Sodium hydroxide

• BPSodium Hydroxide
• JPSodium Hydroxide
• Ph. Eur.Sodium Hydroxide
• USP–NFSodium Hydroxide

Caustic soda; lye; natrii hydroxidum; soda lye; sodium hydrate; E524

Sodium hydroxide · [1310-73-2]

UNII 55X04QC32I · PubChem CID 14798

NaOH · 40.00

pH adjuster, buffering agent

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

Sodium hydroxide is widely used to adjust pH and to neutralise acids in parenteral, ophthalmic, oral and topical preparations, usually as a dilute solution and in very small amounts. It is used to form water-soluble salts of acidic drugs, to prepare buffer systems with weak acids, to neutralise carbomer dispersions to form gels, and to form soaps in situ with fatty acids in creams and emulsions.

White or almost white, hard, deliquescent pellets, flakes, sticks or fused masses. It is strongly alkaline and corrosive, and absorbs water and carbon dioxide rapidly from the air.

Melting point

318 °C

Solubility

very soluble in water, with strong evolution of heat; freely soluble in ethanol

pH

about 12 for a 0.05% w/v solution and about 13 for a 0.5% w/v solution

Density

about 2.1 g/cm³

Assay

pharmacopoeial material contains not less than about 97% total alkali as NaOH, including a limited amount of sodium carbonate

Sodium hydroxide absorbs moisture and carbon dioxide from the air, forming sodium carbonate. Store in an airtight, non-metallic container (such as polyethylene) in a cool, dry place. Solutions stored in glass slowly attack the glass.

Reacts violently with acids, liberating heat. Attacks aluminium, zinc and tin, producing flammable hydrogen. It hydrolyses esters, amides and many drugs, and may cause degradation or precipitation of alkali-sensitive drugs and excipients.

Produced industrially by electrolysis of sodium chloride solution (brine) in membrane, diaphragm or mercury cells, with chlorine and hydrogen as co-products; the solution is concentrated and the solid is obtained by evaporation.

In the small amounts used to adjust pH, sodium hydroxide is neutralised in the formulation and is not toxic. The solid and concentrated solutions are highly corrosive: they cause severe burns to the skin and eyes, and ingestion causes serious injury to the gastrointestinal tract.

Handle with great care. Wear chemical-resistant gloves, eye and face protection and protective clothing. Always add the solid slowly to water with stirring (never water to the solid), as the dissolution is strongly exothermic.

GRAS listed. Accepted as a food additive in Europe (E524). Included in the FDA Inactive Ingredient Database (injections, inhalation, nasal, ophthalmic, oral, otic, rectal, topical and vaginal preparations) and in parenteral and non-parenteral medicines licensed in Europe.

Potassium hydroxide; ammonia solution; trolamine.

For pH adjustment use freshly prepared or standardised dilute solutions (for example 0.1–1 M), since solutions absorb carbon dioxide and change strength. The final formulation records should state the amount of sodium hydroxide added or describe it as 'quantity sufficient to adjust pH'.