Packaging and storage—
Preserve in well-closed containers.
Identification—
A:
Place 1 g in a platinum crucible in a well-ventilated hood, add 15 mL of sulfuric acid, and cover the crucible with a piece of clear, polished glass. Heat the crucible on a steam bath for 1 hour, remove the glass cover, rinse it in water, and wipe dry: the surface of the glass is etched.
B:
A solution (1 in 25) responds to the tests for
Sodium 
191
.
Acidity or alkalinity—
Dissolve 2.0 g in 40 mL of water in a platinum dish, add 10 mL of a saturated solution of potassium nitrate, cool the solution to 0
, and add 3 drops of phenolphthalein TS. If no color appears, a pink color persisting for 15 seconds is produced by not more than 2.0 mL of 0.10 N sodium hydroxide. If the solution is colored pink by the addition of
phenolphthalein TS, it is rendered colorless by not more than 0.50 mL of 0.10 N sulfuric acid. Save the neutralized solution for the test for
Fluosilicate.
Fluosilicate—
After the solution from the test for
Acidity or alkalinity has been neutralized, heat to boiling, and titrate while hot with 0.10 N sodium hydroxide until a permanent pink color is obtained: not more than 1.5 mL of 0.10 N sodium hydroxide is required.
Chloride—
Dissolve 300 mg in 20 mL of water, and add 200 mg of boric acid, 1 mL of nitric acid, and 1 mL of 0.1 N silver nitrate: any turbidity produced is not greater than that of a blank to which has been added 1.0 mL of 0.0010 N hydrochloric acid (0.012%).
Heavy metals 231—
To 1 g, in a platinum dish or crucible, under a hood, add 1 mL of water and 3 mL of sulfuric acid, and heat at as low a temperature as practicable until all of the sulfuric acid has been expelled. Dissolve the residue in 20 mL of water, neutralize the solution to
phenolphthalein TS with ammonium hydroxide, add 1 mL of glacial acetic acid, dilute with water to 45 mL, filter, and use 30 mL of the filtrate for the test: the limit is 0.003%.
Organic volatile impurities, Method I 467:
meets the requirements.
Assay—
[NOTE—Store all solutions, except the
Buffer solution, in plastic containers.
]
Assay preparation—
Transfer about 100 mg of Sodium Fluoride, accurately weighed, to a 250-mL volumetric flask. Add 50 mL of water, mix for 5 minutes, dilute with water to volume, and mix. Transfer 10.0 mL of this solution to a 50-mL volumetric flask, dilute with water to volume, and mix.
Procedure—
Proceed as directed for
Procedure in the
Assay under
Sodium Fluoride Oral Solution. Calculate the quantity, in mg, of NaF in the portion of Sodium Fluoride taken by the formula:
(41.99 / 18.998)(1.25C),
in which 41.99 is the molecular weight of sodium fluoride; 18.998 is the atomic weight of fluorine; and
C is the determined concentration of fluoride, in µg per mL, in the
Assay preparation.
