Field flow fractionation apparatus

A field flow fractionation apparatus comprising:

• a detector for detecting fine particles,
• a separation channel comprising an inlet port and an outlet port at both ends, wherein the separation channel forms a space through which a carrier fluid flows between the inlet port and the outlet port, and the outlet port leads to the detector;
• a separation membrane which is a wall surface that defines the separation channel and is parallel to a channel flow in which a carrier fluid flows in the separation channel from the inlet port toward the outlet port, and has a property of permeating the carrier fluid and not permeating particles to be separated;
• and
• a discharge port that discharges the carrier fluid having permeated through the separation membrane to outside, wherein
• at least a part of the surface of the separation membrane is adapted with at least one ion exchange functional group.