Bo He

MENTHAE HAPLOCALYCIS HERBA (薄荷, Bohe) Peppermint (Fam. Labiatae) The drug is collected in summer and autumn when the foliage branches are growing luxuriantly or during the third round of flowering. It is collected several times on fine days and dried either in the sun or in the shade. Description Stems square, with opposite branches, 15–40 cm long and 2–4 mm in diameter; externally purplish-brown or pale green, the angular regions pubescent; internodes 2–5 cm long; texture fragile; fracture white; pith hollow. Leaves opposite, shortly petiolate; lamina crumpled and rolled. When entire, leaves are broadly lanceolate, long-elliptical or ovate, 2–7 cm long and 1–3 cm wide. The upper surface is dark green and the lower surface greyish-green, sparsely pubescent, bearing concavely dotted glandular scales. Verticillasters axillary; calyx campanulate with five terminal teeth; corolla pale purple. Odour characteristic and aromatic after rubbing; taste pungent and cool. Identification (1) Surface view of the leaf: Glandular scales possess an 8-celled head, up to 90 μm in diameter, with a unicellular stalk. Small glandular hairs consist of a unicellular head and a unicellular stalk. Non-glandular hairs are 1–8 celled, often curved, with thickened and slightly warty walls. Stomata are diacytic and numerous on the lower surface. (2) To the oily matter obtained from the microsublimation of the leaf powder add 2 drops of sulfuric acid and a small quantity of vanillin crystals. A yellow to orange-yellow colour is produced, turning purplish-red after adding one drop of water. (3) To 1 g of the coarse powder add 10 mL of dehydrated ethanol, ultrasonicate for 20 minutes, filter, and use the filtrate as the test solution. Prepare a solution of 1 g of Menthae Haplocalycis Herba Reference Drug in the same manner as the reference drug solution. Dissolve Menthol CRS in dehydrated ethanol to prepare a solution containing 2 mg/mL as the reference solution. Carry out the method for Thin-Layer Chromatography (0502), using silica gel G as the coating substance and a mixture of toluene and ethyl acetate (9:1) as the mobile phase. Apply separately 5–10 μL of each of the above three solutions to the plate. After development, remove the plate and dry it in air. Spray with a mixture of 2% p-dimethylaminobenzaldehyde in 40% sulfuric acid ethanol solution, then heat at 80°C until the bands become distinct. Examine under ultraviolet light at 365 nm. The fluorescent bands in the chromatogram obtained with the test solution correspond in position and colour to those obtained with the reference drug solution and the reference solution. Leaves Not less than 30%. Water Not more than 15.0% (0832, Method 4). Total Ash Not more than 11.0% (2302). Acid-insoluble Ash Not more than 3.0% (2302). Assay Volatile Oil Carry out the method for determination of volatile oil (2204). To a sufficient quantity of 5-mm long sections, add 600 mL of water per 100 g of sample, boil gently for 3 hours, and determine the volatile oil content. It contains not less than 0.80% (mL/g) of volatile oil. Menthol Carry out the method for Gas Chromatography (0521). Chromatographic system and system suitability Use a capillary column (30 m × 0.32 mm × 0.25 μm) with polyethylene glycol (PEG) as the stationary phase. Temperature program: Initial temperature: 70°C, hold for 4 minutes. Increase to 120°C at 1.5°C/min. Increase to 200°C at 3°C/min. Finally increase to 230°C at 30°C/min and hold for 2 minutes. Injector temperature: 200°C Detector temperature: 300°C Split ratio: 5:1 The number of theoretical plates shall not be less than 10,000, calculated with reference to the menthol peak. Processing Remove the old stems and foreign matter, spray with a small quantity of water, soften briefly, cut into short sections, and dry promptly at a low temperature. Description In irregular sections. Stems square, externally purplish-brown or pale green, with longitudinal ridges; the angular regions pubescent. Cut surface white and hollow. Leaves mostly broken; upper surface dark green, lower surface greyish-green, sparsely pubescent. Verticillasters axillary; calyx campanulate with five terminal teeth; corolla pale purple. Odour characteristic and aromatic after rubbing; taste pungent and cool. Identification As required for the crude drug. Water Not more than 13.0%, following the method for the crude drug. Assay Volatile Oil Contains not less than 0.40% (mL/g) of volatile oil, following the method for the crude drug. Menthol Contains not less than 0.13% of menthol (C₁₀H₂₀O), calculated with reference to the dried drug, following the method for the crude drug. Total Ash As required for the crude drug. Acid-insoluble Ash As required for the crude drug. Property and Flavor Cool; pungent. Meridian Tropism Lung and Liver meridians. Actions Disperses wind-heat, clears the head and eyes, benefits the throat, promotes eruption, soothes the liver, and regulates the flow of qi. Indications Wind-heat common cold; the early stage of warm disease; headache; red eyes; sore throat; mouth ulcers; rubella; measles; distention and oppression in the chest and hypochondrium. Administration and Dosage 3–6 g, added near the end of decoction. Storage Preserve in a cool, dry place.