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C₁₀H₂₀O 156.26 1490-04-6

Cyclohexanol, 5-methyl-2-(1-methylethyl)-. 

Category Antiflatulent.

Menthol is an alcohol obtained from oils derived from a variety of mints or prepared synthetically. Menthol may be levorotatory (l-menthol) from natural or synthetic sources, or racemic (dl-menthol). Menthol contains not less than 98.0 per cent and not more than 102.0 per cent of C₁₀H₂₀O.

Description Colourless, hexagonal crystals, usually needle-like, or infused masses, or crystalline powder. Odour, pleasant, peppermint-like.

Solubility Slightly soluble in water; very soluble in ethanol, in chloroform, in ether, and in solvent hexane; freely soluble in glacial acetic acid, in fixed oils, and in volatile oils.

Packaging and storage Menthol shall be kept in tightly closed containers and stored at a temperature not exceeding 30.

Labelling The label on the container states whether it is levorotatory or racemic.

Identification The retention time of the major peak in the chromatogram of the Assay preparation corresponds to that in the chromatogram of the Standard preparation, as obtained in the Assay.

Melting range For levomenthol, 41 to 44; for racemic menthol, about 34 (Appendix 4.3).

Optical rotation For levomenthol, -45 to -51; for racemic menthol –2 to +2, when determined in a 10.0 per cent w/v solution in absolute ethanol (Appendix 4.8).

Related substances Not more than 2.0 per cent of total impurities, not more than 0.5 per cent of isomenthol (for

synthetic racemic menthol), and not more than 0.3 per cent of all other impurities from natural and synthetic menthol. Carry out the test as described in the “Gas Chromatography” (Appendix 3.4).

Chromatographic system Proceed as directed in the Assay. (Note The relative retention time of isomenthol to synthetic racemic menthol is 1.08.)

Standard solution Prepare a solution containing 5 mg per mL of Menthol RS in hexane.

Test solution Prepare a solution containing 5 mg per mL of Menthol in hexane.

System suitability

SAMPLE Standard solution

System suitability requirements

SYMMETRY FACTOR Not more than 2.0 for the menthol peak.

Procedure Inject a portion (about 2 µL) of Standard solution and Test solution into the chromatograph. Measure the areas of the principal and related peaks in each chromatogram.

Calculation Calculate the percentage of each individual impurity in the portion of Menthol taken by normalization procedure.

Limit of nonvolatile residue Not more than 0.05 per cent w/w. Evaporate 2 g, accurately weighed, in a tared open porcelain dish on a steam-bath and dry the residue at 105° for 1 hour.

Assay Carry out the determination as described in the “Gas Chromatography” (Appendix 3.4).

Internal standard preparation Dissolve an accurately weighed quantity of Anethole RS in hexane to obtain a solution having a known concentration of 10 mg per mL.

Standard preparation Transfer about 50 mg of Menthol RS, accurately weighed, and 5.0 mL of Internal standard preparation to a 100-mL volumetric flask, dissolve in and dilute with hexane to volume. Mix well to obtain a solution containing 500 µg per mL of menthol and 500 µg per mL of anethole.

Assay preparation Transfer about 50 mg of Menthol, accurately weighed, and 5.0 mL of Internal standard preparation to a 100-mL volumetric flask, dissolve in and dilute with hexane to volume. Mix well to obtain a solution containing 500 µg per mL of menthol and 500 µg per mL of anethole.

Chromatographic system

DETECTOR Flame ionization.

COLUMN A fused-silica (30 m × 0.53 mm) coated with polyethylene glycol (1 µm).

TEMPERATURE

Column 140. Injection port 250. Detector 250.

CARRIER GAS Helium. SPLIT RATIO 10:1.

FLOW RATE 10 mL per minute.

System suitability

SAMPLE Standard preparation.

Suitability requirements

SYMMETRY FACTOR Not more than 2.0 for the menthol peak.

RESOLUTION Not less than 2.0 between the menthol and anethole peaks.

RELATIVE STANDARD DEVIATION Not more than 2.0 per cent for the peak area ratio of menthol to anethole.

COLUMN EFFICIENCY Not less than 2,000 theoretical plates for the menthol peak.

Procedure Separately inject equal volumes (about 2 L) of Standard preparation and Assay preparation into the chromatograph, record the chromatograms, and measure the areas of menthol and anethole peaks. Calculate the areas ratio of menthol to anethole peaks.

Calculation Calculate the content of C₁₀H₂₀O in the portion of the Menthol taken, using the declared content of C₁₀H₂₀O in Menthol RS.