Sodium Fluoride Oral Solution

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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1 DEFINITION

Sodium Fluoride Oral Solution contains NLT 90.0% and NMT 110.0% of the labeled amount of sodium fluoride (NaF).

2 IDENTIFICATION

A. The retention time of the fluoride peak of the Sample solution corresponds to that of the Standard solution, as obtained in the Assay.

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

Sample solution: 10 mg/mL of sodium in Oral Solution. If necessary, reduce the volume of a portion of Oral Solution by heating on a steam bath.

Acceptance criteria: Meets the requirements

3 ASSAY

Procedure

[Note—Use water with a resistivity of NLT 18 megohm-cm to prepare the solutions.]

Mobile phase: 150 mg/L of anhydrous sodium carbonate and 1.0 mL/L of 1 N sodium hydroxide in water. Pass through a suitable filter of 0.45-μm pore size.

System suitability solution: 1.0 μg/mL of USP Sodium Fluoride RS and 0.5 μg/mL of USP Sodium Chloride RS in water

Standard solution: 1.1 μg/mL of USP Sodium Fluoride RS in water

Sample solution: Nominally 1.1 μg/mL of sodium fluoride from a portion of Oral Solution in water

Chromatographic system

(See Chromatography 〈621〉, System Suitability.)

Mode: LC

Detector: Conductivity with suppression

Columns

Guard: 4.0-mm × 5-cm; 10-μm packing L46

Analytical: 4.0-mm × 25-cm; 10-μm packing L46

Flow rate: 1.0 mL/min

Injection volume: 20 μL

[Note—It is recommended to use polymethylpentene HPLC vials.]

Run time: NLT 2 times the retention time of the fluoride peak

System suitability

Sample: System suitability solution

[Note—The relative retention times for fluoride and chloride ions are 1.0 and 1.2, respectively.]

Suitability requirements

Resolution: NLT 1.5 between fluoride and chloride ions

Tailing factor: NMT 2.0 for fluoride ion

Relative standard deviation: NMT 2.0% for fluoride ion

Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of the labeled amount of sodium fluoride (NaF) in the portion of Oral Solution taken:

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

r_U = peak response of fluoride from the Sample solution

r_S = peak response of fluoride from the Standard solution

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

C_U = nominal concentration of sodium fluoride in the Sample solution (μg/mL)

Acceptance criteria: 90.0%–110.0%

4 ADDITIONAL REQUIREMENTS

Packaging and Storage: Preserve in tight containers; use plastic containers for Oral Solution having a pH below 7.5.

Labeling: Label the Oral Solution in terms of the content of sodium fluoride (NaF) and in terms of the content of fluoride ion.

USP Reference Standards 〈11〉

USP Sodium Chloride RS

USP Sodium Fluoride RS