Introduction

Trisodium citrate dihydrate is the dihydrate of trisodium citrate. It is produced by the complete neutralisation of citric acid with high-purity sodium hydroxide or carbonate and subsequent crystallisation. Trisodium citrate dihydrate (SC) or trisodium 2-hydroxy-propane-1,2,3-tricarboxylate is a sodium salt of citric acid. SC has a saline, mildly tart flavour. Trisodium citrate dihydrate occurs as white, granular crystals or as a white, crystalline powder with a pleasant, salty taste. It is slightly deliquescent in moist air, freely soluble in water and practically insoluble in ethanol (96 %).

Trisodium citrate dihydrate is a non-toxic, neutral salt with low reactivity. It is chemically stable if stored at ambient temperatures. Trisodium citrate dihydrate is fully biodegradable and can be disposed of with regular waste or sewage.

Structure

SC crystallizes as monoclinic dihydrate with space group C2/c, including eight molecules in the unit cell.

It contains one citrate anion, whose geometry is unexceptional, and three Na+ ions in the asymmetric unit. The Na+ ions are coordinated by citrate ions and water molecules, yielding a coordination number of 6, with rather irregular coordination polyhedra. Each citrate ion coordinates to nine Na+ ions as a bridging ligand, yielding a complex three-dimensional network. Additionally, the water ligands form hydrogen bonds to some of the carboxyl O atoms[1].

Uses

It is used mainly in foods as a food additive, for flavour or as a preservative in beverages, and in various technical applications mainly as buffering, sequestering or emulsifying agent. It is also used in blood collection tubes and to preserve blood in blood banks because citrate ions cheat calcium ions in the blood and disrupt blood clotting[2].

Researchers report the first preparation of single crystal Co(H2O)2Ni(CN)4￠4H2O via a sophisticated the combination method of the above traditional slow diffusion method using trisodium citrate dihydrate. The SC can serve as a chelating agent to control the nucleation rate and the crystal growth.

[1] Andreas Fischer, Giuseppe Palladino. “Trisodium citrate dihydrate.” Acta crystallographica. Section E, Structure reports online 59 11 (2004): m1080–m1082.

[2] H Tuner, M Korkmaz. “Effects of gamma radiation on solid trisodium citrate dihydrate: radical kinetics, radiosensitivity and dosimetry.” Radiation and Environmental Biophysics 49 4 (2010): 723–9.