Benzocaine Lozenges

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 Lozenges contain NLT 85.0% and NMT 120.0% of the labeled amount of benzocaine (C₉H₁₁NO₂).

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

3.1 PROCEDURE

Buffer: 1.0 M monobasic potassium phosphate, adjusted with phosphoric acid to a pH of 3.0

Mobile phase: Acetonitrile, water, and Buffer (250:700:50)

Diluent A: 0.1 N hydrochloric acid

Diluent B: Acetonitrile and water (1:1)

Standard solution A: 0.01 mg/mL of USP Benzocaine RS in Diluent A

Standard solution B: 0.01 mg/mL of USP Benzocaine RS in Diluent B

Sample stock solution A: Transfer the equivalent of 40 mg of benzocaine from powdered Lozenges (NLT 20) to a 200-mL volumetric flask.

Add 150 mL of Diluent A, and stir for NLT 2 h. Dilute with Diluent A to volume.

Sample stock solution B: Transfer the equivalent of 40 mg of benzocaine from powdered Lozenges (NLT 20) to a 200-mL volumetric flask.

Add 150 mL of Diluent B, and stir for NLT 30 min. Dilute with Diluent B to volume.

Sample solution A: Nominally 0.01 mg/mL of benzocaine in Diluent A from Sample stock solution A

Sample solution B: Nominally 0.01 mg/mL of benzocaine in Diluent B from Sample stock solution B

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 x 25-cm; packing L7

Flow rate: 1.5 mL/min

Injection volume: 20 µL

System suitability

Samples: Standard solution A and Standard solution B

Suitability requirements

Tailing factor: NMT 1.5

Relative standard deviation: NMT 2.0%

Analysis

Samples: Standard solution A, Standard solution B, Sample solution A, and Sample solution B

Calculate the percentage of the total labeled amount of benzocaine (C₉H₁₁NO₂) in the portion of Lozenges taken:

Result = (r_U/r_S) × (C_S/C_U) × 100

r_U = peak response from Sample solution A

r_S = peak response from Standard solution A 

C_S = concentration of USP Benzocaine RS in Standard solution A (mg/mL)

C_U = nominal concentration of benzocaine in Sample solution A (mg/mL)

Calculate the percentage of free benzocaine (CH, NO) in the portion of Lozenges taken:

Result = (r_U/r_S) × (C_S/C_U) × 100

r_U = peak response from Sample solution B

r_S = peak response from Standard solution B

C_S = concentration of USP Benzocaine RS in Standard solution B (mg/mL)

C_U = nominal concentration of benzocaine in Sample solution B (mg/mL)

Acceptance criteria

Total labeled amount of benzocaine: 85.0%-120.0%

Free benzocaine: 85.0%-120.0%

4 IMPURITIES

4.1 ORGANIC IMPURITIES

Solution A: Dissolve 9.1 g of monobasic potassium phosphate in 1000 mL of water. Adjust with phosphoric acid to a pH of 3.0.

Solution B: Acetonitrile

Mobile phase: See Table 1.

Table 1

Diluent: Acetonitrile and water (10:90)

Standard stock solution: 0.03 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: 0.3 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: Nominally 150 µg/mL of benzocaine in Diluent prepared as follows. Transfer 10 Lozenges to an appropriate volumetric flask to obtain a nominal benzocaine concentration of 0.15 mg/mL. Dissolve Lozenges in Diluent and dilute with Diluent to volume.

Chromatographic system

(See Chromatography (621), System Suitability.)

Mode: LC

Detector: UV 280 nm

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

Flow rate: 1.5 mL/min

Injection volume: 100 µL

System suitability

Sample: Standard solution

Suitability requirements

Resolution: NLT 10 between benzocaine and aminobenzoic acid; NLT 10 between ethyl 4-nitrobenzoate and benzocaine

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 Lozenges taken:

Result = (r_U/r_S) × (C_S/C_U) × 100

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

r_S = peak response of the corresponding Reference Standard from the Standard solution

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

C_U = nominal concentration of benzocaine in the Sample solution (µg/mL)

Calculate the percentage of each unspecified degradation product in the portion of Lozenges taken:

Result = (r_U/r_S) × (C_S/C_U) × 100

r_U = peak response of each unspecified degradation product from the Sample solution

r_S = peak response of benzocaine from the Standard solution

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

C_U = nominal concentration of benzocaine in the Sample solution (µg/mL)

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

Table 2

5 ADDITIONAL REQUIREMENTS

PACKAGING AND STORAGE: Preserve in well-closed containers, and store at controlled room temperature.

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