Sodium Fluoride
(soe' dee um floor' ide).

NaF 41.99
Sodium fluoride     [7681-49-4].
DEFINITION
Sodium Fluoride contains NLT 98.0% and NMT 102.0% of NaF, calculated on the dried basis.
IDENTIFICATION
•  A. Fluoride
Sample:  1 g
Analysis:  Place the Sample 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 h, remove the glass cover, rinse it in water, and wipe dry.
Acceptance criteria:  The surface of the glass is etched.
•  B. Identification Tests—General, Sodium 191
Sample solution:  1 in 25
Acceptance criteria:  Meets the requirements
ASSAY
•  Procedure
Sample solution:  To 80.0 mg add a mixture of 5 mL of acetic anhydride and 20 mL of glacial acetic acid, and heat to dissolve. Allow to cool. [Note—The heating step to dissolve the sodium fluoride in the acetic acid mixture is critical. It is recommended to heat for a minimum of 30 min and use sonication, if necessary, to make sure dissolution is complete prior to the titration step. ]
Analysis:  Add 20 mL of dioxane to the Sample solution. Add 1 drop of crystal violet TS, and titrate with 0.1 N perchloric acid VS to a green endpoint. Perform a blank determination, and make any necessary correction (see Titrimetry 541). Each mL of 0.1 N perchloric acid is equivalent to 4.199 mg of NaF.
Acceptance criteria:  98.0%–102.0% on the dried basis
IMPURITIES
•  Chloride
Sample solution:  300 mg in 20 mL of water
Analysis:  To the Sample solution add 200 mg of boric acid, 1 mL of nitric acid, and 1 mL of 0.1 N silver nitrate.
Acceptance criteria:  Any turbidity produced is NMT that of a blank to which has been added 1.0 mL of 0.0010 N hydrochloric acid (NMT 0.012%).
•  Heavy Metals 231
Test preparation:  Place 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, and neutralize the solution to phenolphthalein TS with ammonium hydroxide. Add 1 mL of glacial acetic acid, dilute with water to 45 mL, and filter. Use 30 mL of the filtrate for the test.
Acceptance criteria:  NMT 30 ppm
SPECIFIC TESTS
•  Acidity or Alkalinity
Sample:  2.0 g
Analysis:  Dissolve the Sample 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.
Acceptance criteria:  If no color appears, a pink color persisting for 15 s is produced by NMT 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 NMT 0.50 mL of 0.10 N sulfuric acid. [Note—Save the neutralized solution for the test for Fluosilicate. ]
•  Loss on Drying 731: Dry a sample at 150 for 4 h: it loses NMT 1.0% of its weight.
•  Fluosilicate
Analysis:  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.
Acceptance criteria:  NMT 1.5 mL of 0.10 N sodium hydroxide is required.
ADDITIONAL REQUIREMENTS
•  Packaging and Storage: Preserve in well-closed containers.
Auxiliary Information— Please check for your question in the FAQs before contacting USP.
Topic/Question Contact Expert Committee
Monograph Elena Gonikberg, Ph.D.
Principal Scientific Liaison
1-301-816-8251
(SM32010) Monographs - Small Molecules 3
USP35–NF30 Page 4658
Pharmacopeial Forum: Volume No. 34(3) Page 653