Dibasic sodium phosphate
Sodium phosphate dibasic– Na₂HPO₄
Synonyms: disodium phosphate, disodium hydrogen phosphate; E339(ii) (food use)
INCI / functions: buffering (pH regulator), aqueous phase stability support, anticorrosive (packaging protection), processing aid in oral care
Definition
An inorganic, alkaline salt of the phosphate system, commonly supplied as Na₂HPO₄ (anhydrous form) or as hydrated forms (e.g., dihydrate). It appears as a white crystalline solid/white powder, odorless, and soluble in water. Its primary use is as a component of buffer solutions to maintain pH in the neutral to slightly alkaline range, typically paired with NaH₂PO₄ (monobasic sodium phosphate). It is used in cosmetics, oral care, food, and technical/laboratory applications where repeatable and robust pH control is required.
Calories (energy value)
0 kcal per 100 g (inorganic compound, provides no metabolizable energy).
Identification data and specifications
| Item | Value |
|---|---|
| Name | Dibasic sodium phosphate |
| English name | Sodium phosphate dibasic |
| Formula | Na₂HPO₄ |
| Molar mass | 141.96 g/mol |
| CAS number | 7558-79-4 |
| EC number | 231-448-7 |
| Common commercial form | Na₂HPO₄·2H₂O (dihydrate) |
| Molar mass (dihydrate) | 177.99 g/mol |
| CAS number (dihydrate) | 10028-24-7 |
| Property | Indication |
|---|---|
| Appearance | white crystals/powder |
| Odor | none |
| Water solubility (20–25 °C) | high (order of tens of g/L) |
| Alcohol solubility | insoluble / very low |
| Typical pH (aqueous solution) | ~8.7–9.3 (depends on concentration and grade) |
| Hygroscopicity | low to moderate (depends on form and grade) |
| Stability | stable at room temperature; avoid humidity and CO₂ if maximum pH repeatability is needed |
| Decomposition (approx.) | at elevated temperature (order ~250 °C) with possible condensed phosphate species |
| Acid–base parameters (25 °C, buffer reference) | Value |
|---|---|
| pKa₁ (H₃PO₄) | ≈ 2.15 |
| pKa₂ (H₃PO₄) | ≈ 6.8–7.2 |
| pKa₃ (H₃PO₄) | ≈ 12.3–12.4 |
| NaH₂PO₄ / Na₂HPO₄ buffering window | ~pH 6.2–8.2 (maximum effectiveness around pKa₂) |
Functional role and “chelating” clarification
The primary role is buffering: it keeps pH stable by absorbing moderate acidic or basic additions.
Its “metal control” effect is limited: in the presence of Ca²⁺/Mg²⁺ (hard water), phosphates can promote haze or precipitation (e.g., calcium phosphates) depending on pH and concentration. It is not a strong chelator (unlike citrates or EDTA). If hardness/metal management is required, formulators typically add a dedicated sequestrant (where allowed) and optimize pH.
Formulation compatibility
Surfactants: generally excellent with anionics, amphoterics, and many nonionics; verify with high-dosage cationic systems (ionic interactions).
Polymers and gelling agents: generally compatible; for pH-dependent systems, check viscosity and stability after 24–48 h.
Pigments/minerals: useful for aqueous phase stabilization; caution with calcium-rich systems (risk of opalescence/precipitates).
pH-sensitive actives: supports a narrow, repeatable pH window.
Use guidelines (indicative)
| Application | Typical range | Technical note |
|---|---|---|
| Leave-on / rinse-off cosmetics | 0.05–0.50% | fine pH trim and routine stability; increase if true buffer capacity is required |
| Oral care (toothpaste/mouthwash) | 0.2–2.0% | often paired with NaH₂PO₄ for pH 6.0–7.5 targets |
| Food (E339(ii)) | by category | comply with applicable requirements/limits for the specific category |
| Buffer procedure | Good practice |
|---|---|
| Preparation | dissolve salts separately, then combine under agitation |
| pH adjustment | small additions of the acid species (NaH₂PO₄) or the base species (Na₂HPO₄) |
| pH measurement | measure after thermal equilibrium and complete dissolution |
Practical phosphate buffer examples (25 °C, indicative)
| Target pH | NaH₂PO₄ (indicative fraction) | Na₂HPO₄ (indicative fraction) | Note |
|---|---|---|---|
| 6.5 | ~80–85% | ~15–20% | mass percentages as “anh.” salt equivalents |
| 7.0 | ~60–65% | ~35–40% | always verify at bench |
| 7.4 | ~45–50% | ~50–55% | typical “physiological” buffer |
| 8.0 | ~25–30% | ~70–75% | caution with hard water (Ca²⁺) |
Note: ionic strength and total concentration affect final pH; confirm in the real formulation.
Typical applications
Cleansers and toiletries: pH stability and more consistent performance when water quality varies.
Gels and lotions: supports chemical–physical stability and pH-sensitive actives.
Oral care: buffer systems and controlled comfort (managed pH).
Water-based make-up: pH control for dispersion stability and color performance.
Food: acidity regulator/stabilizer; established technological uses depending on category.
Quality, grades and specifications
| Grade | Typical use | Common checks |
|---|---|---|
| Technical | industrial applications | assay, insolubles, solution pH, inorganic impurities |
| Food (E339(ii)) | food processing | purity requirements, impurities, category-specific checks |
| Pharmaceutical / analytical | buffers and controlled preparations | tighter limits on impurities/metals, repeatability and traceability |
Note: for hydrated forms, loss on drying (water of crystallization) is also relevant.
Safety, regulation and environment
| Topic | Operational guidance |
|---|---|
| Toxicity | low at use levels; dust may irritate eyes and respiratory tract |
| Allergenicity | not typically associated with contact sensitization |
| EU cosmetics | generally usable; apply GMP and finished-formula safety assessment |
| Food | E339(ii) additive with category-based conditions of use |
| Environment | phosphates may contribute to eutrophication if released in quantity: manage effluents and process losses |
| Storage | airtight containers, cool and dry place; avoid humidity and CO₂; keep away from strong acids |
Formulation troubleshooting
| Issue | Possible cause | Corrective actions |
|---|---|---|
| White haze/precipitates | Ca²⁺ (hard water), high pH, excess phosphate | lower target pH, reduce phosphate, use deionized water, consider citrate/EDTA (where allowed) |
| pH drift after 24–48 h | insufficient buffer capacity, temperature, dissolved CO₂ | increase buffer “strength,” control temperature, re-balance with acid/base pair |
| Active interference | ionic incompatibility or pH sensitivity | compatibility testing, optimize addition order and neutralization, revise pH window |
Studies
Medical
Together with Monobasic Sodium Phosphate, it is used in both adults and children in evacuative solutions such as disposable enemas for the treatment of constipation, as a pH regulator and saline laxative, for the treatment of acute and chronic constipation and also for colon cleansing as a preparation for surgical procedures (1). These chemical compounds increase water content and stool volume, creating a rectal distension effect. The required effect is usually produced within about 5 minutes.
Dibasic sodium phosphate is also used as therapy in lead poisoning.
Dentistry
The incorporation of dibasic sodium phosphate as a buffering agent in the composition of the mineral trioxide aggregate is recognised as one of the solutions to improve its properties, reduce time and achieve a diametral tensile strength of 4.9 MPa at the initial 6-hour period.(2). Nucleating agent.
Human nutrition
The addition of dibasic sodium phosphate to meat increases the pH value and ionic strength of the meat, improving water retention and the overall yield of the final product.
Baking agent to prevent oxidation, emulsifier
Animal feed
Dibasic sodium phosphate is used for oral phosphorus supplementation in animal feed. In Qianbei-Pockmarked goats suffering from a disorder referred to as 'Ruanguzheng's disorder', disodium hydrogen phosphate supplementation prevented and cured the disorder (3).
Conclusion
Dibasic sodium phosphate is a key ingredient for pH control in aqueous formulations: predictable, cost-effective, and widely standardized. When used correctly as a buffer with NaH₂PO₄, it improves stability and repeatability in cosmetics and oral care, and it also delivers established technological functions in food. It does not replace a chelator: when needed, it should be combined with dedicated sequestrants and with careful management of pH, hardness, and concentration.
For more information:
Disodium hydrogen phosphate studies
Typical commercial product characteristics Sodium Phosphate, Dibasic
| Appearance | White crystal or powder, |
| pH | 8.8～9.2 |
| Boiling Point | 158ºC at 760 mmHg |
| Melting Point | 243-245°C |
| Density | 1.064 g/mL at 20°C |
| PSA | 93.23000 |
| Vapor density | 4.9 |
| Water Solubility | >=10 g/100 mL at 20ºC |
| Water insoluble | ≤ 0.4% |
| Loss on drying | ≤ 5.0% |
| Fluoride | ≤0.002% |
| Chloride | ≤ 0.06% |
| Sulphate | ≤ 0.2% |
| Arsenic | ≤ 0.0003% |
| Heavy Metals (As Pb) | ≤ 0.001% |
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Price
1 kg €168.00
12 kg €1,010.00
- Molecular Formula HO4PNa2 o HNa2O4P o Na2HPO4
- Molecular Weight 141.959
- Exact Mass 141.940781
- CAS 7558-79-4
- UNII 22ADO53M6F
- EC Number 231-448-7
- DSSTox Substance ID DTXSID1026039
- IUPAC disodium;hydrogen phosphate
- InChI=1S/2Na.H3O4P/c;;1-5(2,3)4/h;;(H3,1,2,3,4)/q2*+1;/p-2
- InChl Key BNIILDVGGAEEIG-UHFFFAOYSA-L
- SMILES OP(=O)([O-])[O-].[Na+].[Na+]
- MDL number MFCD00003496
- PubChem Substance ID 329824633
- ChEBI 34683
- FEMA 2398
- ICSC 1129
- RTECS WC4500000
- UN 3082
- eCl@ss 38070211
- NACRES NA.21
Synonyms
- Disodium Phosphate Dibasic
- Disodium hydrogenorthophosphate
- Disodium hydrogen phosphate
- Sodium phosphate dibasic
- DSHP
