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SODIUM SULFITE

 

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

Disodium sulfite, INS No. 221

DEFINITION

 

Chemical names

Sodium sulfite

C.A.S. number

7757-83-7

Chemical formula

Na2SO3

Formula weight

126.04

Assay

Not less than 95.0%

DESCRIPTION

White powder with not more than a faint odour of sulfur dioxide

FUNCTIONAL USES

Antibrowning agent, antioxidant, preservative

CHARACTERISTICS

 

IDENTIFICATION

 

Solubility (FNP 5)

Freely soluble in water; sparingly soluble in ethanol

Test for sodium (FNP 5)

Passes test

Test for sulfite (FNP 5)

Passes test

PURITY

 

pH (FNP 5)

8.5 - 10.0 (1 in 10 soln)

Thiosulfate

Not more than 0.1%
A 10% solution of the sample should remain clear on acidification with sulfuric or hydrochloric acid.

Iron (FNP 5)

Not more than 10 mg/kg
Proceed as directed in the Limit Test using 0.5 ml of Iron Standard Solution (5 g Fe) in the control

Lead (FNP 5)

Not more than 2 mg/kg
Determine by atomic absorption spectroscopy (FNP 5)

Selenium

Not more than 5 mg/kg
See description under TESTS

TESTS

 

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.
Into a second beaker, weigh 1.0 0.1 g of sample, add 0.05 ml standard selenium solution and proceed as above.
To each beaker add 2 g hydrazinium sulfate and warm to dissolve. Let stand for 5 min. Dilute the contents of each beaker to 50 ml in a Nessler tube and compare the colour of the two solutions. The sample should be less pink than the sample with the added standard.

METHOD OF ASSAY

Weigh 250 mg of the sample, add to 50.0 ml of 0.1 N iodine in a glass-stoppered flask, and stopper the flask. Allow to stand for 5 min, add 1 ml of hydrochloric acid and titrate the excess iodine with 0.1 N sodium thiosulfate, adding starch TS as the indicator. Each ml of 0.1 N iodine is equivalent to 6.302 mg of Na2SO3.

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