CALCIUM ALGINATE

Prepared at the 17th JECFA (1973), published in FNP 4 (1978) and in FNP 52 (1992)

SYNONYMS

INS No. 404

DEFINITION

Calcium Alginate, the calcium salt of alginic acid, is a colloidal substance. The alginic acid is a linear high-polymer consisting mainly of ß-(1→4) linked D-mannuronic acid in the pyranose ring form, with part of the mannuronic acid replaced by L-guluronic acid.

C.A.S. number

9005-35-0

Chemical formula

(C₆ H₇ Ca_1/2 O₆)_n

Structural formula

Formula weight

Structural unit: 195.16 (theoretical), 219 (actual average)

Macromolecule: 32,000 - 250,000

Assay

Not less than 18.0% and not more than 21.0% of carbon dioxide (CO₂), equivalent to not less than 89.6% and not more than 104.5% of calcium alginate (C₆H₇Ca_1/2 O₆)_n.

DESCRIPTION

White to yellowish brown filamentous, grainy, granular and powdered forms

FUNCTIONAL USES

Stabilizer and thickener.

CHARACTERISTICS

IDENTIFICATION

Solubility

Insoluble in water and ether; slightly soluble in ethanol; slowly soluble in solutions of sodium polyphosphate, sodium carbonate, and substances that combine with the calcium.

Specific rotation

Clarify a 0.5% solution of the sample in sodium hydroxide TS with kieselguhr, and determine the rotation in a 20-cm tube. The specific rotation is not less than -0.8o at 20o.

Precipitate formation with calcium chloride

To a 0.5% solution of the sample in sodium hydroxide TS add one-fifth of its volume of a 2.5% solution of calcium chloride. A voluminous, gelatinous precipitate is formed. This test distinguishes ammonium alginate from gum arabic, sodium carboxymethyl cellulose, carrageenan, gelatin, gum ghatti, karaya gum, carob bean gum, methyl cellulose and tragacanth gum.

Precipitate formation with ammonium sulfate

To a 0.5% solution of the sample in sodium hydroxide TS add one-half of its volume of a saturated solution of ammonium sulfate. No precipitate is formed. This test distinguishes ammonium alginate from agar, sodium carboxymethyl cellulose, carrageenan, de-esterified pectin, gelatin, carob bean gum, methyl cellulose and starch.

Colour reaction

Passes test

Moisten 1-5 mg of the sample with water, and add 1 ml of acid ferric sulfate TS. Within 5 min, a cherry-red colour develops that finally becomes deep purple.

Test for calcium

Passes test

Dissolve the sulfated ash of the sample in dilute acetic acid TS and filter. Treat the filtrate with ammonium oxalate TS. The white precipitate formed is soluble in hydrochloric acid.

PURITY

Loss on drying

Not more than 15% (105^o, 4 h)

Phosphate

Not detectable

To an 0.5% aqueous solution of the sample add one-fifth of its volume of 4 N nitric acid and 1 volume of ammonium molybdate TS and warm. No yellow precipitate should be formed.

Total ash

Not less than 13% and not more than 24% on the dried basis

Arsenic

Not more than 3 % mg/kg (Method II)

Lead

Not more than 10 mg/kg

Prepare a sample solution as directed for organic compounds in the Limit Test, using 10 µg of lead ion (Pb) in the control

Heavy metals

Not more than 40 mg/kg

Test 0.5 g of the sample as directed under the Limit Test (Method II)

METHOD OF ASSAY

Decarboxylation method

Proceed as directed under Carbon Dioxide Determination by Decarboxylation in the General Methods. Each ml of 0.25 N sodium hydroxide consumed is equivalent to 5.5 mg of carbon dioxde (CO2) or 27.38 mg of calcium alginate (equivalent weight 219.00).

Gravimetric method

Dissolve 0.500 g of the sample in 10 ml of sodium hydroxide TS, add 90 ml of water, and filter if necessary. Add 15 ml of 4 N hydrochloric acid and 100 ml of 90% v/v ethanol. Allow this mixture to stand for 2 h, decant the supernatant liquid as far as possible, and centrifuge. Decant the liquid and replace it by 90% v/v ethanol. Mix well, centrifuge and decant again. This washing is repeated until the hydrochloric acid is removed. Then transfer the precipitate by mean of 90% v/v ethanol to a fine glass filter, wash with dry acetone, place the filter in a vacuum desiccator, and dry to constant weight at 100o.

Calculate the percent purity of the sample by the formula:

% Purity = (200 x F x W ) / % dry substance in sample x 100

in which F is a conversion factor specified as 1.108 and W is the weight (in grams) of the dried precipitate.