Plasma is the liquid part of the blood in which the blood cells are suspended. Plasma makes up half of the blood volume. Blood plasma has primarily a transport role. It transports blood cells and hormones throughout the body.

Plasma is extracted from whole blood by centrifugation. During the centrifugation process, the blood cells end up at the bottom of the tube and the yellowish liquid that remains is the plasma. More than 90% of plasma is water. Other components of plasma are mineral solutes such as trace elements and ions, respiratory gases (O2 and CO2) and organic solutes such as plasma proteins.

Sodium citrate is an anticoagulant. The anticoagulant properties of citrate are expressed by citrate ions forming calcium citrate complexes with Са2+ ions, effectively disrupting the blood clotting mechanism.