» Peppermint Oil is the volatile oil distilled with steam from the fresh overground parts of the flowering plant of Mentha piperita Linné (Fam. Labiatae), rectified by distillation and neither partially nor wholly dementholized. It yields not less than 5.0 percent of esters, calculated as menthyl acetate (C12H22O2), and not less than 50.0 percent of total menthol (C10H20O), free and as esters.
Packaging and storage Preserve in tight containers, and prevent exposure to excessive heat.
Solubility in 70 percent alcohol One volume dissolves in 3 volumes of 70 percent alcohol, with not more than slight opalescence.
Identification Mix in a dry test tube 6 drops of Oil with 5 mL of a 1 in 300 solution of nitric acid in glacial acetic acid, and place the tube in a beaker of boiling water: within 5 minutes 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.
Specific gravity 841: between 0.896 and 0.908.
Angular rotation 781A: between 18 and 32.
Refractive index 831: between 1.459 and 1.465 at 20.
Heavy metals, Method II 231: 20 µg per g.
Limit of dimethyl sulfide Distill 1 mL from 25 mL of Oil, and carefully superimpose the distillate on 5 mL of mercuric chloride TS in a test tube: a white film does not form at the zone of contact within 1 minute.
Assay for total esters Place about 10 g of Oil, accurately weighed, in a 250-mL conical flask, add 10 mL of neutralized alcohol and 2 drops of phenolphthalein TS, then add, dropwise, 0.1 N sodium hydroxide until a faint pink color appears. Add 25.0 mL of 0.5 N alcoholic potassium hydroxide VS, connect the flask to a reflux condenser, and heat on a boiling water bath for 1 hour. Allow the mixture to cool, add 20 mL of water, add phenolphthalein TS, and titrate the excess alkali with 0.5 N hydrochloric acid VS. Perform a blank determination, disregarding the 0.1 N sodium hydroxide (see Residual Titrations under Titrimetry 541). Each mL of 0.5000 N alcoholic potassium hydroxide consumed in the saponification is equivalent to 99.15 mg of total esters calculated as menthyl acetate (C12H22O2).
Assay for total menthol Place 10 mL of Oil in an acetylation flask of 100-mL capacity, and add 10 mL of acetic anhydride and 1 g of anhydrous sodium acetate. Boil the mixture gently for 1 hour, accurately timed, cool, disconnect the flask from the condenser, transfer the mixture to a small separator, rinsing the acetylation flask with three 5-mL portions of warm water, and add the rinsings to the separator. When the liquids have completely separated, discard the water layer, and wash the remaining oil with successive portions of sodium carbonate TS, diluted with an equal volume of water, until the last washing is alkaline to phenolphthalein TS. Dry the resulting oil with anhydrous sodium sulfate, and filter. Transfer 5 mL of the dry acetylated oil to a tared, 100-mL conical flask, and weigh. Add 50.0 mL of 0.5 N alcoholic potassium hydroxide VS, connect the flask to a reflux condenser, and boil the mixture on a steam bath for 1 hour, accurately timed. Allow the mixture to cool, add 10 drops of phenolphthalein TS, and titrate the excess alkali with 0.5 N hydrochloric acid VS. Perform a blank determination (see Residual Titrations under Titrimetry 541). Calculate the percentage of total menthol in the Oil tested by the formula:
7.813A(1 0.0021E) / (B 0.021A)in which A is the result obtained by subtracting the number of mL of 0.5 N hydrochloric acid required in the above titration from the number of mL of 0.5 N hydrochloric acid required in the residual titration blank, E is the percentage of esters calculated as menthyl acetate (C12H22O2), and B is the weight of acetylated oil taken.
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USP32NF27 Page 1298
Chromatographic columns text is not derived from, and not part of, USP 32 or NF 27.