Oleum menthaeIt is a volatile oil obtained from fresh stems and leaves of peppermint in the labiaceae family by steam distillation, refreezing and partial brain removal。

 Peppermint oil is a clear liquid that is colorless or light yellow。

 Has a special cool aroma, taste first hot, after cool。Aged for a long time, gradually darker color。
 Peppermint oil can be mixed with ethanol, chloroform or ether。

Relative density: should be 0.888～0.908 (Appendix VII A)。
Optical rotation: Take this product, place it in a 1dm tube, and determine (Appendix Ⅶ E) according to law as -17° ~ -24°。
Refractive index:

 应为1.456～1.466 (Appendix VII F)。

 Take 1 drop of peppermint oil, add 3 to 5 drops of sulfuric acid and a small amount of vanillin crystal, should show orange-red, then add 1 drop of water, that is, turn purple。

颜色：

Take peppermint oil and the same volume of yellow No. 6 standard color comparison solution, not deeper。
Insoluble substances in ethanol:
Take 1ml peppermint oil and add 70% ethanol 3.5ml, the solution should be clarified。
Heavy metals:

Take 1g peppermint oil, check according to law (Appendix IX E 2 method), containing heavy metals shall not exceed 10 parts per million。

Ester content:

Take about 5 peppermint oil, accurately weigh it, put it in a flask, add 10ml of neutral ethanol (the phenolphthalein indicator liquid is neutral), mix it, add 2 drops of phenolphthalein indicator liquid, and first use ethanol to produce potassium hydroxide titrant (0.1mol/L) neutralize the free acid, and then precisely add ethanol to produce potassium hydroxide titrant (0.5mol/L)25ml, put in a water bath for 1 hour, cool, and then add phenolphthalein indicator liquid 0.5ml, with hydrochloric acid titrant (0.5mol/L) titrate the remaining potassium hydroxide and make a blank test at the same time。
For every 1ml of ethanol to potassium hydroxide titrant (0.5 moles per liter is equal to 99.15mg of C12H22O2。

 Peppermint oil acetate (C12H22O2) is calculated as 2.0～6.5％(g/g) 。
Total alcohol content:

(1) Acetylation: TakeOleum menthaePlace 0ml in an acetylation bottle, add 10ml of acetic anhydride and 2g of newly melted anhydrous sodium acetate, attach an air return condensing tube, heat in an oil bath at 145±3℃ for 75 minutes, remove and cool, add 50ml of water, place in a water bath, shake frequently, heat for 15 minutes, and cool。
Remove the acid in the lower layer by moving the separator funnel。
The remaining acetylated oil was washed with sodium chloride saturated solution, sodium chloride saturated solution saturated with sodium carbonate and sodium chloride saturated solution one by one, each time about 50ml, and then washed with water, about 50ml each time, until the lotion was neutral to the phenolphthalein indicator solution。
Put the obtained acetylated oil into a 25ml flask, add anhydrous sodium sulfate 3g, plug it, and shake it constantly to dehydrate, until 1 drop of acetylated oil is added to 10 drops of carbon disulfide, and then filter it with dry filter paper。
(2) saponification: Take dry acetylated oil about 2.5g, precision weighing, placed in 250ml conical bottle, precision added ethanol to produce potassium hydroxide titrant (0.5mol/L)50ml, according to the ester content measurement item, from "after 1 hour of reflux on the water bath", according to the law, with acetylated oil to consume hydrochloric acid titrant (0.5mol/L) amount (ml) as A, blank consumption of hydrochloric titrant (0.5mol/L) quantity (ml) as B, calculated according to the following formula, is obtained。

　　　　　　　(B-A)×0.07　　　　　　　　　　815
E Total alcohol content % = ────× (1-0.2119×── × 100% W-(B-A) ×0.02
　　　　　　　　　　102　　　　　　　　　　　　100

式中
W is the weight of the acetylated oil (g);E is the ester content of the test product。
The total alcohol content of this product is calculated according to menthol (C10H20O) and shall not be less than 50.0％(g/g) 。

(The above content is from Baidu Search。）