Sodium citrate dihydrate is a salt produced through the reaction of sodium carbonate with citric acid that serves as an anticoagulant for fractionated blood or plasma or for blood intended to be stored. Since 1914, this sodium salt has been used to preserve blood in blood banks. The calcium ions present in the blood are chelated by the citrate ion of sodium citrate. Chelation is a process in which organic compounds form multiple bonds with a single metal ion, resulting in the formation of complex molecules that are highly soluble, thus making the ions inactive so they won't react with other elements or ions to produce precipitates or coagulated fluid. Chelation of the calcium ions by the citrate ions results in the formation of calcium citrate complexes that consequently disrupt the natural tendency of the blood to clot.