E 466 SODIUM CARBOXY METHYL CELLULOSE

Commission Directive 98/86/EC

Synonyms Carboxy methyl cellulose

CMC
NaCMC
Sodium CMC
Cellulose gum

Definition Carboxy methyl cellulose is the partial sodium salt of a carboxymethyl ether of cellulose, the cellulose being obtained directly from natural strains of fibrous plant material

Chemical name Sodium salt of the carboxymethyl ether of cellulose

Chemical formula The polymers contain substituted anhydroglucose units with the following general formula: C₆H₇O₂(OR₁)(OR₂)(OR₃), where R₁, R₂ R₃ each may be one of the following:

- H

- CH₂COONa

- CH₂COOH

Molecular weight Higher than approximately 17 000 (degree of polymerisation approximately 100)

Assay Content on the anhydrous basis not less than 99,5 %

Description Slightly hygroscopic white or slightly yellowish or greyish odourless and tasteless, granular or fibrous powder

Identification

A. Solubility Yields a viscous colloidal solution with water. Insoluble in ethanol

B. Foam test A 0,1 % solution of the sample is shaken vigorously. No layer of foam appears. (This test permits the distinction of sodium carboxymethyl cellulose from other cellulose ethers)

C. Precipitate formation To 5 ml of a 0,5 % solution of the sample, add 5 ml of 5 % solution of copper sulphate or of aluminium sulphate. A precipitate appears. (This test permits the distinction of sodium carboxymethyl cellulose from other cellulose ethers and from gelatine, locust bean gum and tragacanth)

D. Colour reaction Add 0,5 g powdered carboxy methyl cellulose sodium to 50 ml of water, while stirring to produce an uniform dispersion. Continue the stirring until a clear solution is produced, and use the solution for the following test:

To 1 mg of the sample, diluted with an equal volume of water, in a small test tube, add 5 drops of 1-naphthol solution. Incline the test tube, and carefully introduce down the side of the tube 2 ml of sulphuric acid so that it forms a lower layer. A red-purple colour develops at the interface

Purity

Degree of substitution Not less than 0,2 and not more than 1,5 carboxymethyl groups (-CH₂COOH) per anhydroglucose unit

Loss on drying Not more than 12 % (105 °C to constant weight)

pH of a 1 % colloidal solution Not less than 5,0 and not more than 8,5

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 glycolate Not more than 0,4 %, calculated as sodium glycolate on the anhydrous basis

Sodium Not more than 12,4 % on the anhydrous basis