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SODIUM METABISULFITE

 

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 sulfite established at the 51st JECFA in 1998.

SYNONYMS

INS No. 223

DEFINITION

 

Chemical names

Sodium disulfite, disodium pentaoxodisulfate, disodium pyrosulfite

C.A.S. number

7681-57-4

Chemical formula

Na2S2O5

Formula weight

190.11

Assay

Not less than 90.0%

DESCRIPTION

White crystals or crystalline powder having an odour of sulfur dioxide

FUNCTIONAL USES

Antibrowning agent, antioxidant, flour treatment agent, preservative

CHARACTERISTICS

 

IDENTIFICATION

 

Solubility (FNP 5)

Freely soluble in water; slightly soluble in ethanol

Test for sodium (FNP 5)

Passes test

Test for sulfite (FNP 5)

Passes test

PURITY

 

Water insolubles

Dissolve 20 g of the sample in 200 ml of water. The solution should be clear with only a trace of suspended matter

pH (FNP 5)

4.0 - 4.5 (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 (100g 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 0.2 g of the sample to the nearest mg, 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 4.753 mg of Na2S2O5.

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