Alginic Acid

Alginic Acid

Alginic acid is a tasteless, practically odorless, and white to yellowishwhite, fibrous powder
Related SubstancesAmmonium alginate; calcium alginate; potassium alginate; propylene glycol alginate; sodium alginate.
Nonproprietary Names

  • BP: Alginic Acid
  • PhEur: Alginic Acid
  • USP-NF: Alginic Acid


Acidum alginicum; E400; Kelacid; L-gulo-D-mannoglycuronan; polymannuronic acid; Protacid; Satialgine H8.
Chemical Name and CAS Registry Number: Alginic acid [9005-32-7]
Empirical Formula and Molecular Weight: Alginic acid is a linear glycuronan polymer consisting of a mixture of b-(1!4)-D-mannosyluronic acid and a-(1!4)-L-gulosyluronic acid residues, of general formula (C6H8O)n. 
The molecular weight is typically 20 000–240 000.

Structural Formula

The PhEur 6.3 describes alginic acid as a mixture of polyuronic acids [(C6H8O6) n] composed of residues of D-mannuronic and Lglucuronic acid, and obtained mainly from algae belonging to the Phaeophyceae. A small proportion of the carboxyl groups may be neutralized.

Functional Category

Release-modifying agent; stabilizing agent; suspending agent; sustained release agent; tablet binder; tablet disintegrant; taste masking agent; viscosity-increasing agent.

Applications in Pharmaceutical Formulation or Technology

Alginic acid is used in a variety of oral and topical pharmaceutical formulations. In tablet and capsule formulations, alginic acid is used as both a binder and disintegrating agent at concentrations of 1–5% w/w. Alginic acid is widely used as a thickening and suspending agent in a variety of pastes, creams, and gels; and as a stabilizing agent for oil-in-water emulsions. 

Alginic acid has been used to improve the stability of levosimendan. Therapeutically, alginic acid has been used as an antacid. In combination with an H2-receptor antagonist, it has also been utilized for the management of gastroesophageal reflux.

Typical Properties

  • Acidity/alkalinity: pH = 1.5–3.5 for a 3% w/v aqueous dispersion.
  • Crosslinking: Addition of a calcium salt, such as calcium citrate or calcium chloride, causes crosslinking of the alginic acid polymer resulting in an apparent increase in molecular weight. Films crosslinked with triphosphate (tripolyphosphate) and calcium chloride were found to be insoluble but permeable to water vapor. Drug permeability varies with pH and the extent of crosslinking
  • Density (true) 1.601 g/cm3
  • Moisture content 7.01%
  • Solubility:  Soluble in alkali hydroxides, producing viscous solutions; very slightly soluble or practically insoluble in ethanol (95%) and other organic solvents. Alginic acid swells in water but does not dissolve; it is capable of absorbing 200–300 times its own weight of water.
  • Viscosity (dynamic):  Various grades of alginic acid are commercially available that vary in their molecular weight and hence viscosity. Viscosity increases considerably with increasing concentration; typically a 0.5% w/w aqueous dispersion will have a viscosity of approximately 20 mPa s, while a 2.0% w/w aqueous dispersion will have a viscosity of approximately 2000 mPa s. The viscosity of dispersions decreases with increasing temperature. As a general rule, a 18C increase in temperature results in a 2.5% reduction in viscosity. At low concentrations, the viscosity of an alginic acid dispersion may be increased by the addition of a calcium salt, such as calcium citrate.

Method of Manufacture
Alginic acid is a hydrophilic colloid carbohydrate that occurs naturally in the cell walls and intercellular spaces of various species of brown seaweed (Phaeophyceae). The seaweed occurs widely throughout the world and is harvested, crushed, and treated with dilute alkali to extract the alginic acid.



Leave a Reply

%d bloggers like this: