Sodium Fluoride Gel

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 Gel contains NLT 90.0% and NMT 110.0% of the labeled amount of sodium fluoride (NaF), in an aqueous medium containing a suitable viscosity-inducing agent. It may contain a suitable buffering agent.

[Note—This monograph is only applicable to Preventive treatment gels and is not applicable to Dentifrices as defined under 21 CFR §355.3.]

1.1 IDENTIFICATION

Change to read:

A. (USP 1-May-2020)

Sample: A suitable quantity of Gel, equivalent to 500 mg of fluoride ion

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 dry.

Acceptance criteria: The surface of the glass is etched.

Add the following:

B. 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-May-2020)

2 ASSAY

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2.1 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 Fluoride RS and 1.0 μg/mL of USP Sodium Acetate RS in water

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

Sample solution: Nominally 2.0 μg/mL of sodium fluoride from a portion of Gel in water

2.2 Chromatographic system

(See Chromatography 〈621〉, System Suitability.)

Mode: LC

Detector: Conductivity with suppression

Columns

Guard: 4.0-mm × 0.5-cm; 4.6-μm packing L91

Analytical: 4.0-mm × 25-cm; 4.6-μm packing L91

Column temperature: 40°

Flow rate: 1.0 mL/min

Injection volume: 20 μL

Run time: NLT 3 times the retention time of fluoride

2.3 System suitability

Samples: System suitability solution and Standard solution

[Note—The relative retention times for the fluoride and acetate ions are 1.0 and 1.3, respectively.]

2.4 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 2.0% for the fluoride ion, Standard solution

2.5 Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of the labeled amount of sodium fluoride (NaF) in the portion of Gel 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 Fluoride RS in the Standard solution (μg/mL)

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

(USP 1-May-2020)

Acceptance criteria: 90.0%–110.0%

3 SPECIFIC TESTS

pH 〈791〉

Sample: About 40 mL

Analysis: Place the Sample in a plastic beaker, and determine the pH using a suitable electrode system.

Acceptance criteria: 6.0–8.0

4 ADDITIONAL REQUIREMENTS

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Packaging and Storage: Preserve in tight, plastic containers. Store at controlled room temperature. (USP 1-May-2020)

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

Change to read:

USP Reference Standards 〈11〉

USP Sodium Acetate RS (USP 1-May-2020)

USP Sodium Fluoride RS