Molecular formula. NaNO₂

Relative molecular mass. 69.00

Chemical name. Nitrous acid, sodium salt; CAS Reg. No. 7632-00-0.

Description. A white to slightly yellow, granular powder, or white or almost white, opaque, fused masses or sticks; odourless.

Solubility. Freely soluble in water; sparingly soluble in ethanol (~750 g/l) TS.

Category. Vasodilator.

Storage. Sodium nitrite should be kept in a well-closed container, protected from light.

Additional information. Sodium nitrite is deliquescent in air. Even in the absence of light, it is gradually degraded on exposure to a humid atmosphere, the decomposition being faster at higher temperatures.

Requirements

Definition. Sodium nitrite contains not less than 98.0% and not more than 100.5% of NaNO₂, calculated with reference to the dried substance.

Identity tests

A. When tested for sodium as described under 2.1 General identification tests yields the characteristic reactions. If reaction B is to be used, prepare a 0.10 g/mL solution acidified with acetic acid (~300 g/l) TS.

B. Dissolve 0.10 g in 1.0 mL of water and add 1.0 mL of ferrous sulfate(~15 g/l) TS; after a few minutes a deep brown colour is produced.

C. Dissolve 0.20 g in 1.0 mL of water and add 1.0 mL of sulfuric acid (~100 g/l) TS; brownish red fumes are evolved. Add a few drops of starch/iodide TS; a blue colour is produced.

Heavy metals. Dissolve 1.0 g in 10 mL of hydrochloric acid (~70 g/l) TS, evaporate to dryness on a water-bath and until the odour of hydrochloric acid is no longer perceptible. Proceed with the residue as described under 2.2.3 Limit test for heavy metals, Procedure 1; determine the heavy metals content according to Method A; not more than 20 μg/g.

Chlorides. For the preparation of the test solution, boil 2.5 g in a mixture of 3 mL of water and 2 mL of nitric acid (~1000 g/l) TS, cool, and proceed as described under 2.2.1 Limit test for chlorides; the chloride content is not more than 0.1 mg/g.

Loss on drying. Dry at ambient temperature over silica gel, desiccant, R for 4 hours; it loses not more than 5.0 mg/g.

Acidity or alkalinity. To a solution of 0.5 g in 10 mL of water add 0.1 mL of sodium hydroxide (0.01 mol/l) VS and 0.25 mL of phenol red/ethanol TS; a red colour is produced. Add 0.3 mL of hydrochloric acid (0.01 mol/l) VS; the colour changes to yellow.

Assay. Dissolve about 0.4 g, accurately weighed, in sufficient water to produce 100 mL. To 10.0 mL of this solution add 20.0 mL of potassium permanganate (0.02 mol/l) VS and 10 mL of sulfuric acid (~1760 g/l) TS. Allow to stand for 10 minutes, add 0.5 g of potassium iodide R, swirl the flask, and titrate the liberated iodine with sodium thiosulfate (0.1 mol/l) VS, using starch TS as indicator. Each mL of sodium thiosulfate (0.1 mol/l) VS is equivalent to 3.450 mg of NaNO₂.

Additional requirements for Sodium nitrite for parenteral use

Complies with the monograph for "Parenteral preparations".

Bacterial endotoxins. Carry out the test as described under 3.4 Test for bacterial endotoxins; contains not more than 0.33 IU of endotoxin RS per mg.