Molecular formula. NaF

Relative molecular mass. 41.99

Chemical name. Sodium fluoride; CAS Reg. No. 7681-49-4.

Description. A white powder; odourless.

Solubility. Soluble in water; practically insoluble in ethanol (~750 g/l) TS.

Category. Mineral salt.

Storage. Sodium fluoride should be kept in a well-closed container.

Requirements

Definition. Sodium fluoride contains not less than 98.0% and not more than 101.0% of NaF, 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 20 mg/mL solution.

B. Place 0.10 g in a lead or platinum crucible, add about 1 mL of sulfuric acid (~1760 g/l) TS, cover the crucible with a piece of clear polished glass, and heat on a water-bath for 15 minutes. Remove the glass cover, rinse with water and wipe dry; the surface of the glass is etched.

C. Add a few mg of the test substance to a mixture of 0.10 mL of freshly prepared sodium alizarinsulfonate (10 g/l) TS and 0.10 mL of zirconyl nitrate TS; a red colour develops, which changes to yellow.

Heavy metals. Use 0.5 g for the preparation of the test solution as described under 2.2.3 Limit test for heavy metals, Procedure 3; determine the heavy metals content according to Method A; not more than 40 μg/g.

Loss on drying. Dry to constant weight at 130°C; it loses not more than 10 mg/g.

Acidity or alkalinity. Dissolve 1.0 g in 20 mL of water in a platinum dish, add and dissolve into this solution 3 g of potassium nitrate R, and cool to 0°C. Add 0.15 mL of phenolphthalein/ethanol TS; not more than 2.0 mL of sodium hydroxide (0.05 mol/l) VS or 1.0 mL of sulfuric acid (0.05 mol/l) VS is required to obtain the midpoint of the indicator (pink). (Keep the solution for the test of fluorosilicates.)

Fluorosilicates. Heat to boiling the solution obtained in the test for acidity or alkalinity and titrate while hot with sodium hydroxide (0.05 mol/l) VS until a permanent pink colour is produced; not more than 1.5 mL of sodium hydroxide (0.05 mol/l) VS are required.

Assay. Dissolve about 30 mg, accurately weighed, in 1.0 mL of water. Add cautiously 15 mL of acetic anhydride R and boil gently for 2 minutes, placing a small funnel on the flask to serve as a reflux condenser. Cool and titrate with perchloric acid (0.1 mol/l) VS as described under 2.6 Non-aqueous titration, Method A. Each mL of perchloric acid (0.1 mol/l) VS is equivalent to 4.199 mg of NaF.