Sodium triphosphate (STP), also sodium tripolyphosphate (STPP), or tripolyphosphate (TPP),
[http://www.mst.dk/English/ Danish Environmental Protection Agency], Accessed 2008-07-15) is an inorganic compound with formula Na₅P₃O₁₀. It is the sodium salt of the polyphosphate 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 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, 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 [O₃POP(O)₂OPO₃]⁵⁻. Many related di-, tri-, and polyphosphates are known including the cyclic triphosphate (e.g. sodium trimetaphosphate). It binds strongly to metal cations as both a bidentate and tridentate chelating agent.

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

Food

STPP is a preservative for seafood, meats, poultry, and compound feed, 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 lists STPP as Generally recognized as safe.

Other

Other uses (hundreds of thousands of tons/year) include ceramic engineering, ceramics (decrease the viscosity of glazes up to a certain limit), leather tanning (as masking agent and synthetic tanning agent - SYNTAN), anticaking agents, setting retarders, flame retardants, paper, anticorrosion compound, anticorrosion pigments, textiles, rubber manufacture, fermentation (biochemistry), fermentation, antifreeze." TPP is used as a polyanion crosslinker in polysaccharide based drug delivery. Toothpaste.

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 soluble, water-soluble, STPP is not significantly removed by waste water treatment. STPP hydrolyses to orthophosphate, phosphate, which is assimilated into the natural phosphorus cycle. Detergents containing phosphorus contribute to the eutrophication of many fresh waters. Potomac green water

References

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