Sodio fosfato
Famiglia di sali di sodio dell’acido fosforico: NaH₂PO₄ (monobasico), Na₂HPO₄ (bibasico), Na₃PO₄ (tribasico; spesso come dodecaidrato)
Sinonimi: fosfato monosodico (MSP), fosfato disodico (DSP), fosfato trisodico (TSP); in ambito alimentare: E339(i)–(iii)
INCI / Funzioni: regolatore di pH (tampone), stabilizzante di fase acquosa, coadiuvante in oral care, correttore di acidità (food); il TSP è basificante/chelante debole e detergente tecnico (uso cosmetico limitato per alcalinità)

Definizione
Con “sodio fosfato” si indicano i sali sodici dell’acido fosforico in diversi gradi di neutralizzazione. In acqua generano sistemi tampone molto affidabili su un ampio intervallo di pH. Le forme più usate in cosmetica, oral care e food sono il fosfato monosodico (NaH₂PO₄) e il fosfato disodico (Na₂HPO₄, anidro o diidrato/ dodecaidrato); il fosfato trisodico (Na₃PO₄) è fortemente alcalino, impiegato soprattutto in ambiti tecnici/detergenza o in alimentare con condizioni specifiche.

Calorie (valore energetico)
0 kcal per 100 g (sali inorganici privi di energia metabolizzabile).

Dati di identificazione (forme principali)

• NaH₂PO₄ (fosfato monosodico; anidro o monoidrato): solido cristallino acido, molto solubile.

• Na₂HPO₄ (fosfato disodico; anidro/ diidrato/dodecaidrato): solido cristallino leggermente alcalino, altamente solubile.

• Na₃PO₄ (fosfato trisodico; spesso dodecaidrato): solido cristallino fortemente alcalino, molto solubile.

Chimica acido-base e intervalli tampone

• Costante di dissociazione dell’acido fosforico (25 °C): pKa₁ ≈ 2,15, pKa₂ ≈ 7,20, pKa₃ ≈ 12,35.

• Coppia NaH₂PO₄ / Na₂HPO₄: tampone ottimale pH ~6,2–8,2 (medico-cosmetico/oral care).

• Coppia Na₂HPO₄ / Na₃PO₄: tampone pH ~11–12 (ambiti tecnici; non per skin-care).

Proprietà fisico-chimiche (indicative)

• Aspetto: polveri/cristalli bianchi, inodori.

• Solubilità in acqua (25 °C): elevata per tutte le forme; insolubili in etanolo.

• pH soluzione acquosa:

  • NaH₂PO₄ (1–2%): ~4,3–4,8 (acido).

  • Na₂HPO₄ (1–2%): ~8,7–9,2 (alcalino lieve).

  • Na₃PO₄ (1%): ~11–12 (alcalino forte).

• Igroscopicità: da moderata a marcata (idrati); conservare chiuso e asciutto.

• Stabilità: gli idrati perdono acqua per riscaldamento; CO₂ disciolta può spostare il pH.

Ruolo funzionale e note su “sequestrazione”
Il ruolo primario dei fosfati sodici in cosmetica/oral care è tampone pH. L’interazione con Ca²⁺/Mg²⁺ può dare precipitazione di fosfati di calcio/magnesio in condizioni alcaline o acque dure: non sono chelanti forti (come citrati o EDTA). Per controllo dei metalli/durezza si associano citrato di sodio o EDTA a basso dosaggio.

Compatibilità formulativa

• Tensioattivi: ottima con anionici/anfoteri/non-ionici; valutare cationici ad alto dosaggio.

• Polimeri: compatibili con carbomeri neutralizzati, gomme naturali, acrilati (rispettare finestra pH).

• Pigmenti/minerali: stabilizzano la fase acquosa; attenzione ai sistemi ricchi di Ca²⁺ (velature/precipitati).

• Attivi pH-sensibili: utili per enzimi, fluoruri (oral care), sistemi colore.

Linee guida d’uso (indicative)

• Cosmetica (leave-on / rinse-off): 0,05–0,50% di Na₂HPO₄ e/o NaH₂PO₄ per fine pH-trim e stabilità.

• Oral care: 0,2–2,0% in coppia tampone (pH target 6,0–7,5) con fluoruri/antitartaro.

• Alimentare (E339): dosi per categoria di alimento secondo normativa.

• Na₃PO₄ (TSP): l’alcalinità elevata lo rende non idoneo a tipiche formule skin-care; uso prevalentemente tecnico/detergenza o condizioni regolamentate in food.

Ricette pratiche di tamponi fosfato (25 °C; acqua purificata; valori indicativi)

• pH ~6,5: 80–85% NaH₂PO₄ + 15–20% Na₂HPO₄ (in massa “equivalenti anidri”).

• pH ~7,0: 60–65% NaH₂PO₄ + 35–40% Na₂HPO₄.

• pH ~7,4: 45–50% NaH₂PO₄ + 50–55% Na₂HPO₄.

• pH ~8,0: 25–30% NaH₂PO₄ + 70–75% Na₂HPO₄.
  (Forza ionica e concentrazione spostano lievemente il pH: verificare sempre a banco.)

Applicazioni tipiche

• Detergenti delicati, shampoo, bagnodoccia: pH stabile e performance costante in acque dure.

• Gel/lozioni: controllo viscosità e stabilità attivi idrofili.

• Oral care (dentifrici/collutori): tampone vicino al fisiologico; supporto antitartaro.

• Make-up acquoso: stabilità di dispersioni/pigmenti.

• Alimentare: regolatore acidità/stabilizzante; emulsifying salts (formaggi fusi).

• Tecnico/industriale: con Na₃PO₄ per sgrassatura/clean-in-place (fuori dall’ambito cosmetico di routine).

Qualità e specifiche
Disponibili gradi tecnico, alimentare (E339) e farmaceutico. Parametri tipici: titolo, metalli pesanti (Pb, As, Cd) a livelli molto bassi, perdita all’essiccamento (idrati), pH soluzione, insolubili, carica microbica (food/pharma).

Sicurezza, normativa e ambiente

• Irritazione: bassa ai dosaggi cosmetici; polveri concentrate possono irritare occhi/pelle/vie aeree.

• Allergenicità: non note reazioni allergiche da contatto.

• Cosmetici UE (Reg. 1223/2009): nessuna restrizione specifica per NaH₂PO₄/Na₂HPO₄; uso secondo GMP e pH idonei.

• IFRA: non applicabile (non è fragranza).

• Alimentare: E339(i)–(iii); rispettare limiti/condizioni per categoria.

• Ambientale: i fosfati possono contribuire a eutrofizzazione; gestire dosi e scarichi in modo responsabile.

• Stoccaggio: contenitori ermetici, luogo fresco e asciutto; evitare assorbimento di umidità/CO₂; lontano da acidi forti (neutralizzazione).

Troubleshooting formulativo

• Precipitati/velature bianche (acque dure): ridurre pH target, abbassare livello di fosfato, aggiungere citrato/EDTA a basse dosi o usare acqua deionizzata.

• Deriva di pH a 24–48 h: rivedere forza tampone (molarità totale), temperatura, CO₂ disciolta; rifinire con piccole aggiunte della componente acida/basica.

• Interazioni con attivi: verificare compatibilità con enzimi, sali di alluminio (antitraspiranti) e cationici concentrati; ottimizzare l’ordine di aggiunta.

Conclusione
Il termine sodio fosfato copre una famiglia di sali estremamente utili in formulazione. In cosmetica e oral care, la coppia NaH₂PO₄/Na₂HPO₄ è uno standard di riferimento per garantire pH stabili, buona compatibilità e ripetibilità industriale. Per esigenze di chelazione o durezza si affiancano citrato o EDTA, mentre l’uso del TSP resta confinato a scenari tecnici/alcalini. Con una corretta gestione di pH, durezza, concentrazione e stoccaggio, i fosfati di sodio assicurano prodotti stabili, sicuri e conformi. 

Sodio fosfato studi

• Formula molecolare: HNa₂O₄P
• Peso molecolare: 141.957 g/mol
• CAS: 7558-79-4    7782-85-6     10140-65-5 
• EC Number:231-448-7
• UNIII:22ADO53M6F
• FEMA Number: 2398

Sinonimi: 

• 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

Bibliografia__________________________________________________________________________

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).