Benzocaine 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

Benzocaine Topical Solution is a solution of Benzocaine in a suitable solvent. It contains NLT 90.0% and NMT 110.0% of the labeled amount of benzocaine (C₉H₁₁NO₂). It contains a suitable antimicrobial agent.

2 IDENTIFICATION

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

B. 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

Solution A: 0.1% Trifluoroacetic acid, prepared by diluting 1.0 mL of trifluoroacetic acid with water to 1 L

Solution B: Acetonitrile

Mobile phase: See Table 1.

Diluent: Solution A and Solution B (1:1)

System suitability solution: 1 µg/mL of USP Benzocaine RS and 2 µg/mL each of USP Aminobenzoic Acid RS and USP Ethyl 4-Nitrobenzoate RS in Diluent

Standard solution: 0.1 mg/mL of USP Benzocaine RS in Diluent

Sample solution: Nominally 0.1 mg/mL of benzocaine in Diluent prepared as follows. Transfer 10 mg of benzocaine from a portion of Topical Solution to a 100-mL volumetric flask, and dilute with Diluent to volume. Pass through a suitable filter of 0.45-µm pore size as needed, discarding the first 2–3 mL of filtrate.

Chromatographic system

(See Chromatography 〈621〉, System Suitability.)

Mode: LC

Detector: UV 280 nm. For Identification test A, use a diode array detector in the range of 200–400 nm.

Column: 4.6-mm × 25-cm; 5-µm packing L7

Flow rate: 1.5 mL/min

Injection volume: 20 µL

System suitability

Samples: System suitability solution and Standard solution

[Note—The relative retention times for aminobenzoic acid, benzocaine, and ethyl 4-nitrobenzoate are 0.3, 1.0, and 2.1, respectively.]

Suitability requirements

Resolution: NLT 6 between aminobenzoic acid and benzocaine; and between benzocaine and ethyl 4-nitrobenzoate, System suitability solution

Tailing factor: NMT 1.5, Standard solution

Relative standard deviation: NMT 1.0%, Standard solution

Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of the labeled amount of benzocaine (C₉H₁₁NO₂) in the portion of Topical Solution taken:

Result = (rᵤ/rₛ) × (Cₛ/Cᵤ) × 100

rᵤ = peak response of benzocaine from the Sample solution

rₛ = peak response of benzocaine from the Standard solution

Cₛ = concentration of USP Benzocaine RS in the Standard solution (mg/mL)

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

Acceptance criteria: 90.0%–110.0%

4 IMPURITIES

Organic Impurities

Solution A: 0.1% Trifluoroacetic acid, prepared by diluting 1.0 mL of trifluoroacetic acid with water to 1 L

Solution B: Acetonitrile

Mobile phase: See Table 2.

Diluent: Solution A and Solution B (1:1)

Standard solution: 1 µg/mL of USP Benzocaine RS and 2 µg/mL each USP Aminobenzoic Acid RS and USP Ethyl 4-Nitrobenzoate RS in Diluent

Sample solution: Nominally 1 mg/mL of benzocaine in Diluent prepared as follows. Transfer 50 mg of benzocaine from a portion of Topical Solution to a volumetric flask and dissolve with aid of sonication as needed, then dilute with Diluent to volume. Pass through a suitable filter of 0.45-µm pore size as needed, discarding the first 2–3 mL of filtrate.

Chromatographic system

Mode: LC

Detector: UV 280 nm

Column: 4.6-mm × 25-cm; 5-µm packing L7

Flow rate: 1.5 mL/min

Injection volume: 20 µL

System suitability

Sample: Standard solution

[Note—See Table 3 for relative retention times.]

Suitability requirements

Resolution: NLT 6 between aminobenzoic acid and benzocaine; and between benzocaine and ethyl 4-nitrobenzoate

Relative standard deviation: NMT 2.0% for each peak corresponding to benzocaine, aminobenzoic acid, and ethyl 4-nitrobenzoate

Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of aminobenzoic acid and ethyl 4-nitrobenzoate in the portion of Topical Solution taken:

Result = (rᵤ/rₛ) × (Cₛ/Cᵤ) × 100

rᵤ = peak response of aminobenzoic acid or ethyl 4-nitrobenzoate from the Sample solution

rₛ = peak response of aminobenzoic acid or ethyl 4-nitrobenzoate from the Standard solution

Cₛ = concentration of USP Aminobenzoic Acid RS or USP Ethyl 4-Nitrobenzoate RS in the Standard solution (mg/mL)

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

Calculate the percentage of any other individual unspecified impurity in the portion of Topical Solution taken:

Result = (rᵤ/rₛ) × (Cₛ/Cᵤ) × 100

rᵤ = peak response of any other individual unspecified impurity from the Sample solution

rₛ = peak response of benzocaine from the Standard solution

Cₛ = concentration of USP Benzocaine RS in the Standard solution (mg/mL)

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

Acceptance criteria: See Table 3. Disregard peaks less than 0.05%.

5 SPECIFIC TESTS

Microbial Enumeration Tests 〈61〉 and Tests for Specified Microorganisms 〈62〉: It meets the requirements of the tests for absence of Staphylococcus aureus and Pseudomonas aeruginosa.

6 ADDITIONAL REQUIREMENTS

Packaging and Storage: Preserve in tight containers, protected from light, and avoid prolonged exposure to temperatures exceeding 30°.

USP Reference Standards 〈11〉

USP Aminobenzoic Acid RS

Benzoic acid, 4-amino. C₇H₇NO₂ 137.14

USP Benzocaine RS

USP Ethyl 4-Nitrobenzoate RS

Benzoic acid, 4-nitro-, ethyl ester. C₉H₉NO₄ 195.17