Benzoyl Peroxide Lotion

This article is compiled based on the United States Pharmacopeia (USP) – 2025 Edition

Issued and maintained by the United States Pharmacopeial Convention (USP)

DOWNLOAD PDF HERE

1 DEFINITION

Benzoyl peroxide Lotion is benzoyl peroxide in a suitable lotion base. It contains NLT 90.0% and NMT 110.0% of the labeled amount of benzoyl peroxide (C₁₄H₁₀O₄).

2 IDENTIFICATION

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

3 ASSAY

Procedure

Mobile phase: Acetonitrile in water (5 in 10)

Internal standard solution: 3.6 mg/mL of ethyl benzoate in acetonitrile

Standard stock solution: Transfer a suitable quantity of benzoyl peroxide, recently subjected to the Assay under Hydrous Benzoyl Peroxide, in a weighed conical flask fitted with a glass stopper. Weigh again to obtain the weight of the specimen, and quantitatively dissolve in acetonitrile to obtain a solution containing 0.8 mg/mL.

Standard solution: 10 mL of Standard stock solution and 5 mL of Internal standard solution. Dilute with acetonitrile to 25 mL. This Standard solution contains 0.32 mg/mL of benzoyl peroxide.

Sample stock solution: Transfer the equivalent to 40 mg of benzoyl peroxide from Lotion in a 50-mL volumetric flask, and add 40 mL of acetonitrile. Shake vigorously until the material is thoroughly dispersed. Sonicate the mixture for 5 min, dilute with acetonitrile to volume, mix, and filter.

Sample solution: 10 mL of Sample stock solution and 5 mL of Internal standard solution. Dilute with acetonitrile to 25 mL.

Chromatographic system

(See Chromatography 〈621〉, System Suitability.)

Mode: LC

Detector: UV 254 nm

Column: 3.9-mm × 30-cm; packing L1

Flow rate: 1 mL/min

Injection volume: 10 µL

System suitability

Sample: Standard solution (three replicate injections)

[Note—The retention times for ethyl benzoate and benzoyl peroxide are 7 and 14 min, respectively.]

Suitability requirements

Resolution: NLT 2.0 between ethyl benzoate and benzoyl peroxide

Tailing factor: NMT 2.0 for the ethyl benzoate and benzoyl peroxide peaks

Peak response ratios: The lowest and highest peak response ratios (R) agree within 2.0%.

Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of the labeled amount of benzoyl peroxide (C₁₄H₁₀O₄) in the portion of Lotion taken:

Result = (Rᵤ/Rₛ) × (Cₛ/Cᵤ) × 100

Rᵤ = peak response ratio of benzoyl peroxide to ethyl benzoate from the Sample solution

Rₛ = peak response ratio of benzoyl peroxide to ethyl benzoate from the Standard solution

Cₛ = concentration of benzoyl peroxide in the Standard solution (mg/mL)

Cᵤ = nominal concentration of benzoyl peroxide in the Sample solution (mg/mL)

Acceptance criteria: 90.0%–110.0%.

4 IMPURITIES

Organic Impurities

Solution A: Acetonitrile and glacial acetic acid (1000:1)

Solution B: Glacial acetic acid and water (1:1000)

Mobile phase: See Table 1.

System suitability solution: 100 µg/mL of benzoic acid and 60 µg/mL of methylparaben in acetonitrile

Standard solution A: 500 µg/mL of benzoic acid in acetonitrile

Standard solution B: 20 µg/mL of ethyl benzoate in acetonitrile

Standard solution C: 20 µg/mL of benzaldehyde in acetonitrile

Standard solution D: Prepare a solution of hydrous benzoyl peroxide, previously subjected to the Assay under Hydrous Benzoyl Peroxide, in acetonitrile containing the equivalent of 40 µg/mL of anhydrous benzoyl peroxide.

Sample solution: Equivalent to 100 mg of benzoyl peroxide from Lotion. In a 50-mL volumetric flask add 25 mL of acetonitrile, and shake vigorously to disperse the specimen. Sonicate for 5 min, dilute with acetonitrile to volume, mix, and filter.

Chromatographic system

(See Chromatography 〈621〉, System Suitability.)

Mode: LC

Detector: UV 235 nm

Column: 4.6-mm × 25-cm; packing L1

Flow rate: 1.2 mL/min

Injection volume: 10 µL

System suitability

Sample: System suitability solution

Suitability requirements

Resolution: NLT 2.0 between benzoic acid and methylparaben

Tailing factor: NMT 2.0 for the benzoic acid and methylparaben peaks

Analysis

Samples: Standard solution and Sample solution

Acceptance criteria: The responses of any peaks from the Sample solution corresponding to benzoic acid, ethyl benzoate, and benzaldehyde are NMT those of the main peaks from Standard solution A (25%), Standard solution B (1%), and Standard solution C (1%), respectively. The response of any other impurity peak from the Sample solution, other than the main benzoyl peroxide peak, any benzoic acid, ethyl benzoate, benzaldehyde, methylparaben, or Propylparaben peak, and any solvent peak, is NMT that from Standard solution D (2%); and the sum of the responses of all the impurity peaks, other than those of benzoic acid, ethyl benzoate, and benzaldehyde, is NMT that from Standard solution D (2%).

5 SPECIFIC TESTS

pH 〈791〉: 2.8–6.6

6 ADDITIONAL REQUIREMENTS

Packaging and Storage: Preserve in tight containers.