Sodium Fluoride

This article is compiled based on the United States Pharmacopeia (USP) – 2025 Edition

Issued and maintained by the United States Pharmacopeial Convention (USP)

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NaF 41.99

Sodium fluoride CAS RN

®: 7681-49-4; UNII: 8ZYQ1474W7.

1 DEFINITION

Sodium Flfluoride contains NLT 98.0% and NMT 102.0% of sodium fluoride (NaF), calculated on the dried basis.

2 IDENTIFICATION

Change to read:

A. Flfluoride: The retention time of the fluoride peak of the Sample solution corresponds to that of the Standard solution, as obtained in the Assay. (USP 1-Aug-2021)

Change to read:

B. Identification Tests—General 〈191〉, Chemical Identification Tests, Sodium

Sample solution: 40 mg/mL in water (USP 1-Aug-2021)

Acceptance criteria: Meets the requirements

3 ASSAY

Change to read:

3.1 Procedure

[Note—Store all solutions in plastic containers. It is recommended to use plastic HPLC vials. Use water with a resistivity of NLT 18 megohm- cm to prepare the solutions.]

Mobile phase: 15 mM potassium hydroxide in water. [Note—Mobile phase can be generated electrolytically using an automatic eluant generator.]

System suitability solution: 2.0 μg/mL of USP Sodium Flfluoride RS and 1.0 μg/mL of USP Sodium Acetate RS in water

Standard solution: 2.0 μg/mL of USP Sodium Flfluoride RS in water

Sample solution: 2.0 μg/mL of Sodium Flfluoride in water

3.2 Chromatographic system

(See Chromatography 〈621〉, System Suitability.)

Mode: LC

Detector: Conductivity with suppression

Columns

Guard: 4.0-mm × 5-cm; 13-μm packing L120. [Note—Alternatively, a 4.0-mm × 0.5-cm column that contains 4.6-μm packing L91 may be used.]

Analytical: 4.0-mm × 25-cm; 7.5-μm packing L113. [Note—Alternatively, a 4.0-mm × 25-cm column that contains 4.6-μm packing L91 may be used.]

Column temperature: 40°

Flow rate: 1.0 mL/min

Injection volume: 20 μL

Run time: NLT 6 times the retention time of fluoride

3.3 System suitability

Samples: System suitability solution and Standard solution

[Note—The relative retention times for the fluoride and acetate ions are 1.0 and 1.1, respectively.]

3.4 Suitability requirements

Resolution: NLT 1.5 between the fluoride and acetate ions, System suitability solution

Tailing factor: NMT 2.0 for the fluoride ion, Standard solution

Relative standard deviation: NMT 0.73% for the fluoride ion, Standard solution

3.5 Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of sodium

fluoride (NaF) in the portion of Sodium Flfluoride taken:

Result = (r_U/r_S ) × (C_S /C_U ) × 100

r_U = peak response of the

fluoride ion from the Sample solution

r_S = peak response of the

fluoride ion from the Standard solution

C_S = concentration of USP Sodium Flfluoride RS in the Standard solution (μg/mL)

C_U = concentration of Sodium Flfluoride in the Sample solution (μg/mL) (USP 1-Aug-2021)

Acceptance criteria: 98.0%–102.0% on the dried basis

4 IMPURITIES

Change to read:

Chloride

[Note—Store all solutions in plastic containers. It is recommended to use plastic HPLC vials. Use water with a resistivity of NLT 18 megohm- cm to prepare the solutions.]

Mobile phase and Chromatographic system: Proceed as directed in the Assay.

System suitability solution: 1.0 mg/mL of USP Sodium Flfluoride RS and 1.0 μg/mL of USP Sodium Chloride RS in water

Standard solution: 0.2 μg/mL of USP Sodium Chloride RS in water

Sample solution: 1.0 mg/mL of Sodium Flfluoride in water

System suitability

Samples: System suitability solution and Standard solution

[Note—The relative retention times for the fluoride and chloride ions are 1.0 and 1.6, respectively.]

Suitability requirements

Resolution: NLT 4 between the

fluoride and chloride ions, System suitability solution

Relative standard deviation: NMT 5.0% for the chloride ion, Standard solution

Signal-to-noise ratio: NLT 20, Standard solution

Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of chloride ion in the portion of Sodium Flfluoride taken:

Result = (r_U/r_S ) × (C_S /C_U) × (A_r /M_r ) × 100

r_U = peak response of the chloride ion from the Sample solution

r_S = peak response of the chloride ion from the Standard solution

C_S = concentration of USP Sodium Chloride RS in the Standard solution (μg/mL)

C_U = concentration of Sodium Flfluoride in the Sample solution (μg/mL)

A_r = atomic weight of chloride, 35.453

M_r = molecular weight of sodium chloride, 58.44

Acceptance criteria: NMT 0.012% (USP 1-Aug-2021)

5 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〉

Analysis: Dry at 150° for 4 h.

Acceptance criteria: NMT 1.0%

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.

6 ADDITIONAL REQUIREMENTS

Packaging and Storage: Preserve in well-closed containers.

Add the following:

USP Reference Standards 〈11〉

USP Sodium Acetate RS

USP Sodium Chloride RS

USP Sodium Flfluoride RS (USP 1-Aug-2021)