Stannous 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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1 DEFINITION

Stannous Fluoride contains NLT 71.2% of stannous tin (Sn²⁺ (USP 1-Aug-2022) ), and NLT 22.3% and NMT 25.5% of fluoride (F− (USP 1-Aug- 2022) ), calculated on the dried basis.

2 IDENTIFICATION

Change to read:

A. The retention time of the fluoride peak of the Sample solution corresponds to that of the Standard solution, as obtained in the Assay, Procedure 2: Fluoride. (USP 1-Aug-2022)

B.

Sample solution: 10 mg/mL of Stannous Fluoride in water

Analysis: On a spot plate, mix 2 drops of the Sample solution with 2 drops of silver nitrate TS. Acceptance criteria: A brown-black precipitate is formed.

C.

Sample solution: 10 mg/mL of Stannous Fluoride in water

Analysis: Add 1 drop of the Sample solution to 2 drops of mercuric chloride TS.

Acceptance criteria: A white, silky precipitate is formed. On further addition of the Sample solution, a brown-black precipitate is formed.

3 ASSAY

Change to read:

3.1 PROCEDURE 1: STANNOUS TIN (USP 1-A -2022)

Solution A: 5 mg/mL of sodium hy droxide and 50 mg/mL of potassium iodide in oxygen-free water

Potassium iodide–iodate solution: 0.1 N potassium iodide–iodate solution prepared as follows. In a 1000-mL volumetric flask, dissolve

3.567 g of potassium iodate, previously dried at 110° to constant weight, in 200 mL of Solution A, and dilute with oxygen-free water to volume. Standardize this solution by titrating a solution prepared from an accurately weighed quantity of tin (Sn) and hy drochloric acid. Each milliliter of 0.1 N potassium iodide–iodate solution is equivalent to 5.935 mg of tin (Sn).

Sample: 250 mg of Stannous Fluoride Titrimetric system

(See Titrimetry 〈541〉.) (USP 1-Aug-2022)

Mode: Direct titration

Titrant: Potassium iodide–iodate solution Endpoint detection: Visual

Analysis: Transfer the Sample to a 500-mL conical flask, and add 300 mL of hot, recently boiled 3 N hy drochloric acid. While passing a stream

of an oxygen-free inert gas over the surface of the liquid, swirl the flask to dissolve the Sample, and cool to room temperature. Add 5 mL of potassium iodide TS, and titrate in an inert atmosphere with Titrant, adding 3 mL of starch TS as the endpoint is approached.

Calculate the percentage of stannous tin (Sn2+) in the portion of Stannous Fluoride taken:

Result = V_S × N × F × (1/W) × 100

V_S = volume of Titrant consumed by the Sample (mL)

N = actual Titrant concentration, in normality (mEq/mL)

F = equivalency factor of stannous tin, 59.35 mg/mEq

W = weight of the Sample taken (mg) (USP 1-Aug-2022)

Acceptance criteria: NLT 71.2% on the dried basis

Change to read:

3.2 PROCEDURE 2: FLUORIDE

[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: 3.7 µg/mL of Stannous Fluoride in water

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

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.]

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 1.0% for the fluoride ion, Standard solution Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of fluoride (F−) in the portion of Stannous Fluoride taken:

Result = (r_U/r_S) × (C_S/C_U) × (A_r/M_r) × 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 = concentration of Stannous Fluoride in the Sample solution (µg/mL)

A_r = atomic weight of fluoride, 19.00

M_r = molecular weight of sodium fluoride, 41.99 (USP 1-Aug-2022)

Acceptance criteria: 22.3%–25.5% on the dried basis

4 IMPURITIES

Change to read:

4.1 ANTIMONY

Solution A: 0.1 mg/mL of rhodamine B in 0.5 N hydrochloric acid

Standard stock solution: 0.275 mg/mL of antimony potassium tartrate in water

Standard solution: 2.75 µg/mL of antimony potassium tartrate in 6 N hydrochloric acid from the Standard stock solution Sample solution: 20 mg/mL of Stannous Fluoride in 6 N hy drochloric acid

Instrumental conditions

(See Ultraviolet-Visible Spectroscopy 〈857〉.)▲ (USP 1-Aug-2022)

Mode: Vis

Analytical wavelength: 550 nm Blank: Water

Analysis

Samples: Standard solution and Sample solution

Transfer 5 mL each of the Standard solution and the Sample solution into separate 125-mL separators, add 15 mL of hydrochloric acid and 1 g of ceric sulfate, and allow to stand for 5 min, with occasional shaking. Add 500 mg of hy droxylamine hy drochloride, and shake for 1 min. Add 15 mL of isopropyl ether into the mixture, shake for 30 s, and add 7 mL of water. Cool in a water bath at room temperature for 10 min, shake for 30 s, allow the layers to separate, and discard the aqueous phase. Add 20 mL of Solution A, shake for 30 s, and discard the aqueous layer. Decant the ether layer from the top of the separator, and centrifuge, if necessary, to obtain a clear solution. Concomitantly determine the absorbances of the ether solutions from the Standard solution and the Sample solution.

Acceptance criteria: The absorbance of the Sample solution is NMT that of the Standard solution (0.005%).

4.2 WATER-INSOLUBLE SUBSTANCES

Sample: 10 g of Stannous Fluoride

Analysis: Transfer the Sample to a 400-mL plastic beaker, add 200 mL of water, and stir with a plastic rod for 3 min, or until no more solid dissolves. Filter through a tared filtering crucible, and wash thoroughly, first with 10 mg/mL of ammonium fluoride solution, then with water. [NOTE—Prepare and use the filtering crucible in a well-ventilated hood.] Dry the residue at 105° for 4 h, cool, and weigh.

Acceptance criteria: NMT 0.2%

5 SPECIFIC TESTS

PH 〈791〉

Sample solution: 4 mg/mL of Stannous Fluoride in water, freshly prepared Acceptance criteria: 2.8–3.5

LOSS ON DRYING 〈731〉

Analysis: Dry at 105° for 4 h.

Acceptance criteria: NMT 0.5%

6 ADDITIONAL REQUIREMENTS

PACKAGING AND STORAGE: Preserve in well-closed containers. Change to read:

USP REFERENCE STANDARDS 〈11〉

USP Sodium Acetate RS (USP 1-Aug-2022)

USP Sodium Fluoride RS