Menthol Identification by TLC

Identification and analysis of menthol or identification test for menthol, Determination of menthol in oil of peppermint by TLC. 

Significant hazard of Menthol

Acetone is Highly flammable. Irritant vapor.

Anisaldehyde solution Irritant vapour. Flammable

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Dinitrobenxoyl chloride soln Flammable. Corrosive. Harmful

Ethyl acetate Toxic. Irritant. Highly flammable.

Menthol Irritant.

Methanol Toxic. Highly flammable. Irritant

Pyridine is Highly flammable. Harmful. Suspected carcinogen.

Toluene Suspected teratogen. Irritant vapor. Harmful. Highly flammable

Refer to individual safety data sheets and SOPA18/SOPA38 for further information.

Method

Solution S:

Dissolve 2.50 g of sample in 10 ml of ethanol (96%) and dilute to 25.0 ml with the same solvent. Carry out either tests A & B or test C & D:

A. The sample complies with the test for specific optical rotation.

B. Examine the chromatograms obtained in the test for related substances.

The principal peak in the chromatogram obtained with test solution (b) is similar in position and approximate dimensions to the principal peak in the chromatogram obtained with reference solution (c).

Menthol Identification by TLC:

Test solution of menthol

Dissolve 25 mg of the substance to be examined in methanol R and dilute to 5 ml with the same solvent.

Reference solution for menthol

Dissolve 25 mg of menthol CRS in methanol R and dilute to 5 ml with the same solvent.

Apply separately to the plate 2 μl of each solution. Develop over a path of 15 cm using a mixture of 5 volumes of ethyl acetate R and 95 volumes of toluene R. Allow the plate to dry in the air until the solvents have evaporated and spray with anisaldehyde solution. Heat from 100°C to 105°C for 5 min to 10 min.

The principal spot in the chromatogram obtained with the test solution is similar in position, color, and size to the principal spot in the chromatogram obtained with the reference solution.

D. Dissolve 0.20 g in 0.5 ml of anhydrous pyridine R. Add 3 ml of a 150 g/l solution of dinitrobenzoyl chloride R in anhydrous pyridine R.

Heat on a water bath for 10 min. Add 7.0 ml of water R in small quantities with stirring and allow to stand in iced water for 30 min. A precipitate is formed. Allow to stand and decant the supernatant liquid.

Wash the precipitate with two quantities, each of 5 ml, of iced water R, recrystallize from 10 ml of acetone R, wash with iced acetone R, and dry at 75 °C at a pressure not exceeding 2.7 kPa for 30 min.

Determine the melting point of the resultant crystals.

The crystals melt at 154°C to 157°C.

Residue on an evaporation test method for Menthol

Weigh accurately about 2g of sample into a tared open dish, and heat on a water bath until the bulk of the sample has evaporated.

Transfer the dish to an oven at 100 - 105°C and heat for 1 hour. Express the weight of residue as a percentage of the weight taken.