Benzethonium Chloride Topical 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

Benzethonium Chloride Topical Solution contains NLT 95.0% and NMT 105.0% of the labeled amount of benzethonium chloride (C₂₇H₄₂ClNO₂).

2 IDENTIFICATION

Change to read:

A. The UV absorption spectra of the major peak of the Sample solution corresponds to that of the Standard solution, as obtained in the Assay (USP 1-May-2022)

Change to read:

B. The retention time of the major peak of the Sample solution corresponds to that of the Standard solution, as obtained in the Assay. (USP 1-May-2022)

3 ASSAY

Change to read:

3.1 PROCEDURE

Buffer: 20 mL/L of triethylamine in water. Adjust with phosphoric acid to a pH of 3.0.

Mobile phase: Acetonitrile and Buffer (42:58)

Diluent: Acetonitrile and water (40:60)

Standard solution: 0.2 mg/mL of USP Benzethonium Chloride RS in Diluent. Sonication may be necessary for complete dissolution.

Sample solution: Nominally equivalent to 0.2 mg/mL of benzethonium chloride in Diluent prepared as follows. Weigh an amount of Topical Solution equivalent to 2 mg of benzethonium chloride into a 50-mL round-bottom flask. Evaporate on a rotavap under vacuum and heat at 35° to dryness. Pipette 10 mL of Diluent and sonicate for about 10 min and mix. Pass the solution through a suitable filter of 0.2-um pore size discarding the first 1-2 mL.

Chromatographic system

(See Chromatography (621), System Suitability.)

Mode: LC

Detector: UV 225 nm. For Identification A, use a diode array detector in the range of 200-400 nm.

Column: 4.6-mm x 15 cm; 5-µm packing L7

Column temperature: 40°

Flow rate: 1 mL/min

Injection volume: 10 µL

System suitability

Sample: Standard solution

Suitability requirements

Tailing factor: NMT 2.0

Relative standard deviation: NMT 1.0%

Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of the labeled amount of benzethonium chloride (C₂₇H₄₂ClNO₂) in the portion of Topical Solution taken:

Result = (r_U/r_S) × (C_S/C_U) × 100

r_U = peak response of benzethonium from the Sample solution

r_S = peak response of benzethonium from the Standard solution 

C_S = concentration of USP Benzethonium Chloride RS in the Standard solution (mg/mL)

C_U = nominal concentration of benzethonium chloride in the Sample solution (mg/mL) (USP 1-May-2022)

Acceptance criteria: 95.0%-105.0%

4 IMPURITIES

Add the following:

4.1 ORGANIC IMPURITIES

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

System suitability solution: 0.15 mg/mL each of USP Benzethonium Chloride RS and USP Methylbenzethonium Chloride RS in Diluent.

Sonication may be necessary for complete dissolution.

Standard solution: 0.002 mg/mL of USP Benzethonium Chloride RS in Diluent. Sonication may be necessary for complete dissolution.

Sensitivity solution: 0.001 mg/mL of USP Benzethonium Chloride RS in Diluent from Standard solution

Sample solution: Nominally equivalent to 1 mg/mL of benzethonium chloride in Diluent prepared as follows. Weigh an amount of Topical Solution equivalent to 10 mg of benzethonium chloride into a 10-mL volumetric flask. Evaporate on rotavap under vacuum and heat at 35° to dryness. Add about 8 mL of Diluent, sonicate for about 10 min, and dilute with Diluent to volume. Pass the solution through a suitable filter of 0.2-µm pore size discarding the first 1-2 mL.

System suitability

Samples: System suitability solution, Standard solution, and Sensitivity solution

[NOTE-The relative retention times for benzethonium and methylbenzethonium are 1.0 and 1.47, respectively.]

Suitability requirements

Resolution: NLT 7.0 between benzethonium and methylbenzethonium peaks, System suitability solution

Relative standard deviation: NMT 5.0%, Standard solution

Signal-to-noise ratio: NLT 10.0%, Sensitivity solution

Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of each impurity in the portion of the sample taken:

Result = (r_U/r_S) × (C_S/C_U) × 100

r_U = peak response of each impurity from the Sample solution

r_S = peak response of benzethonium from the Standard solution

C_S = concentration of USP Benzethonium Chloride RS in the Standard solution (mg/mL)

C_U = nominal concentration of benzethonium chloride in the Sample solution (mg/mL)

Acceptance criteria

Total impurities: NMT 1.0% (USP 1-May-2022)

Change to read:

4.2 (USP 1-MAY-2022) LIMIT OF NITRITES

Naphthylamine solution: Boil 30 mg of 1-naphthylamine in 70 mL of water. Decant the colorless solution from the blue-violet residue, and mix with 30 mL of glacial acetic acid. (USP 1-May-2022)

Sample: One drop of Topical Solution on a spot plate

Analysis: To the Sample add one drop each of glacial acetic acid, sulfanilic acid in acetic acid (1 in 100), and Naphthylamine solution.▲ (USP 1-May-2022)

Acceptance criteria: No red color develops in the resulting solution within 10 min.

5 SPECIFIC TESTS

Delete the following:

5.1 OXIDIZING SUBSTANCES

Sample: 5 mL

Analysis: To the Sample add 0.5 mL of potassium iodide TS and a few drops of 3 N hydrochloric acid.

Acceptance criteria: The solution does not acquire a yellow color. (USP 1-May-2022)

6 ADDITIONAL REQUIREMENTS

PACKAGING AND STORAGE: Preserve in tight, light-resistant containers.

Add the following:

USP REFERENCE STANDARDS (11)

USP Benzethonium Chloride RS

USP Methylbenzethonium Chloride RSA (USP 1-May-2022)