Citric acid

• BPCitric Acid
• JPAnhydrous Citric Acid
• Ph. Eur.Citric Acid
• USP–NFCitric Acid, Anhydrous

2-hydroxy-1,2,3-propanetricarboxylic acid; acidum citricum; citric acid monohydrate; anhydrous citric acid; E330

2-Hydroxypropane-1,2,3-tricarboxylic acid (anhydrous or monohydrate) · [77-92-9]

UNII XF417D3PSL · PubChem CID 311

C6H8O7 (anhydrous); C6H8O7·H2O (monohydrate) · 192.12 (anhydrous); 210.14 (monohydrate)

pH adjuster, buffering agent, Antioxidant, chelating agent

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

Widely used as an acidifier, buffer component (with sodium citrate), flavour enhancer and chelating antioxidant synergist in oral, topical and parenteral products, cosmetics and foods. Typical concentrations: buffer solutions 0.1–2.0%; flavour enhancer in oral liquids 0.3–2.0%; sequestering agent 0.3–2.0%. In effervescent tablets and granules it is combined with sodium bicarbonate or carbonate as the acid source, at much higher proportions.

Colourless or translucent crystals, or a white crystalline powder, odourless with a strongly acidic taste. The monohydrate is efflorescent in dry air.

pKa

3.13, 4.76 and 6.40 (25 °C)

Melting point

anhydrous about 153 °C; the monohydrate loses water and melts at about 100 °C

pH

about 2.2 (1% w/v aqueous solution)

Density

about 1.67 g/cm³ (anhydrous); about 1.54 g/cm³ (monohydrate)

Solubility

very soluble in water; freely soluble in ethanol; sparingly soluble in ether

The monohydrate loses its water of crystallisation in dry air or on gentle heating and becomes slightly deliquescent in moist air; the anhydrous form is hygroscopic. Dilute aqueous solutions may ferment on standing. Store in an airtight container in a cool, dry place.

Incompatible with potassium tartrate, alkali and alkaline-earth carbonates and bicarbonates, acetates and sulfides, and with oxidising agents, bases, reducing agents and nitrates; mixtures with metal nitrates are potentially explosive. Its acidity can catalyse hydrolysis of acid-labile drugs, and in effervescent blends moisture triggers premature reaction with carbonates.

Produced mainly by fermentation of carbohydrates such as molasses, sucrose or glucose with strains of Aspergillus niger. The acid is recovered, for example by precipitation as calcium citrate followed by treatment with sulfuric acid, or by solvent extraction, then purified and crystallised either as the monohydrate (below about 36 °C) or as the anhydrous form.

Citric acid is a normal metabolite and is widely used in foods and medicines; it is generally regarded as non-toxic at the levels used. Frequent or prolonged contact with the teeth can erode dental enamel, and concentrated solutions or the powder irritate the skin, eyes and mucous membranes. JECFA has not set a limit on its acceptable daily intake.

Observe normal precautions for the quantity handled. The powder irritates the eyes and respiratory tract; wear eye protection and gloves and avoid generating dust.

GRAS listed. Accepted as a food additive in Europe (E330). Included in the FDA Inactive Ingredient Database (inhalation, injections, oral, nasal, ophthalmic, rectal, topical and vaginal preparations) and in parenteral and non-parenteral medicines licensed in Europe.

Sodium citrate; potassium citrate; calcium citrate; fumaric acid; malic acid; tartaric acid.

Choose the anhydrous form for moisture-sensitive products such as effervescent tablets, which are made under low humidity; the monohydrate is common in liquids. Citrate buffers are effective roughly between pH 3 and 6.2. Correct for water content when substituting one form for the other (192.12 g anhydrous ≡ 210.14 g monohydrate).