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Views: 0 Author: Site Editor Publish Time: 2026-08-07 Origin: Site
Sodium Phosphate Monobasic Monohydrate (chemical formula NaH₂PO₄·H₂O, CAS Number 10049-21-5) is an inorganic phosphate salt widely used across food processing, water treatment, agriculture, metal finishing, ceramics, and laboratory applications.
It is also known by several common names:
Synonym | Usage Context |
Monosodium phosphate (MSP) | General industrial & food |
Sodium dihydrogen phosphate monohydrate | Laboratory & analytical |
E339(i) | EU food additive designation |
MSP monohydrate | Animal feed & fertilizer |
Primary sodium phosphate | Older nomenclature |
At room temperature, it appears as a white crystalline powder or colorless crystals, is highly soluble in water (~1103 g/L at 20 °C), and exhibits mildly acidic behavior in aqueous solution (pH ~4.4–4.5). The compound has a molecular weight of 137.99 g/mol and an EC Number of 231-449-2.
Understanding the physicochemical profile of NaH₂PO₄·H₂O is critical for proper handling, storage, and formulation in industrial processes.
Property | Value |
Chemical Formula | NaH₂PO₄·H₂O |
Molecular Weight | 137.99 g/mol |
CAS Number | 10049-21-5 |
EC Number | 231-449-2 |
Appearance | White crystalline powder or granules |
Solubility in Water | ~1103 g/L at 20 °C |
pH (1% solution) | 4.4 – 4.5 |
Melting Point | ~100 °C (loses water of crystallization); anhydrous form melts at ~650 °C |
Density | ~2.357 g/cm³ (at 20.5 °C) |
Storage Condition | Cool, dry, well-ventilated area; keep container tightly closed |
The monohydrate form contains one molecule of water of crystallization. Upon heating above 100 °C, it loses this water and converts to the anhydrous form (NaH₂PO₄), which is stable up to much higher temperatures. This thermal behavior is important for applications involving heated processes such as ceramic glazing, enamel manufacturing, and certain detergent formulations.
One of the largest industrial uses of sodium phosphate monobasic monohydrate is in water treatment systems, particularly for corrosion control and scale inhibition:
Boiler Water Treatment:MSP is dosed into boiler feed water to maintain a controlled pH and precipitate calcium and magnesium ions as soft phosphate sludge rather than hard scale. This protects boiler tubes from scaling and extends equipment service life.
Cooling Water Systems:In recirculating cooling towers, MSP acts as a corrosion inhibitor for ferrous metals by forming a protective phosphate film on metal surfaces.
Potable Water Distribution:Combined with polyphosphates, MSP helps control "red water" (iron corrosion) and "blue water" (copper corrosion) in municipal water distribution networks.
In the metal finishing industry, NaH₂PO₄·H₂O serves multiple functions:
Phosphating / Parkerizing:As a key component in metal pretreatment baths, MSP provides the phosphate ions needed to form a crystalline phosphate conversion coating on steel, iron, and zinc surfaces. This coating improves paint adhesion and provides a base for subsequent organic coatings or lubricants.
Electroplating Baths:MSP functions as a buffering agent in nickel, chromium, and zinc electroplating solutions, stabilizing pH during deposition and ensuring consistent plating quality.
Acid Cleaning & Pickling:Formulated into acid-based metal cleaners, MSP enhances cleaning efficiency while providing some corrosion inhibition on cleaned metal surfaces.
Soldering & Brazing Flux:MSP can partially substitute borax in certain soldering and brazing flux formulations, providing a clean oxide-removing action at elevated temperatures.
In ceramics manufacturing, monobasic sodium phosphate acts as a dispersant and deflocculant in clay slurries, improving the flow properties of ceramic slips for casting. In enamel frits, it contributes phosphorus content that modifies gloss, opacity, and adhesion characteristics of the final enamel coating.
MSP is incorporated into industrial and institutional cleaning formulations for several reasons:
Builder / Sequestrant:It chelates hardness ions (Ca²⁺, Mg²⁺) in wash water, softening it and improving detergent performance.
pH Buffering:It stabilizes the alkaline pH of cleaning solutions, maintaining cleaning efficacy throughout the wash cycle.
Anti-redeposition:Helps keep soil particles suspended in wash water, preventing them from settling back onto cleaned surfaces.
Mordant in Dyeing:MSP acts as a mordant, helping fix dyes to textile fibers and improving color fastness.
Weighting Silk:Historically and in certain specialty applications, MSP is used in the weighting process for silk to add body and drape.
Flame Retardant Treatment:Phosphates, including MSP, are applied as flame-retardant finishes on certain textiles.
In leather tanning, MSP participates in deliming and buffering processes, helping control pH during various stages of hide processing.
Sodium phosphate monobasic monohydrate is approved as a food additive in most jurisdictions. In the European Union, it is designated as E339(i) under the category "Sodium Phosphates." The FDA in the United States recognizes it as Generally Recognized as Safe (GRAS) for its intended food uses.
Function | How It Works | Typical Food Products |
Acidity Regulator / pH Buffer | Maintains a consistent pH range in food systems | Carbonated beverages, fruit juices, sauces |
Emulsifying Agent | Helps disperse fat droplets in aqueous phases, preventing separation | Processed cheese, dairy spreads, salad dressings |
Water Binding / Moisture Retention | Increases water-holding capacity of proteins | Processed meats (sausages, ham), poultry, seafood |
Sequestrant | Binds metal ions that can catalyze oxidation or discoloration | Canned seafood, processed fruits & vegetables |
Leavening Acid | Reacts with sodium bicarbonate to release CO₂ | Baking powders, self-rising flours, cake mixes |
Texturizer | Modifies protein structure for desired mouthfeel | Imitation dairy products, processed cheese slices |
In processed cheese manufacturing, MSP (often in combination with other phosphate salts) is essential for:
● Emulsifying fat into the protein matrix, creating a smooth, homogeneous texture
● Preventing oil separation during heating and cooling cycles
● Adjusting pH to optimize melt characteristics
● Extending shelf life by inhibiting microbial growth through pH control
Monosodium phosphate is used as a high-analysis phosphorus fertilizer, supplying both phosphorus (P) and sodium (Na) to crops. It is particularly valuable in:
Fertigation systems
● (fertilizer injected through irrigation) due to its excellent water solubility
Foliar sprays
● for rapid phosphorus uptake through leaves
NPK compound fertilizer formulations
● as a phosphorus source
Hydroponic nutrient solutions
● where precise P and Na dosing is required
MSP-based fertilizers contain approximately 22–23% phosphorus (as P₂O₅) and are fully water-soluble, making them suitable for drip irrigation and other precision agriculture applications.
In livestock and poultry nutrition, MSP is used as a feed-grade phosphorus supplement:
Livestock | Benefit |
Dairy Cattle | Supports milk production; phosphorus is critical for energy metabolism |
Beef Cattle | Promotes bone development and growth rates |
Poultry (Broilers & Layers) | Essential for skeletal development and eggshell quality |
Swine | Improves feed conversion ratio and growth performance |
Aquaculture (Fish & Shrimp) | Readily bioavailable phosphorus source in formulated feeds |
Equine | Supports bone density and metabolic functions in performance horses |
In feed formulations, MSP provides a highly bioavailable source of phosphorus — superior to many rock-phosphate-derived supplements — along with supplemental sodium. Typical inclusion rates vary by species and production stage, generally in the range of 0.2–1.0% of total feed dry matter.
The monohydrate form (NaH₂PO₄·H₂O) contains one water molecule per formula unit and has a molecular weight of 137.99 g/mol. The anhydrous form (NaH₂PO₄) has a molecular weight of 119.98 g/mol. When substituting one for the other in formulations, a weight correction factor of approximately 1.15 must be applied (monohydrate → anhydrous) or 0.87 (anhydrous → monohydrate).
Yes. "Monosodium phosphate" (MSP), "sodium dihydrogen phosphate," and "sodium phosphate monobasic" are all synonyms referring to NaH₂PO₄ and its hydrated forms.
Yes, when manufactured to food-grade specifications (meeting FCC, JECFA, or EU 231/2012 standards), it is approved as food additive E339(i) and is widely used as an acidity regulator, emulsifier, and moisture retention agent in processed foods.
A typical 0.1 M phosphate buffer at pH 7.0 can be prepared by dissolving approximately 4.4 g of NaH₂PO₄·H₂O and 5.8 g of Na₂HPO₄ (anhydrous) in 1 liter of deionized water. Adjust the ratio of monobasic to dibasic salts to achieve the target pH. Always verify with a calibrated pH meter.
Standard packaging includes 25 kg multi-wall paper bags with inner PE liner, 50 lb bags (North American market), 1000 kg (1 MT) supersacks / FIBCs (flexible intermediate bulk containers), and bulk tanker shipments for large-volume consumers. Custom packaging is available from most major manufacturers upon request.
When stored under recommended conditions (cool, dry, sealed container), the typical shelf life is 24–36 months from the date of manufacture. Product should be retested after the manufacturer's recommended retest date before use in critical applications.
Industrial / Technical Grade
● is suitable for water treatment, metal finishing, ceramics, detergents, and non-food-contact applications. It allows higher impurity levels and lower purity.
Food Grade (FCC/E339i)
● is mandatory for any application where the chemical comes into direct contact with food or food ingredients.
Never use industrial-grade MSP in food applications, as it may contain impurities that do not meet food safety standards.
