Sodium triphosphate (STP), also sodium tripolyphosphate (STPP), or tripolyphosphate (TPP),
ttp://www.mst.dk/English/ Danish Environmental Protection Agency Accessed 2008-07-15) is an inorganic compound with formula Na₅P₃O₁₀. It is the

sodium Sodium is a chemical element with the symbol Na (from Latin ''natrium'') and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table. Its only stable ...

salt of the

polyphosphate Polyphosphates are salts or esters of polymeric oxyanions formed from tetrahedral PO4 (phosphate) structural units linked together by sharing oxygen atoms. Polyphosphates can adopt linear or a cyclic ring structures. In biology, the polyphosphate e ...

penta-anion, which is the conjugate base of triphosphoric acid. It is produced on a large scale as a component of many domestic and industrial products, especially detergents. Environmental problems associated with

eutrophication Eutrophication is the process by which an entire body of water, or parts of it, becomes progressively enriched with minerals and nutrients, particularly nitrogen and phosphorus. It has also been defined as "nutrient-induced increase in phytopla ...

are attributed to its widespread use.

Preparation and properties

Sodium tripolyphosphate is produced by heating a stoichiometric mixture of disodium phosphate, Na₂HPO₄, and

monosodium phosphate Monosodium phosphate (MSP), also known as monobasic sodium phosphate and sodium dihydrogen phosphate, is an inorganic compound of sodium with a dihydrogen phosphate (H2PO4−) anion. One of many sodium phosphates, it is a common industrial chemical ...

, NaH₂PO₄, under carefully controlled conditions. :2 Na₂HPO₄ + NaH₂PO₄ → Na₅P₃O₁₀ + 2 H₂O In this way, approximately 2 million tons are produced annually. STPP is a colourless salt, which exists both in anhydrous form and as the hexahydrate. The anion can be described as the pentanionic chain ₃POP(O)₂OPO₃sup>5−. Many related di-, tri-, and polyphosphates are known including the cyclic triphosphate (e.g.

sodium trimetaphosphate Sodium trimetaphosphate (also STMP), with formula Na3P3O9, is one of the metaphosphates of sodium. It has the formula but the hexahydrate is also well known. It is the sodium salt of trimetaphosphoric acid. It is a colourless solid that finds ...

). It binds strongly to metal cations as both a bidentate and tridentate

chelating agent Chelation is a type of bonding of ions and molecules to metal ions. It involves the formation or presence of two or more separate coordinate bonds between a polydentate (multiple bonded) ligand and a single central metal atom. These ligands ar ...

Uses

Detergents

The majority of STPP is consumed as a component of commercial detergents. It serves as a "builder", industrial jargon for a water softener. In hard water (water that contains high concentrations of Mg²⁺ and Ca²⁺), detergents are deactivated. Being a highly charged

, TPP⁵⁻ binds to dications tightly and prevents them from interfering with the sulfonate detergent.

Food

STPP is a

preservative A preservative is a substance or a chemical that is added to products such as food products, beverages, pharmaceutical drugs, paints, biological samples, cosmetics, wood, and many other products to prevent decomposition by microbial growth or by ...

for seafood, meats, poultry, and animal feeds. It is common in food production as E number E451. In foods, STPP is used as an emulsifier and to retain moisture. Many governments regulate the quantities allowed in foods, as it can substantially increase the sale weight of seafood in particular. The United States

Food and Drug Administration The United States Food and Drug Administration (FDA or US FDA) is a List of United States federal agencies, federal agency of the United States Department of Health and Human Services, Department of Health and Human Services. The FDA is respon ...

lists STPP as Generally recognized as safe.

Other

Other uses (hundreds of thousands of tons/year) include

ceramics A ceramic is any of the various hard, brittle, heat-resistant and corrosion-resistant materials made by shaping and then firing an inorganic, nonmetallic material, such as clay, at a high temperature. Common examples are earthenware, porcelain ...

(decrease the viscosity of glazes up to a certain limit),

leather tanning Tanning is the process of treating skins and hides of animals to produce leather. A tannery is the place where the skins are processed. Tanning hide into leather involves a process which permanently alters the protein structure of skin, makin ...

(as masking agent and synthetic tanning agent - SYNTAN), anticaking agents, setting retarders,

flame retardant The term flame retardants subsumes a diverse group of chemicals that are added to manufactured materials, such as plastics and textiles, and surface finishes and coatings. Flame retardants are activated by the presence of an ignition source and ...

paper Paper is a thin sheet material produced by mechanically or chemically processing cellulose fibres derived from wood, rags, grasses or other vegetable sources in water, draining the water through fine mesh leaving the fibre evenly distrib ...

, anticorrosion

pigments A pigment is a colored material that is completely or nearly insoluble in water. In contrast, dyes are typically soluble, at least at some stage in their use. Generally dyes are often organic compounds whereas pigments are often inorganic compoun ...

, textiles,

rubber Rubber, also called India rubber, latex, Amazonian rubber, ''caucho'', or ''caoutchouc'', as initially produced, consists of polymers of the organic compound isoprene, with minor impurities of other organic compounds. Thailand, Malaysia, an ...

manufacture, fermentation,

antifreeze An antifreeze is an additive which lowers the freezing point of a water-based liquid. An antifreeze mixture is used to achieve freezing-point depression for cold environments. Common antifreezes also increase the boiling point of the liquid, all ...

." TPP is used as a polyanion crosslinker in polysaccharide based

drug delivery Drug delivery refers to approaches, formulations, manufacturing techniques, storage systems, and technologies involved in transporting a pharmaceutical compound to its target site to achieve a desired therapeutic effect. Principles related to dr ...

Toothpaste Toothpaste is a paste or gel dentifrice used with a toothbrush to clean and maintain the aesthetics and health of teeth. Toothpaste is used to promote oral hygiene: it is an abrasive that aids in removing dental plaque and food from the teeth, ...

Health effects

High serum phosphate concentration has been identified as a predictor of cardiovascular events and mortality. Whilst phosphate is present in the body and food in organic forms, inorganic forms of phosphate such as sodium triphosphate are readily adsorbed and can result in elevated phosphate levels in serum. Salts of polyphosphate anions are moderately irritating to skin and mucous membranes because they are mildly alkaline.

Environmental effects

Because it is very

water-soluble In chemistry, solubility is the ability of a substance, the solute, to form a solution with another substance, the solvent. Insolubility is the opposite property, the inability of the solute to form such a solution. The extent of the solub ...

, STPP is not significantly removed by

waste water treatment Wastewater treatment is a process used to remove contaminants from wastewater and convert it into an effluent that can be returned to the water cycle. Once returned to the water cycle, the effluent creates an acceptable impact on the environme ...

. STPP hydrolyses to

phosphate In chemistry, a phosphate is an anion, salt, functional group or ester derived from a phosphoric acid. It most commonly means orthophosphate, a derivative of orthophosphoric acid . The phosphate or orthophosphate ion is derived from phosph ...

, which is assimilated into the natural

phosphorus cycle The phosphorus cycle is the biogeochemical cycle that describes the movement of phosphorus through the lithosphere, hydrosphere, and biosphere. Unlike many other biogeochemical cycles, the atmosphere does not play a significant role in the moveme ...

. Detergents containing phosphorus contribute to the

of many fresh waters. Potomac green water

References

{{Sodium compounds Food additives Sodium compounds Phosphates E-number additives