Disodium phosphate
Disodium hydrogen phosphate (anhydrous) – Na₂HPO₄
Synonyms: disodium phosphate, disodium hydrogen phosphate, dibasic sodium phosphate; E339(ii) (food use)
INCI / functions: buffering (pH regulator / buffer), anticorrosive (packaging protection), support as a weak sequestrant (under specific conditions)
Definition
An inorganic phosphate-system salt, typically supplied in anhydrous form (Na₂HPO₄), used as a component of buffer solutions and as a pH regulator in aqueous formulations. From a compositional standpoint, the ingredient consists of sodium ions (Na⁺) and the hydrogen phosphate anion (HPO₄²⁻); controlled trace inorganic impurities may be present depending on grade (technical/food/pharma). In practice, it is often used together with monosodium phosphate (NaH₂PO₄) to obtain buffers in the neutral to slightly alkaline range.
Food: acidity regulator, stabilizer, technological aid (e.g., processed dairy systems, depending on category). In dietary supplements, disodium phosphate mainly serves both nutritional and technological functions. It is a source of phosphorus, which is essential for bone and teeth health. It contributes to energy metabolism through the role of phosphorus in ATP systems. It helps maintain proper electrolyte balance. It acts as a regulator of acid–base balance. It is used as a buffering agent to stabilize formulation pH. It supports the chemical stability of other ingredients. It can improve the solubility of certain nutrients. In some formulations, it may support intestinal function. It also plays a technological role in manufacturing support.
Cosmetics: pH buffer, aqueous-phase stability; also used as anticorrosive support to reduce corrosion phenomena related to packaging/metal contact.
Medical: use in buffer solutions and support preparations (technical-clinical context, per specifications).
Pharmaceutical: excipient for buffers, solutions and processing; supports stability of liquid dosage forms and certain manufacturing steps.
Industrial use: preparation of buffers for laboratory/industry and processes requiring aqueous pH control (sector-dependent requirements).
Calories (energy value)
| Metric | Value |
|---|
| Energy value (100 g) | 0 kcal (inorganic compound; provides no metabolizable energy) |
| Technical note | Technological use (pH / buffering), not nutritional |
Identification data and specifications
| Parameter | Value |
|---|
| Formula | Na₂HPO₄ |
| Molar mass | 141.96 g/mol |
| CAS number | 7558-79-4 |
| EC number | 231-448-7 |
| Food additive | E339(ii) |
| Property | Indicative value |
|---|
| Appearance | white crystals/powder |
| Odor | none |
| Water solubility (20–25 °C) | high (order of tens of g/L, grade- and temperature-dependent) |
| Ethanol solubility | practically insoluble |
| Typical pH (1–2% solution) | ~8.7–9.2 (indicative) |
| Hygroscopicity | moderate (manage moisture during storage) |
| Form | Details |
|---|
| Dihydrate form | Na₂HPO₄·2H₂O (CAS 10028-24-7, molar mass 177.99 g/mol) |
| Formulation note | anhydrous vs hydrate changes assay and weighing: for buffers and calculations always use the actual purchased form |
Phosphate buffer system (useful references)
| Parameter | Indicative values (25 °C) |
|---|
| Phosphoric system pKa values | pKa₁ ≈ 2.15; pKa₂ ≈ 7.20; pKa₃ ≈ 12.35 |
| Effective buffer window NaH₂PO₄ / Na₂HPO₄ | approx. pH 6.2–8.2 (highest efficiency around pKa₂) |
Functional role and “sequestrant” clarification
| Topic | Detail |
|---|
| Primary function | buffering: stabilizes pH by absorbing moderate acid/base additions |
| “Sequestrant” | interaction with Ca²⁺/Mg²⁺ is weak; in hard water and at higher pH it may promote precipitation (e.g., calcium phosphates) |
| Practical approach | if metal/hardness control is required, pair with sodium citrate or low-dose EDTA (depending on regulation and target) |
Formulation compatibility
| System | Compatibility | Control notes |
|---|
| Surfactants | generally excellent | verify systems with high cationic load |
| Polymers/gellants | often compatible | control viscosity and target pH (24–48 h maturation) |
| Pigments/minerals | compatible | caution with Ca²⁺-rich formulations (haze/precipitation risk) |
| pH-sensitive actives | useful | helps “lock” pH within narrow windows (validate specific compatibility) |
Use guidelines (indicative)
| Application | Typical range | Technical note |
|---|
| Leave-on / rinse-off cosmetics | 0.05–0.50% | fine pH trim and routine stability |
| Oral care (toothpastes/mouthwashes) | 0.2–2.0% | often paired with NaH₂PO₄ (typical pH target 6.0–7.5) |
| Food (E339(ii)) | category-dependent | dosage and conditions per applicable rules |
| Buffer preparation | — | dissolve salts separately, then combine under agitation; adjust pH with the acidic/basic partner and measure at stabilized temperature |
Practical phosphate buffer examples (purified water, 25 °C, indicative)
| Target pH | NaH₂PO₄ share | Na₂HPO₄ share | Note |
|---|
| ~6.5 | ~80–85% | ~15–20% | mass % on “anhydrous-equivalent” salts |
| ~7.0 | ~60–65% | ~35–40% | always bench-check (ionic strength/concentration matter) |
| ~7.4 | ~45–50% | ~50–55% | common near-physiological range (validate in system) |
| ~8.0 | ~25–30% | ~70–75% | higher risk with hard water (precipitation) |
Typical applications
Mild cleansers, shampoos, shower gels: pH stability and more consistent performance.
Gels and lotions: supports viscosity stability and pH-sensitive active stability.
Oral care: buffering for comfort and stability (within a coherent formulation design).
Food: acidity regulator/stabilizer; technological uses by category.
Quality, grades and specifications
| Topic | Detail |
|---|
| Grades | technical, food (E339(ii)), pharmaceutical |
| Typical controls | assay, insolubles, solution pH, moisture/loss on drying, trace metals |
| Operational note | select grade consistent with end use (food/pharma) and require an up-to-date CoA |
Safety, regulation and environment
| Topic | Operational guidance |
|---|
| Use safety | low toxicity at use levels; concentrated powder may irritate eyes/skin/respiratory tract |
| EU cosmetics | usable under general rules and GMP (verify finished formula compliance) |
| Food | E339(ii) additive with category-specific conditions of use |
| Environment | phosphates can contribute to eutrophication if released in quantity: manage effluents responsibly |
| Storage | sealed containers, cool dry place; avoid moisture and CO₂ uptake; keep away from strong acids |
Formulation troubleshooting
| Issue | Possible cause | Corrective actions |
|---|
| White haze/precipitates (hard water) | Ca²⁺ presence and elevated pH | lower target pH, reduce total phosphate, use deionized water; consider low-dose citrate/EDTA |
| pH drift after 24–48 h | dissolved CO₂, insufficient buffer capacity, temperature | increase buffer molarity, standardize temperature, re-tune with acid/base partner |
| Active incompatibilities | specific incompatibilities (cationics, metal salts, etc.) | run compatibility tests, optimize addition order and pH window |
Conclusion
Disodium phosphate (Na₂HPO₄) is a key ingredient for pH control in aqueous systems: reliable, predictable, and widely used in cosmetics, oral care, food, and technical/pharma contexts. Correct management of chemical form (anhydrous vs hydrate), water hardness, concentration, and the target pH window is essential to prevent instability (haze/precipitation) and achieve repeatable performance.
References__________________________________________________________________________
Huang C, Pettitt BM. Parameter Dependence of the Solubility Limit for Disodium Phosphate. J Phys Chem B. 2023 Oct 12;127(40):8690-8696. doi: 10.1021/acs.jpcb.3c05343.
Abstract. The solubility limit was calculated for supersaturated solutions of disodium phosphate in water as a function of the sodium-oxygen Lennard-Jones radius parameter Rmin. We found that changes in the sodium-oxygen Rmin were clearly exponentially related to the concentration of the solubility limit. Starting from standard force fields more suited to nucleic acids and phospholipids, only relatively small changes were required to achieve the experimentally known solubility limit. Simultaneously, we found that it was possible to achieve the solubility limit and the osmotic pressure with the same model parameters. Based on transferability, the adjusted Rmin parameter can be used to more accurately model phosphorylated proteins.
Buck CL, Wallman KE, Dawson B, Guelfi KJ. Sodium phosphate as an ergogenic aid. Sports Med. 2013 Jun;43(6):425-35. doi: 10.1007/s40279-013-0042-0.
Abstract. Legal nutritional ergogenic aids can offer athletes an additional avenue to enhance their performance beyond what they can achieve through training. Consequently, the investigation of new nutritional ergogenic aids is constantly being undertaken. One emerging nutritional supplement that has shown some positive benefits for sporting performance is sodium phosphate. For ergogenic purposes, sodium phosphate is supplemented orally in capsule form, at a dose of 3-5 g/day for a period of between 3 and 6 days. A number of exercise performance-enhancing alterations have been reported to occur with sodium phosphate supplementation, which include an increased aerobic capacity, increased peak power output, increased anaerobic threshold and improved myocardial and cardiovascular responses to exercise. A range of mechanisms have been posited to account for these ergogenic effects. These include enhancements in 2,3-Diphosphoglycerate (2,3-DPG) concentrations, myocardial efficiency, buffering capacity and adenosine triphosphate/phosphocreatine synthesis. Whilst there is evidence to support the ergogenic benefits of sodium phosphate, many studies researching this substance differ in terms of the administered dose and dosing protocol, the washout period employed and the fitness level of the participants recruited. Additionally, the effect of gender has received very little attention in the literature. Therefore, the purpose of this review is to critically examine the use of sodium phosphate as an ergogenic aid, with a focus on identifying relevant further research.
Dang JT, Moolla M, Dang TT, Shaw A, Tian C, Karmali S, Sultanian R. Sodium phosphate is superior to polyethylene glycol in constipated patients undergoing colonoscopy: a systematic review and meta-analysis. Surg Endosc. 2021 Feb;35(2):900-909. doi: 10.1007/s00464-020-07464-0.
Abstract. Background: Constipation is an important and highly prevalent predictor of inadequate bowel preparation during colonoscopy. In North America, between 2 and 28% of the general population suffer from constipation. Despite the high prevalence of constipation, to our knowledge, no meta-analysis on the optimal bowel preparation for constipated patients has been performed. We aimed to systematically review the literature to determine the ideal bowel preparation regiment for patients with chronic constipation. Methods: A comprehensive search of electronic databases (MEDLINE, EMBASE, SCOPUS, and Web of Science) was performed. We included studies that assessed the quality of bowel preparation in constipated patients receiving different agents prior to colonoscopy. The primary outcome was colon cleanliness. Secondary outcomes included tolerability of the bowel preparation and serious adverse events. Results: Preliminary database search yielded 1581 articles after duplicates were removed. After screening of the titles and abstracts using the exclusion criteria, 358 full-text articles were retained. Full-text articles were reviewed and eight studies meeting the inclusion criteria were included for qualitative synthesis. Three randomized controlled trials identified a total of 1636 constipated patients, of whom 225 were eligible for meta-analysis. Of those, 107 (47.6%) received NaP and 118 (52.4%) received PEG. Patients receiving NaP before colonoscopy had a higher chance of a successful bowel preparation than patients receiving PEG (OR 1.87, CI 1.06 to 3.32, P = 0.003). In the studies comparing PEG to NaP, two found that NaP resulted in greater tolerability of the bowel preparation and one study found that PEG resulted in superior tolerability. Conclusions: In chronically constipated patients undergoing colonoscopy, the use of NaP may result in superior colonic cleanliness when compared to PEG, however, quality of evidence was low. Further high-quality studies are required to delineate the optimal bowel preparation in patients with constipation.
Curran MP, Plosker GL. Oral sodium phosphate solution: a review of its use as a colorectal cleanser. Drugs. 2004;64(15):1697-714. doi: 10.2165/00003495-200464150-00009.
Abstract. Oral sodium phosphate solution (Fleet Phospho-soda, Casen-Fleet Fosfosoda is a low-volume, hyperosmotic agent used as part of a colorectal-cleansing preparation for surgery, x-ray or endoscopic examination. The efficacy and tolerability of oral sodium phosphate solution was generally similar to, or significantly better than, that of polyethylene glycol (PEG) or other colorectal cleansing regimens in patients preparing for colonoscopy, colorectal surgery or other colorectal-related procedures. Generally, oral sodium phosphate solution was significantly more acceptable to patients than PEG or other regimens. The use of this solution should be considered in most patients (with the exception of those with contraindications) requiring colorectal cleansing. PHARMACOLOGICAL PROPERTIES: After the first and second 45 mL dose of oral sodium phosphate solution, the mean time to onset of bowel activity was 1.7 and 0.7 hours and the mean duration of activity was 4.6 and 2.9 hours. Bowel activity ceased within 4 hours of administration of the second dose in 83% of patients. Elevations in serum phosphorus and falls in serum total and ionised calcium from baseline occurred during the 24 hours after administration of oral sodium phosphate solution in seven healthy volunteers. These changes were not associated with significant changes in clinical assessments. The decrease in serum potassium levels after administration of oral sodium phosphate solution was negatively correlated with baseline intracellular potassium levels.
Disodium phosphate 
Hydrogen phosphate anion
