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POTASSIUM 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

INS No. 225

DEFINITION

 

Chemical names

Potassium sulfite

C.A.S. number

10117-38-1

Chemical formula

K2SO3

Formula weight

158.25

Assay

Not less than 90.0%

DESCRIPTION

White, odourless, granular powder

FUNCTIONAL USES

Antibrowning agent, antioxidant, preservative

CHARACTERISTICS

 

IDENTIFICATION

 

Solubility (FNP 5)

Freely soluble in water; slightly soluble in ethanol

Test for potassium (FNP 5)

Passes test

Test for sulfite (FNP 5)

Passes test

PURITY

 

Alkalinity

Between 0.25 and 0.45% as K2CO3
Dissolve 1 g of the sample in 20 ml of water and add 25 ml of 3% hydrogen peroxide, previously neutralized to methyl red TS. Mix thoroughly, cool to room temperature, and titrate with 0.02 N hydrochloric acid. Perform a blank determination using 25 ml of neutralized hydrogen peroxide solution. Each ml of 0.02 N hydrochloric acid is equivalent to 1.38 mg of K2CO3.

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 spectrometry (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 accurately about 0.75 g of the sample and dissolve in a mixture of 100 ml of 0.1 N iodine and 5 ml of dilute hydrochloric acid TS. 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 7.912 mg of K2SO3.

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