SODIUM THIOSULFATE

Prepared at the 51st JECFA (1998), published in FNP 52 Add 6 (1998) superseding specifications prepared at the 22nd JECFA (1978), published in FNP 7 (1978) and republished in FNP 52 (1992). Group ADI 0-0.7 mg/kg bw as SO2 for sulfites, established at the 51st JECFA in 1998.

The existing specifications were revised and designated tentative. Information on iron and selenium levels in commercial products and on the test method for selenium is required by 30 March 1999. The existing specifications include a selenium limit for which the test method is no longer feasible because of lack of availability of required reagents. The Committee also questioned the need for selenium limit because new processes in sulfur production as a by-product of the oil industry have replaced extraction methods from sulfur mines. The Committee noted that the selenium limit may no longer be necessary and requested information in this regard.

SYNONYMS

Sodium hyposulfite; INS No. 539

DEFINITION

Chemical names

Sodium thiosulfate

C.A.S. number

7772-98-7

Chemical formula

Na₂S₂O₃ · 5H₂O

Formula weight

248.17

Assay

Not less than 99.0% and not more than 100.5 of Na₂S₂O₃ on the dried basis

DESCRIPTION

Colourless crystals or coarse crystalline powder; deliquesces in moist air and effloresces in dry air above 33^o

FUNCTIONAL USES

Antibrowning agent, antioxidant, sequestrant

CHARACTERISTICS

IDENTIFICATION

Solubility

Very soluble in water; insoluble in ethanol

Reducing activity

To a 1 in 10 solution of the sample add a few drops of iodine TS; the colour is discharged

Test for sodium

Passes test

Test for thiosulfate

Passes test

PURITY

Loss on drying

32-37% (40-45^o, 16 h, under vacuum)

Lead

Not more than 2 mg/kg

Determine by atomic absorption spectroscopy

METHOD OF ASSAY

Dissolve about 0.5 g of the dried sample, accurately weighed, in 30 ml of water and titrate with 0.1 N iodine solution using starch TS as the indicator. Each ml of 0.1 N iodine is equivalent to 15.81 mg of Na₂S₂O₃.

Prepared at the 51st JECFA (1998), published in FNP Add. 6 (1998) superseding specifications prepared at the 44th JEFCA (1995), published in FNP 52 Add 3 (1995). Group ADI 0-25 mg/kg bw for sorbitan esters of lauric, oleic, palmitic and stearic acids, established at the 26th JECFA in 1982).

SYNONYMS

INS No. 493

DEFINITION

A mixture of the partial esters of sorbitol and its mono- and dianhydrides with edible lauric acid

C.A.S. number

1338-39-2

Structural formula

Contains lauric acid esterified with polyols derived from sorbitol including the following types:

Assay

Saponification of 100 g of the sample yields not less than 36 g and not more than 49 g of polyols, and not less than 56 g and not more than 68 g of fatty acids. The polyol content shall be not less than 95% of a mixture of sorbitol, 1,4-sorbitan and isosorbide.

DESCRIPTION

Amber-coloured oily viscous liquid, light cream to tan beads or flakes or a hard, waxy solid with a slight odour

FUNCTIONAL USES

Emulsifier, stabilizer

CHARACTERISTICS

IDENTIFICATION

Solubility

Dispersible in hot and cold water

PURITY

Water

Not more than 2% (Karl Fischer Method)

Sulfated ash

Not more than 0.5%

Acid value

Not more than 7

Saponification value

Not less than 155 and not more than 170

Hydroxyl value

Not less than 330 and not more than 358

Lead

Not more than 2 mg/kg

Prepare the sample as directed for organic compounds in the Limit Test and determine by atomic absorption spectrosocopy

METHOD OF ASSAY

Transfer about 25 g of the sample, accurately weighed, into a 500-ml round-bottom flask, add 250 ml of alcohol and 7.5 g of potassium hydroxide, and mix. Connect a suitable condenser to the flask, reflux the mixture for 1 to 2 h, and then transfer to an 800-ml beaker, rinsing the flask with about 100 ml of water and adding it to the beaker. Heat on a steam bath to evaporate the alcohol, adding water occasionally to replace the alcohol, and evaporate until the odor of alcohol can no longer be detected. Adjust the final volume to about 250 ml with hot water. Neutralize the soap solution with dilute sulfuric acid (1 in 2), add 10% in excess, and heat, while stirring, until the fatty acid layer separates. Transfer the fatty acids to a 500-ml separator, wash with three or four 20-ml portions of hot water to remove polyols, and combine the washings with the original aqueous polyol layer from the saponification. Extract the combined aqueous layer with three 20-ml portions of petroleum ether, add the extracts to the fatty acid layer, evaporate to dryness in a tared dish, cool and weigh.

Neutralize the polyol solution with a 1 in 10 solution of potassium hydroxide to pH 7 using a suitable pH meter. Evaporate this solution to a moist residue, and separate the polyols from the salts by several extractions with hot alcohol. Evaporate the alcohol extracts on a steam bath to dryness in a tared dish, cool, and weigh. Avoid excessive drying and heating.