Abstract: A separator has a generally cylindrical body and a water swellable material fitted around at least a portion of the generally cylindrical body or on the surface of a passage through the body. Upon being exposed to water the water swellable material swells to form a seal in the passage or within the tube or other vessel containing the separator. The separator is preferably used in a blood collection tube and has a specific gravity between specific gravities of a light phase and a heavy phase of the blood. After the blood has been collected and centrifuged the separator moves to a position between the light phase and the heavy phase and the water swellable material is exposed to water in the blood causing the material to swell and create a seal. Thereafter, the serum or plasma as well as white blood cells, lymphocytes, monocytes and platelets can be removed from the blood collection tube.

Abstract: A self-sealing fluid collection tube is provided with an elongated bore and a fluid entry end. A plug of super-absorbent material is provided within the tube opposite the fluid entry end. This plug is preferably vented and is adapted to seal the tube by expanding when contacted by a fluid, such as blood. After the fluid has been collected, the tube is placed in a pipetter-dispenser in which a plunger, which is inserted into the tube, moves through a calibrated distance thereby advancing the plug into the tube and expelling a selected volume of fluid from the tube. Alternatively, the fluid may be transferred into another receptacle by piercing the sealed plug to form a new vent channel to permit drainage of the collected fluid into a receptacle.