Definition

Linear glycuronoglycan consisting mainly of β-(1-4) linked D-mannuronic and α-(1-4) linked L-guluronic acid units in pyranose ring form. Hydrophilic colloidal carbohydrate extracted by the use of dilute alkali from natural strains of various species of brown seaweeds (Phaeophyceae)

Einecs

232-680-1

Chemical formula

(C₆H₈O₆)_n

Molecular weight

10 000-600 000 (typical average)

Assay

Alginic acid yields, on the anhydrous basis, not less than 20 % and not more than 23 % of carbon dioxide (CO₂), equivalent to not less than 91 % and not more than 104,5 % of alginic acid (C₆H₈O₆)_n (calculted on equivalent weight basis of 200)

Description

Alginic acid occurs in filamentous, grainy, granular and powdered forms. It is a white to yellowish brown and nearly odourless

Identification

Insoluble in water and organic solvents, slowly soluble in solutions of sodium carbonate, sodium hydroxide and trisodium phosphate

To a 0,5 % solution of the sample in 1 M sodium hydroxide solution, add one fifth of its volume of a 2,5 % solution of calcium chloride. A voluminous, gelatinous precipitate is formed. This test distinguishes alginic acid from acacia gum, sodium carboxymethyl cellulose, carboxymethyl starch, carrageenan, gelatin, gum ghatti, karaya gum, locust bean gum, methyl cellulose and tragacanth gum

To a 0,5 % solution of the sample in 1 M sodium hydroxide solution, add one half of its volume of a saturated solution of ammonium sulphate. No precipitate is formed. This test distinguishes alginic acid from agar, sodium carboxymethyl cellulose, carrageenan, de-esterified pectin, gelatin, locust bean gum, methyl cellulose and starch

Dissolve as completely as possible 0,01 g of the sample by shaking with 0,15 ml of 0,1 N sodium hydroxide and add 1 ml of acid ferric sulphate solution. Within 5 minutes, a cherry-red colour develops that finally becomes deep purple

Purity

pH of a 3 % suspension

Between 2,0 and 3,5

Loss on drying

Not more than 15 % (105 ^oC, 4 hours)

Sulphated ash

Not more than 8 % on the anhydrous basis

Sodium hydroxide (1 M solution)

Not more than 2 % on the anhydrous basis insoluble matter

Arsenic

Not more than 3 mg/kg

Lead

Not more than 5 mg/kg

Mercury

Not more than 1 mg/kg

Cadmium

Not more than 1 mg/kg

Heavy metals (as Pb)

Not more than 20 mg/kg

Total plate count

Not more than 5 000 colonies per gram

Yeast and moulds

Not more than 500 colonies per gram

E. coli

Negative in 5 g

Salmonella spp.

Negative in 10 g