Edition: BP 2025 (Ph. Eur. 11.6 update)
General Notices
Menthol in Aqueous Cream
NOTE: This monograph has been developed to cover unlicensed formulations.
DEFINITION
Levomenthol Cream contains Levomenthol in Aqueous Cream.
The cream complies with the requirements stated under Topical Semi-solid Preparations and with the following requirements. Where appropriate, the cream also complies with the requirements stated under Unlicensed Medicines.
Content of levomenthol, C10H20O
90.0 to 110.0% of the stated amount.
IDENTIFICATION
In the Assay, the chromatogram obtained with solution (2) shows a peak with the same retention time as the peak due to levomenthol in the chromatogram obtained with solution (3).
ASSAY
Carry out the method for gas chromatography, Appendix III B, using the following freshly prepared solutions.
(1) 0.1% w/v of camphor (internal standard) in industrial methylated spirit (95%).
(2) Disperse a quantity of the well-mixed cream containing 50 mg of Levomenthol in 20 mL of industrial methylated spirit (95%) and mix with the aid of ultrasound for 15 minutes. Transfer the liquid contents to a 50 mL graduated flask, rinse the original flask with two 10-mL quantities of industrial methylated spirit (95%), transfer the washings to the graduated flask and add sufficient industrial methylated spirit (95%) to produce 50 mL; mix well and filter (Whatman No. 1 paper is suitable) discarding the first 5 mL of filtrate. Add 10 mL of solution (1) to 10 mL of the filtrate and add sufficient industrial methylated spirit (95%) to produce 25 mL; mix well.
(3) Mix 5 mL of a 0.2% w/v solution of levomenthol BPCRS in industrial methylated spirit (95%) with 10 mL of solution (1) and dilute to 25 mL with industrial methylated spirit (95%).
CHROMATOGRAPHIC CONDITIONS
(a) Use a fused silica column (10 m × 0.53 mm) bonded with a 0.25-μm layer of dimethylpolysiloxane.
(b) Use helium as the carrier gas.
(c) Use the gradient conditions described below.
(d) Use an inlet temperature of 250°.
(e) Use a flame ionisation detector at a temperature of 250°.
(f) Inject 1 μL of each solution.
| Time (Minutes) | Temperature | Comment |
| 0->1 | 90° | isothermal |
| 1->5 | 90° -> 230° | linear gradient |
| 5->9 | 230° | isothermal |
When the chromatograms are recorded under the prescribed conditions the retention times are: levomenthol, about 2.1 minutes; camphor, about 2 minutes.
DETERMINATION OF CONTENT
Calculate the content of C10H20O in the cream using the declared content of C10H20O in levomenthol BPCRS.
