Benzocaine

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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Benzocaine

C₉H₁₁NO₂ 165.19

Benzoic acid, 4-amino-, ethyl ester;

Ethyl p-aminobenzoate

CAS RN®: 94-09-7; UNII: U3RSY48JW5.

1 DEFINITION

Benzocaine, dried over phosphorus pentoxide for 3 h, contains NLT 98.0% and NMT 102.0% of benzocaine (C₉H₁₁NO₂).

2 IDENTIFICATION

A. Spectroscopic Identification Tests 〈197〉, Infrared Spectroscopy: 197K

Sample: Previously dried over phosphorus pentoxide for 3 h

Acceptance criteria: Meets the requirements

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: Acetic acid, triethylamine, and water (20:1:980). The pH should be between 2.95 and 3.0 (adjust as needed).

Mobile phase: Methanol and Solution A (40:60)

Standard solution: 0.024 mg/mL of USP Benzocaine RS in Mobile phase

Sample solution: 0.024 mg/mL of Benzocaine in Mobile phase

Chromatographic system

(See Chromatography 〈621〉, System Suitability.)

Mode: LC

Detector: UV 285 nm

Column: 2.0-mm × 15-cm; 5-µm packing L11

Flow rate: 0.2 mL/min

Injection volume: 10 µL

System suitability

Sample: Standard solution

Suitability requirements

Tailing factor: NMT 2.0

Relative standard deviation: NMT 2.0%

Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of benzocaine (C₉H₁₁NO₂) in the portion of Benzocaine taken:

Result = (rᵤ/rₛ) × (Cₛ/Cᵤ) × 100

rᵤ = peak response from the Sample solution

rₛ = peak response from the Standard solution

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

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

Acceptance criteria: 98.0%–102.0% on the previously dried basis

4 IMPURITIES

Residue on Ignition 〈281〉: NMT 0.1%

Chloride

Analysis: To a solution of 200 mg in 5 mL of alcohol, previously acidified with a few drops of diluted nitric acid, add a few drops of silver nitrate TS.

Acceptance criteria: No turbidity is produced immediately.

Organic Impurities

Solution A: Add 1.0 mL of trifluoroacetic acid in 1 L of water.

Solution B: Acetonitrile

Mobile phase: See Table 1.

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

Standard stock solution: 0.1 mg/mL each of USP Benzocaine RS, USP Aminobenzoic Acid RS, and USP Ethyl 4-nitrobenzoate RS in Diluent. Sonicate for 2–5 min to dissolve before diluting to final volume.

Standard solution: 1 µg/mL each of USP Benzocaine RS, USP Aminobenzoic Acid RS, and USP Ethyl 4-nitrobenzoate RS in Diluent from the Standard stock solution

Sample solution: 1 mg/mL of Benzocaine in Diluent. Sonicate for 2–5 min to assist in dissolution as needed before diluting to final volume.

Chromatographic system

(See Chromatography 〈621〉, System Suitability.)

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

Suitability requirements

Resolution: NLT 10 from any two peaks

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 Benzocaine 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 corresponding reference standard from the Standard solution

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

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

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

Result = (rᵤ/rₛ) × (Cₛ/Cᵤ) × 100

rᵤ = peak response of any other individual 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 = concentration of Benzocaine in the Sample solution (mg/mL)

Acceptance criteria: See Table 2. Disregard peaks less than 0.05%.

5 SPECIFIC TESTS

Loss on Drying 〈731〉

Analysis: Dry over phosphorus pentoxide for 3 h.

Acceptance criteria: NMT 1.0%

6 ADDITIONAL REQUIREMENTS

Packaging and Storage: Preserve in well-closed containers.

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