DETECTION OF MENTHA ARVENSIS OIL

10. DETECTION OF MENTHA ARVENSIS OIL

Several color reactions have been proposed to distinguish between the oil distilled from Mentha piperita L. and the oil from Mentha arvensis L.. In common with most color reactions, these tests are not always reliable with mixtures as complex as essential oils.
The test described below is the official test of "The United States Pharmacopoeia."204
Procedure: Mix in a dry test tube 3 drops of oil of peppermint with 5 cc. of a solution of 1 volume of nitric acid in 300 volumes of glacial acetic acid, and place the tube in a beaker of boiling water. In from 1 to 5 min. the liquid develops a blue color which on continued heating deepens and shows a copper colored fluorescence and then fades leaving a golden yellow solution.
The characteristic color changes described in this procedure do not occur if an oil distilled from Mentha arvensis L. is examined : the acid solution then attains a light yellow color which shows no appreciable change during the 5 min. of heating.
It should be remembered that the color changes described are characteristic of the oil from Mentha piperita L. ; mixtures of this oil and Mentha arvensis L. give the color changes described. Therefore, the test cannot be used to detect adulteration with Mentha arvensis L.
Several other color reactions have been described for these oils in the literature.
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204 Eleventh Revision, 259

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