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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