A blood collection device includes a tube for receiving a sample of whole blood for centrifugal separation into the lighter phase, plasma or serum, and the heavier cellular phase. The tube has a needle-pierceable stopper at one end for maintaining a negative pressure in the tube. A blood phase partitioning...http://www.google.ca/patents/US4055501?utm_source=gb-gplus-sharePatent US4055501 - Fluid collection device with phase partitioning means
