Sodium phosphate, dibasic

• JPDibasic Sodium Phosphate Hydrate
• Ph. Eur.Disodium Phosphate Dihydrate
• Ph. Eur.Disodium Phosphate Dodecahydrate
• Ph. Eur.Disodium Phosphate, Anhydrous
• USP–NFDibasic Sodium Phosphate

Disodium hydrogen phosphate; disodium hydrogen orthophosphate; disodium phosphate; natrii phosphas; phosphoric acid disodium salt; secondary sodium phosphate; E339(ii)

Disodium hydrogen phosphate (anhydrous or as the dihydrate, heptahydrate or dodecahydrate) · [7558-79-4]

UNII 22ADO53M6F · PubChem CID 24203

Na2HPO4 (anhydrous); Na2HPO4·2H2O; Na2HPO4·7H2O; Na2HPO4·12H2O · 141.96 (anhydrous); 177.99 (dihydrate); 268.07 (heptahydrate); 358.14 (dodecahydrate)

pH adjuster, buffering agent

Typical concentrations: — · Dosage forms: Liquid, Sterile (parenteral/ophthalmic)

Dibasic sodium phosphate is used widely as a buffering agent, usually in combination with monobasic sodium phosphate to give phosphate buffers in the pH range of about 6–8, in parenteral, ophthalmic, nasal, oral and topical preparations and in biologics. It is also used as a sequestering agent and as a source of phosphate, and it is used therapeutically as a saline laxative and phosphate supplement. Buffer concentrations are usually low (of the order of 0.1–1% w/v).

The anhydrous form is a white, hygroscopic powder. The dihydrate is a white or almost white crystalline powder or colourless crystals, the heptahydrate occurs as colourless crystals or a granular powder, and the dodecahydrate as colourless, transparent, strongly efflorescent crystals. All are odourless with a saline taste.

pKa values (phosphoric acid)

about 2.1, 7.2 and 12.3 at 25 °C

pH

about 9 (1% w/v aqueous solution)

Solubility

freely soluble in water (more so in hot water); practically insoluble in ethanol

Hydrate behaviour

the dodecahydrate effloresces in air and melts at about 35 °C; the anhydrous form absorbs moisture

Chemically stable. The hydrates gain or lose water depending on temperature and humidity, so the water content can change on storage; heating at high temperatures converts it to sodium pyrophosphate. Aqueous solutions are stable and may be sterilised by autoclaving. Store in an airtight container in a cool, dry place.

Incompatible with alkaloids, antipyrine, chloral hydrate, lead acetate, pyrogallol and resorcinol, and with calcium and magnesium salts, with which it forms insoluble phosphates (for example calcium phosphate precipitation in parenteral nutrition mixtures). Interactions between calcium, magnesium and phosphate can also lead to insoluble complexes in other formulations.

Prepared by partial neutralisation of phosphoric acid with sodium carbonate or sodium hydroxide to the appropriate stoichiometry; the hydrates are obtained by crystallisation and the anhydrous form by drying.

Generally regarded as non-toxic at the levels used as a buffer. Large oral doses act as an osmotic laxative, and excessive intake or administration, particularly in patients with renal impairment or in bowel-cleansing regimens, can cause hyperphosphataemia, hypocalcaemia and acute phosphate nephropathy.

Observe normal precautions for the quantity handled. Eye protection and gloves are recommended.

GRAS listed. Accepted as a food additive in Europe (E339). Included in the FDA Inactive Ingredient Database (injections, inhalation, nasal, ophthalmic, oral, otic, topical and vaginal preparations) and in parenteral and non-parenteral medicines licensed in Europe.

Sodium phosphate, monobasic; potassium phosphate, dibasic; trisodium phosphate.

Always state which hydrate is used and calculate quantities on that basis, since the dodecahydrate contains about 60% water. Phosphate buffers can crystallise selectively during freezing, causing large pH shifts in frozen and lyophilised protein formulations.