Menthol 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

Menthol Lozenges contain NLT 90.0% and NMT 125.0% of the labeled amount of menthol (C₁₀H₂₀O), in a suitable molded base.

2 IDENTIFICATION

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

3 ASSAY

Procedure

Solution A: 250 mg/mL of sodium chloride in water

Internal standard solution: 2 mg/mL of Anethole in hexanes

Standard solution: 0.20L mg/mL of USP Menthol RS in Internal standard solution, where L is the labeled quantity, in mg, of menthol in each Lozenge

Sample solution: Transfer 20 Lozenges to a 1-L screw-capped conical flask. [Note—Use caps with inert white rubber liners.] Add 200 mL of water, 260 mL of Solution A, and 100.0 mL of the Internal standard solution, and shake by mechanical means for 30 min. Allow the phases to separate, and transfer a portion of the hexanes phase to a suitable container.

Chromatographic system

(See Chromatography 〈621〉, System Suitability.)

Mode: GC

Detector: Flame ionization

Column: 0.53-mm × 30-m fused silica; coated with a 1-μm layer of G16 stationary phase

Temperatures

Column: 125° (isothermally)

Injection port: 250°

Detector: 250°

Carrier gas: Helium

Flow rate: 10 mL/min

Injection volume: 1 μL

Injection type: Split ratio of 10:1

System suitability

Sample: Standard solution

[Note—The relative retention times for menthol and anethole are about 0.5 and 1.0, respectively.]

Suitability requirements

Resolution: NLT 15 between menthol and anethole

Tailing factor: NMT 2.0 for menthol and anethole

Relative standard deviation: NMT 2.0% for replicate injections

Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of the labeled amount of menthol (₁₀H₂₀O) in the portion of Lozenges taken:

Result = (R_U/R_S) × (C_S/C_U) × 100

R_U = peak response ratio of the menthol to the anethole from the Sample solution

R_S = peak response ratio of the menthol to the anethole from the Standard solution

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

C_U = nominal concentration of menthol in the hexanes phase of the Sample solution (mg/mL)

Acceptance criteria: 90.0%–125.0%

4 ADDITIONAL REQUIREMENTS

Packaging and Storage: Preserve in well-closed containers.

USP Reference Standards 〈11〉

USP Menthol RS