Sodium Mono Fluorophosphate

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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Na₂PFO₃ 143.95

Phosphoro fluoridic acid, disodium salt;

Disodium phosphoro fluoridate CAS RN®: 10163-15-2; UNII: C810JCZ56Q.

1 DEFINITION

Sodium Mono Fluorophosphate contains NLT 91.7% and NMT 100.5% of sodium mono

Fluorophosphate (Na₂PFO₃ ), calculated on the dried basis.

2 IDENTIFICATION

A. The retention time of the mono Fluorophosphate 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: Meets the requirements

3 ASSAY

3.1 Procedure

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

Solution A: 100 mM potassium hydroxide in water

Solution B: Water

Mobile phase: See Table 1.

Table 1

Alternatively, Mobile phase can be generated electrolytically using an automatic eluent generator.

System suitability solution: 4.0 μg/mL of USP Sodium Fluoride RS, 1.4 μg/mL of USP Sodium Acetate RS, 150 μg/mL of USP Sodium

MonoFluorophosphate RS, and 150 μg/mL of USP Sodium Sulfate Anhydrous RS in water

Standard solution: 150 μg/mL of USP Sodium Monofluorophosphate RS in water

Sample solution: 150 μg/mL of Sodium Mono Fluorophosphate 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

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

Column temperature: 40°

Flow rate: 1.0 mL/min

Injection volume: 10 μL

3.3 System suitability

Samples: System suitability solution and Standard solution

[Note—The relative retention times for fluoride, acetate, mono Fluorophosphate, and sulfate ions are 0.16, 0.18, 1.0, and 1.1, respectively.]

3.4 Suitability requirements

Resolution: NLT 1.5 between the mono

Fluorophosphate and sulfate ions, System suitability solution

Tailing factor: NMT 2.5 for the mono

Fluorophosphate ion, Standard solution

Relative standard deviation: NMT 2.0% for the mono

Fluorophosphate ion, Standard solution

3.5 Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of sodium mono

Fluorophosphate (Na₂PFO₃) in the portion of Sodium Mono

Fluorophosphate taken:

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

r_U = peak response of mono Fluorophosphate from the Sample solution

r_S = peak response of mono Fluorophosphate from the Standard solution

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

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

Acceptance criteria: 91.7%–100.5% on the dried basis

4 IMPURITIES

Change to read:

Arsenic 〈211〉, Procedures, Procedure 1 (CN 1-Jun-2023) : NMT 3 ppm

Limit of Fluoride Ion

[Note—Use plasticware throughout this test.]

Solution A, Solution B, Mobile phase, System suitability solution, Sample solution, and Chromatographic system: Proceed as directed in the Assay.

Standard solution: 4.0 μg/mL of USP Sodium Fluoride RS in water

4.1 System suitability

Samples: System suitability solution and Standard solution

[Note—The relative retention times for

uoride, acetate, mono

Fluorophosphate, and sulfate ions are 0.16, 0.18, 1.0, and 1.1, respectively.]

4.2 Suitability requirements

Resolution: NLT 1.5 between the

uoride and acetate ions, System suitability solution

Relative standard deviation: NMT 5.0% for the

uoride ion, Standard solution

4.3 Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of

uoride ion in the portion of Sodium Mono

Fluorophosphate taken:

Result = (r_U/r_S ) × (C_S /C_U) × (A /M ) × 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 = concentration of Sodium Mono

Fluorophosphate in the Sample solution (μg/mL)

A_r = atomic weight of fluoride, 19.00

M_r = molecular weight of sodium fluoride, 41.99

Acceptance criteria: NMT 1.2%

5 SPECIFIC TESTS

pH 〈791〉

Sample solution: 20 mg/mL of Sodium Mono

Fluorophosphate in water

Acceptance criteria: 6.5–8.0

Loss on Drying 〈731〉

Analysis: Dry at 105° to constant weight.

Acceptance criteria: NMT 0.2%

6 ADDITIONAL REQUIREMENTS

Packaging and Storage: Preserve in tight containers.

USP Reference Standards 〈11〉

USP Sodium Acetate RS

USP Sodium Fluoride RS

USP Sodium MonoFluorophosphate RS

USP Sodium Sulfate Anhydrous RS