Sodium phosphate
Family of sodium salts of phosphoric acid: NaH₂PO₄ (monobasic), Na₂HPO₄ (dibasic), Na₃PO₄ (tribasic; often as hydrates)
Synonyms: monosodium phosphate (MSP), disodium phosphate (DSP), trisodium phosphate (TSP); food additives E339(i)–(iii)
INCI / Functions: pH buffer (pH adjuster), aqueous-phase stabilizer, processing aid in oral care, acidity regulator (food). TSP is strongly alkaline (mainly technical cleaning; limited cosmetic suitability).

Definition
“Sodium phosphate” refers to the sodium salts of phosphoric acid at different neutralization states. In water they form reliable buffer systems across a wide pH span. The most common grades for cosmetics, oral care, and foods are monosodium phosphate (NaH₂PO₄) and disodium phosphate (Na₂HPO₄; anhydrous or hydrates such as dihydrate/dodecahydrate). Trisodium phosphate (Na₃PO₄) is strongly alkaline and used chiefly in technical/cleaning applications or in regulated food uses.

Calories (energy value)
0 kcal per 100 g (inorganic salts provide no metabolizable energy).

Key identification (principal forms)

• NaH₂PO₄ (MSP) – acidic, highly water-soluble white crystals/powder; anhydrous or monohydrate.

• Na₂HPO₄ (DSP) – mildly alkaline, highly water-soluble white crystals/powder; anhydrous or hydrates (e.g., dihydrate/dodecahydrate).

• Na₃PO₄ (TSP) – strongly alkaline, very water-soluble white crystals; often as dodecahydrate.

Acid–base chemistry and buffering ranges
Phosphoric acid pKa at 25 °C: pKa₁ ≈ 2.15, pKa₂ ≈ 7.20, pKa₃ ≈ 12.35.

• NaH₂PO₄ / Na₂HPO₄ pair: optimal buffer around pH ~6.2–8.2 (ideal for cosmetic/oral-care systems).

• Na₂HPO₄ / Na₃PO₄ pair: buffers in the pH ~11–12 region (technical/cleaning; not for skin care).

Typical physicochemical properties (indicative)

• Appearance: white, odorless crystals/powders.

• Water solubility (25 °C): high for all forms; insoluble in ethanol.

• pH of aqueous solutions (1–2%):

  • MSP: ~4.3–4.8 (acidic)

  • DSP: ~8.7–9.2 (mildly alkaline)

  • TSP: ~11–12 (strongly alkaline)

• Hygroscopicity: moderate to marked for hydrates—store dry and sealed.

• Stability: hydrates lose crystal water on heating; dissolved CO₂ can shift pH slightly over time.

Functional role and note on “chelating”
The primary role in cosmetics/oral care is pH buffering. Interactions with Ca²⁺/Mg²⁺ are not true chelation; in alkaline or hard-water conditions phosphates may precipitate calcium/magnesium phosphates. For metal control/hardness, complement with sodium citrate or EDTA at low dose rather than relying on sodium phosphate alone.

Formulation compatibility

• Surfactants: excellent with anionics, amphoterics, and many nonionics; evaluate high-level cationics case-by-case.

• Polymers/gellants: compatible with neutralized carbomers, natural gums, and acrylates—respect the intended pH window.

• Pigments/minerals: stabilizes the aqueous phase; in Ca²⁺-rich systems watch for haze/precipitates.

• pH-sensitive actives: enables tight pH control for enzymes, fluorides (oral care), and color-critical systems.

Indicative use levels and handling

• Cosmetics (leave-on/rinse-off): 0.05–0.50% total phosphate salts for fine pH trim and routine stability.

• Oral care: 0.2–2.0% as MSP/DSP buffer targeting pH 6.0–7.5 with fluorides/antitartar systems.

• Food (E339): levels per category-specific regulations.

• Buffer preparation: dissolve acidic and basic salts separately, combine under stirring; adjust pH with small additions of MSP (acidic) or DSP (basic). Confirm after thermal equilibration.

Quick phosphate buffer recipes (purified water, 25 °C, indicative)

• pH ~6.5: 80–85% MSP + 15–20% DSP (mass of anhydrous equivalents).

• pH ~7.0: 60–65% MSP + 35–40% DSP.

• pH ~7.4: 45–50% MSP + 50–55% DSP.

• pH ~8.0: 25–30% MSP + 70–75% DSP.
  (Ionic strength/total concentration nudge the actual pH—always verify on bench.)

Typical applications

• Mild cleansers, shampoos, body washes: pH stability and consistent performance in hard water.

• Gels and lotions: viscosity and active stability in the aqueous phase.

• Oral care (toothpastes/mouthwashes): physiological pH buffering; supports antitartar strategies.

• Water-based make-up: pH stabilization for dispersion/colour.

• Food: acidity regulation/stabilization; emulsifying salts in processed cheese.

• Technical/industrial: TSP for degreasing/CIP (outside routine skin-care use due to high alkalinity).

Grades and specifications
Available as technical, food (E339), and pharmaceutical grades. Typical specs: assay, heavy metals (Pb, As, Cd) at very low limits, loss on drying (hydrates), solution pH, insolubles, and microbiological controls (food/pharma).

Safety, regulatory, and environmental notes

• Irritation: low at cosmetic levels; powders/concentrates can irritate eyes/skin/airways.

• Allergenicity: not a contact allergen.

• EU Cosmetics (Reg. 1223/2009): no specific restrictions for MSP/DSP; use per GMP and suitable pH targets.

• IFRA: not applicable (non-fragrance).

• Food: E339(i)–(iii); follow category limits/conditions.

• Environmental: phosphates may contribute to eutrophication—manage use and effluent responsibly.

• Storage: airtight, cool, dry; avoid moisture/CO₂ uptake; keep away from strong acids (neutralization).

Formulation troubleshooting

• White haze/precipitates in hard water: lower target pH, reduce phosphate level, add citrate/EDTA at low dose, or switch to DI water.

• pH drift over 24–48 h: recheck buffer capacity (total molarity), temperature, and dissolved CO₂; re-trim with small acidic/basic component additions.

• Active interactions: verify with enzymes, aluminum salts (antiperspirants), and high-level cationics; optimize order of addition.

What it is used for and where

It has many applications:

• In medicine to combat lead poisoning and in cases of phosphorus deficiency.
• In the textile industry to make fabrics less flammable.
• In the ceramic glaze industry.
• In the food industry as a buffer and neutralizer.
• In agriculture  as a fertilizer.
• In veterinary medicine, as a laxative.

Cosmetics

Disodium phosphate in cosmetics, it is an acidity regulator, enhances the antioxidant action of other ingredients and prevents the formation of lumps.

• Buffering agent. An ingredient that can bring an alkaline or acid solution to a certain pH level and prevent it from changing. in practice a pH stabiliser.
• Corrosion inibitor
• Fragrance. It plays a very important role in the formulation of cosmetic products as it allows perfume to be enhanced, masked or added to the final product, improving its commercial viability.  The consumer always expects to find a pleasant scent in a cosmetic product.
• pH adjuster. This ingredient tends to restore the pH of a cosmetic formulation to its optimal value. The correct pH value is an essential determinant for lipid synthesis in the stratum corneum. The average physiological pH value of the face ranges between 5.67 and 5.76. The hair fibre has a pH value of 3.67.

Conclusion
Sodium phosphate denotes a workhorse family of buffering salts. In cosmetics and oral care, the MSP/DSP pair is a gold-standard tool for stable pH control, broad compatibility, and industrial repeatability. For true metal management, complement with sodium citrate or EDTA; reserve TSP for technical/high-alkalinity contexts. With thoughtful control of pH, hardness, concentration, and storage, sodium phosphates underpin stable, safe, and compliant water-based products. 

Disodium phosphate studies

• Molecular Formula: HNa₂O₄P
• Molecular Weight: 141.957 g/mol
• CAS: 7558-79-4
• EC Number: 231-448-7
• UNIII: 22ADO53M6F
• FEMA Number: 2398

• dibasic sodium phosphate, anhydrous
• phosphoric acid, disodium salt, heptahydrate
• disodium acid phosphate
• phosphoric acid, monosodium salt
• disodium hydrogen phosphate
• phosphoric acid, monosodium salt, anhydrous
• disodium hydrogen phosphate anhydrous
• phosphoric acid, sodium salt
• monosodium dihydrogen phosphate
• phosphoric acid, trisodium salt
• neutral sodium hydrogen phosphate
• phosphoric acid, disodium salt
• phosphoric acid, disodium salt, 32P-labeled
• phosphoric acid, disodium salt, anhydrous
• phosphoric acid, disodium salt, dodecahydrate

References__________________________________________________________________________

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.

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. Therapeutic use: A regimen that administered the first dose of sodium phosphate on the previous evening and a second dose on the morning of the procedure (10-12 hours apart) was significantly more effective than PEG-based regimens for colorectal cleansing in preparation for colonoscopy, sigmoidoscopy or colorectal surgery. A regimen that administered both doses of oral sodium phosphate on the day prior to the procedure offered no colorectal cleansing advantage over PEG-based regimens and was significantly less effective than an oral sodium phosphate solution regimen that administered one dose on the previous evening and a second dose on the morning of the procedure. Oral sodium phosphate solution was generally as effective as other colorectal cleansing solutions (including magnesium citrate-containing regimens with sodium picosulfate). The direct costs of a diagnostic colonic examination with oral sodium phosphate solution were less than those with PEG (US465 dollars vs US503 dollars per patient; 1995 values), according to data from a US study. Oral sodium phosphate solution was significantly more effective than a commercially available tablet formulation as a colorectal cleanser prior to colonoscopy (data from one study only). Tolerability: Oral sodium phosphate solution administered as two 45 mL doses (generally 10-12 hours apart) was well tolerated in well designed trials in which adults with major comorbid conditions were excluded. Sodium phosphate-associated adverse events were mostly gastrointestinal (including abdominal pain/cramping, abdominal fullness and/or bloating, anal or perianal irritation or soreness, nausea, vomiting or hunger pains), although dizziness, weakness/fatigue, thirst, chest pain, chills, headache and sleep loss were also reported. Faecal incontinence was commonly reported in the elderly. Three doses (administered 10 minutes apart) of 15 mL of oral sodium phosphate solution, each diluted in 250 mL of clear fluid was associated with less vomiting than one 45 mL dose of the solution diluted in 250 mL of clear fluid (data from one study). In patients without major comorbid conditions, oral sodium phosphate has been associated with transient and clinically inconsequential changes in intravascular volume and electrolyte disturbances. Serious electrolyte disturbances have been associated with oral sodium phosphate administration in patients in whom sodium phosphate is contraindicated or should be use with caution (the elderly and those with bowel obstructions, small intestinal disorders, poor gut motilderly and those with bowel obstructions, small intestinal disorders, poor gut motility, renal insufficiency, cardiovascular disease or taking concomitant medication) or in patients ingesting more than the recommended dosage. Changes in the colonic mucosa have been reported in patients treated with oral sodium phosphate solution; however, the exact role of this agent in the appearance of these changes has not been fully clarified. The tolerability profile of oral sodium phosphate solution was similar to, or significantly better than, that of PEG or other colorectal cleansing regimens. Oral sodium phosphate solution was generally significantly more acceptable than PEG or other colorectal cleansing regimens. Oral sodium phosphate solution had similar tolerability, but was considered to be more acceptable than commercially available oral sodium phosphate tablets prior to colonoscopy (data from one study).

Cheng J, Tao K, Shuai X, Gao J. Sodium phosphate versus polyethylene glycol for colonoscopy bowel preparation: an updated meta-analysis of randomized controlled trials. Surg Endosc. 2016 Sep;30(9):4033-41. doi: 10.1007/s00464-015-4716-6. 

Abstract. Background: Adequate bowel cleansing is of great importance for a high-quality colonoscopy examination. Nevertheless, whether sodium phosphate or polyethylene glycol is a gold standard agent for bowel preparation is still under debate. In consideration of the clinical needs, we thus performed an updated meta-analysis of randomized controlled trials concerning the comparison between both regimens. The efficacy, safety and acceptability of each regimen are major indicators to measure and appraise. Methods: By searching PubMed, EMBASE, Web of Science and Cochrane Library databases, 15 original trials published from 2000 to 2014 were included as eligible studies. We carried out data extraction and subsequent pooling analysis for each indicator in a standard manner. Sensitivity analysis was performed by elimination of low-quality trials, while a funnel plot and Egger's test were employed to analyze the publication bias across studies. Results: Our pooling analysis revealed that patients undergoing sodium phosphate as a cleansing agent displayed better acceptability, compliance, cleansing scores, preparation taste, polyp detection rate and less adverse effects including nausea, vomiting and abdominal pain (P < 0.05). In terms of procedure time, adequate preparation rate and electrolyte concentration, there was no significant difference between both regimens (P > 0.05). The pooling analysis offered stable conclusions which were verified by our sensitivity analysis. There was no publication bias across studies as a symmetric funnel plot was demonstrated and the result of Egger's test was P = 0.56. Conclusions: Regarding preparation efficacy, safety and acceptability, sodium phosphate was a better agent than polyethylene glycol for colonoscopy bowel cleansing, with its advantages of higher efficacy, better tolerability and acceptability as well as comparable safety.

Hoffmanová I, Kraml P, Anděl M. Renal risk associated with sodium phosphate medication: safe in healthy individuals, potentially dangerous in others. Expert Opin Drug Saf. 2015 Jul;14(7):1097-110. doi: 10.1517/14740338.2015.1044970. 

Abstract. Introduction: Sodium phosphate purgatives are used for bowel preparation before endoscopic or radiologic examination and occasionally for treatment of severe obstipation. Generally, they are well tolerated and effective; however, safety concerns exist regarding serious renal injury and electrolyte disturbances after administration of these drugs. Areas covered: The review presents complications associated with the use of agents containing sodium phosphate with regard to electrolyte disorders and renal impairment, namely acute phosphate nephropathy (APhN). This paper discusses the pathophysiology, histopathological findings, clinical symptoms, diagnosis and treatment of APhN. Additionally, it examines the epidemiology of adverse renal events and the safety of using sodium phosphate preparations prior to colonoscopy. Expert opinion: Because of safety concerns, sodium phosphate purgatives are not recommended for routine bowel cleansing. Despite some serious and even fatal adverse events associated with these drugs when used with at-risk patients, available data suggest that administration of sodium phosphate purgatives is relatively safe in nonrisk individuals(i.e., in adequately hydrated, otherwise healthy adults, younger than 55 years with evidence of normal renal function).