تری سدیم فسفات — trisodium phosphate, commonly abbreviated as TSP — is an inorganic compound with the chemical formula Na3PO4. It is a sodium salt of phosphoric acid in which all three replaceable hydrogen atoms have been substituted by sodium ions, making it a strongly alkaline compound when dissolved in water. Commercially available as a white, crystalline solid in both anhydrous and hydrated forms, trisodium phosphate is produced by the neutralization of phosphoric acid with sodium hydroxide or sodium carbonate. Its strong alkalinity, emulsifying properties, and cleaning effectiveness make it an important industrial chemical despite increasing regulatory scrutiny in some jurisdictions.

Trisodium phosphate dissolves in water to produce a strongly alkaline solution with a pH typically in the range of 11 to 12 for common use concentrations. This high alkalinity is central to its effectiveness as a cleaning and degreasing agent. The compound is moderately soluble in cold water, with solubility increasing with temperature. TSP is stable under normal storage conditions but should be kept dry to prevent caking and potential deactivation of the anhydrous form. Its reaction with carbon dioxide from air can gradually convert surface portions to sodium bicarbonate, which is minimized by proper sealed storage.

Trisodium phosphate is one of the most effective industrial degreasers and heavy-duty cleaning agents available. Its strongly alkaline solution saponifies — chemically converts to soluble soap — animal and vegetable fats and oils, while its emulsifying properties help disperse petroleum-based greases and oils that are not amenable to saponification. Industrial cleaning operations in food processing, manufacturing, and maintenance use TSP solutions to remove heavy soil deposits from equipment, floors, and structural surfaces. Its effectiveness against organic soils and its relatively low toxicity compared to solvent-based degreasers make it a preferred cleaning agent in many food processing facilities.

Trisodium phosphate is widely used in surface preparation before painting and coating operations. TSP solutions clean, degrease, and etch the surface simultaneously — the alkaline cleaning removes contaminants while a slight chemical etching of the surface improves the mechanical adhesion of subsequent coatings. Painters and contractors use TSP to prepare interior walls, wood surfaces, and metal substrates before applying primers and finish coatings. The surface after TSP treatment should be thoroughly rinsed with water and allowed to dry completely before painting begins.

Food-grade trisodium phosphate is approved as a food additive in many jurisdictions where it serves as a pH control agent, an emulsifier, and a sequestrant in processed foods. It is used in processed cheese products where it functions as an emulsifying salt that prevents the separation of fat during processing and storage. In poultry processing, TSP solutions are used as an antimicrobial rinse that reduces contamination on poultry carcasses. Pharmaceutical applications include use as a buffering agent and as a component of cleaning formulations for pharmaceutical manufacturing equipment.

Water treatment utilities use trisodium phosphate in boiler water treatment programs where it precipitates magnesium and calcium hardness ions as their insoluble phosphate salts, preventing the formation of adherent scale deposits on boiler tube surfaces. Phosphate treatment of boiler feedwater maintains the tube metal surfaces in a clean condition that preserves heat transfer efficiency and prevents the under-deposit corrosion that scale buildup can cause.

The use of phosphate compounds including trisodium phosphate has attracted regulatory attention in many jurisdictions because of phosphorus's role as a eutrophication nutrient in surface water bodies. The discharge of phosphate-containing cleaning product effluents to waterways can promote excessive algal growth that disrupts aquatic ecosystems. Many jurisdictions have restricted or prohibited the use of phosphate-containing cleaning products or set effluent limits on phosphate discharges. Industrial users should be aware of applicable regulations governing phosphate use and discharge in their jurisdiction.