Sodium Tripolyphosphate: An Essential Sequestrant and Builder

CAS Registry Number: 7758-29-4

Overview

Sodium tripolyphosphate (STPP), also known as pentasodium triphosphate or sodium triphosphate, is an inorganic polyphosphate salt with the chemical formula Na₅P₃O₁₀ and a molecular weight of 367.86 g/mol . It appears as a white powder or granular solid, readily soluble in water (approximately 20 g/100 mL at 25°C) with a mildly alkaline pH (9.0-10.0 for a 1% solution) . STPP is slightly hygroscopic and is stable under normal conditions, though incompatible with strong oxidizing agents and strong acids .

Key Applications

Detergents and Cleaning Products

STPP is most widely recognized as an indispensable builder in synthetic detergents, typically comprising 10-50% of the formulation . Its primary functions include:

• Metal Ion Sequestration: STPP effectively chelates hard water ions such as Ca²⁺ and Mg²⁺, preventing them from interfering with surfactant performance .

• Soil Suspension and Emulsification: It helps disperse and emulsify oily and particulate soils, keeping them suspended in the wash water .

• pH Buffering: STPP maintains the wash solution at an optimal alkaline pH (around 9.4) for effective cleaning .

• Anti-Caking: In powdered detergents, STPP absorbs moisture and prevents clumping .

Food Industry

STPP is a permitted food additive (INS 451i, EAFUS-listed) serving multiple technical functions including sequestrant, texturizer, emulsifier salt, stabilizer/thickener, humectant, and pH control agent . It is commonly used in:

• Processed meat and poultry products (as a moisture-retention agent)

• Seafood processing

• Dairy products and beverages

• Canned goods 

Water Treatment and Industrial Applications

• Water Softening: STPP sequesters calcium and magnesium hardness without precipitation .

• Dispersing Agent: Used in ceramic slurries, drilling muds, and pigment suspensions .

• Corrosion Inhibitor: Applied in steel treatment .

• Leather Pretanning and Dyeing Auxiliary .

Emerging Applications

Recent research has explored STPP's utility in:

• Dental Care: When added to low-fluoride toothpastes (as little as 0.25%), STPP can reduce enamel demineralization to levels comparable to conventional 1,100 ppm fluoride toothpaste .

• Nanoparticle Preparation: Used in the ionic gelation synthesis of chitosan nanoparticles .

• Pharmaceutical Buffers: Used to prepare buffer solutions in the pH 9.2-10.5 range .

Safety and Handling

• Hazard Classification: Classified as an irritant (Xi) with R36/37/38 (irritating to eyes, respiratory system, and skin) .

• Toxicity: Oral LD₅₀ in rats is 6.50 g/kg . Ingestion may cause violent purging and is moderately irritating to skin and mucous membranes .

• Storage: Should be stored in dry, well-ventilated areas, protected from moisture. Avoid contamination with acids or oxidizing agents .

• Transport: Protect from rain and moisture during transport .

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