EDTA,Sodium Fluroide,Sodium Heparin, Lithium Heparin, Potassium Oxalate. All I understand is that they prevent the clotting of blood.
Blood clotting is actually a very complicated process.
If you think about it, you don't want blood clots to form unless you really need them, so there are many steps which must be completed. When you first get an injury, the cells lining the capillaries are damaged and they release a chemical which attracts platelets to the area. The platelets are cells which stick together and form a temporary plug until a clot can be made. Then platelets release a factor which starts the clotting process on its way. Each step must happen in the right order for a clot to be finally formed.