Prepared at the 53rd JECFA (1999) and published in FNP 52 Add 7 (1999), superseding tentative specifications prepared at the 51st JECFA (1998), published in FNP 52 Add 6 (1998). Group ADI 0-0.7 mg/kg bw as SO2 for sulfites established at the 51st JECFA in 1998. | |
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% on the dried basis |
DESCRIPTION |
Colourless crystals or coarse crystalline powder; deliquesces in moist air and effloresces in dry air above 33� |
FUNCTIONAL USES |
Antibrowning agent, antioxidant, sequestrant |
CHARACTERISTICS |
|
IDENTIFICATION |
|
Solubility (FNP 5) |
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 (FNP 5) |
Passes test |
Test for thiosulfate (FNP 5) |
Passes test |
PURITY |
|
Loss on drying (FNP 5) |
32-37% (40-45�, 16 h, under vacuum) |
Lead (FNP 5) |
Not more than 2 mg/kg |
Iron (FNP 5) |
Not more than 10 mg/kg |
Selenium |
Not more than 5 mg/kg |
TESTS |
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PURITY TESTS |
|
Selenium |
Reagents: Hydrochloric acid, hydrazinium sulfate, standard selenium solution (100 �g Se/ml) Procedure Weigh 2.0 � 0.1 g of sample and transfer to a 50-ml beaker. Add 10 ml water, 5 ml hydrochloric acid and boil to remove SO2. |
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. |