provided for controlling the flow volume of the carrier liquid in the first liquid path in consideration of the measurements of the first measuring means, and - the pump is provided to convey the carrier liquid in a defined constant flow volume.