| 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 | |
A.Solubility | Insoluble in water and organic solvents, slowly soluble in solutions of sodium carbonate, sodium hydroxide and trisodium phosphate |
B.Calcium chloride precipitation test | 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 |
C.Ammonium sulphate precipitation test | 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 |
D.Colour reaction | 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 |
