Da Huang - Sheng

RHEI RADIX ET RHIZOMA (大黄, Dahuang) Rhubarb The dried root and rhizome of Rheum palmatum L., Rheum tanguticum Maxim. ex Balf., or Rheum officinale Baill. (Fam. Polygonaceae). The drug is collected in late autumn when the stems and leaves have withered, or in the following spring before sprouting. Rootlets and the outer bark are removed, the drug is cut into pieces or segments, either strung together for drying or dried directly. Description In subcylindrical, conical, ovoid, or irregular pieces, 3–17 cm long and 3–10 cm in diameter. Externally yellowish-brown to reddish-brown after peeling, sometimes with whitish reticulations and scattered star spots (abnormal vascular bundles) visible; occasionally bearing brownish-black patches of cork; mostly with a hole through which a string has passed; and with coarse longitudinal wrinkles. Texture compact, sometimes rather loose and soft in the centre. Fracture pale reddish-brown or yellowish-brown, granular. Pith of the rhizome broad, with star spots arranged in a ring or irregularly scattered. Wood of the root well developed, radially striated; cambium ring distinct; star spots absent. Odour delicately aromatic; taste bitter and slightly astringent, becoming sticky and gritty upon chewing. Identification (1) Microscopic Identification Transverse section Most of the cork and phelloderm of the root removed. In the phloem, sieve tube groups distinct and parenchyma well developed. Cambium forming a ring. Xylem rays relatively dense, 2–4 cells wide, containing brown masses. Vessels unlignified, usually solitary or in small groups, sparsely distributed. Parenchymatous cells containing clusters of calcium oxalate and abundant starch granules. Pith of the rhizome broad, usually with mucilage cavities containing reddish-brown masses. Abnormal vascular bundles scattered. Cambium forming a ring, with xylem outside and phloem inside the cambium. Rays stellately radiating. Powder Yellowish-brown. Clusters of calcium oxalate 20–160 μm in diameter, occasionally up to 190 μm. Bordered-pitted, reticulate, spiral, and annular vessels unlignified. Starch granules abundant; simple granules subspherical or polygonal, 3–45 μm in diameter, with stellate hilum; compound granules composed of 2–8 components. (2) Sublime a small quantity of the powder. Rhombic needle crystals or feathery crystals are visible. (3) Macerate 0.1 g of the powder with 20 ml of methanol for 1 hour and filter. Evaporate 5 ml of the filtrate to dryness. Dissolve the residue in 10 ml of water, add 1 ml of hydrochloric acid, heat under reflux on a water bath for 30 minutes, and cool immediately. Extract with two 20 ml portions of ether. Combine the ether extracts, evaporate to dryness, and dissolve the residue in 1 ml of chloroform as the test solution. Prepare the reference drug solution in the same manner using Rhei Radix et Rhizoma Reference Drug. Dissolve rhein CRS in methanol to produce a solution containing 1 mg/ml as the reference solution. Carry out the method for thin-layer chromatography (0502), using silica gel H mixed with sodium carboxymethylcellulose as the coating substance and the upper layer of a mixture of petroleum ether (30–60°C), ethyl formate, and formic acid (15 : 5 : 1) as the mobile phase. Apply separately 4 μl of each of the above three solutions to the plate. After developing, remove the plate, dry in air, and examine under ultraviolet light at 365 nm. The five orange fluorescent spots in the chromatogram obtained with the test solution correspond in position and colour to those in the chromatogram obtained with the reference drug solution. The orange fluorescent spot in the chromatogram obtained with the test solution corresponds in position and colour to that in the chromatogram obtained with the reference solution. The spot becomes red on exposure to ammonia vapour. Rhaponticin To 0.1 g of the powder add 10 ml of methanol, ultrasonicate for 20 minutes, and filter. Dilute 1 ml of the filtrate to 10 ml with methanol as the test solution. Dissolve rhaponticin CRS in methanol to produce a solution containing 10 μg/ml as the reference solution (prepare freshly before use). Carry out the method for thin-layer chromatography (0502), using polyamide as the coating substance and a mixture of toluene, ethyl formate, acetone, methanol, and formic acid (30 : 5 : 5 : 20 : 0.1) as the mobile phase. Apply separately 5 μl of each solution to the plate. After developing, remove the plate, dry in air, and examine under ultraviolet light at 365 nm. The bright blue fluorescent spot in the chromatogram obtained with the test solution should not correspond in position and colour to the spot in the chromatogram obtained with the reference solution. Water Not more than 15.0% (0832, Method 2). Total Ash Not more than 10.0% (2302). Acid-insoluble Ash Not more than 2.0% (2302). Extractives Carry out the hot extraction method for the determination of ethanol-soluble extractives (2201), using 70% ethanol as the solvent; not less than 22.0%. Assay Carry out the method for high-performance liquid chromatography (0512). Chromatographic System and System Suitability Use octadecylsilane-bonded silica gel as the stationary phase and a mixture of methanol and water (15 : 85) as the mobile phase. The detection wavelength is 275 nm. The number of theoretical plates of the column is not less than 2000, calculated with reference to the peak of salidroside. Reference Solution Dissolve salidroside CRS, accurately weighed, in methanol to produce a solution containing 0.5 mg/ml. Test Solution Accurately weigh 0.5 g of the powder (through No. 3 sieve) into a stoppered conical flask. Accurately add 10 ml of methanol and weigh. Ultrasonicate for 30 minutes, cool, weigh again, replenish the loss in weight with methanol, mix well, filter, and use the subsequent filtrate as the test solution. Procedure Inject accurately 10 μl each of the reference solution and the test solution into the chromatograph, and calculate the content. It contains not less than 0.50% of salidroside (C14H20O7), calculated with reference to the dried drug. Prepared Slices Processing Remove the fibrous roots, eliminate foreign matter, cut into slices, and dry. Description Rounded, subrounded, or irregular slices. Externally brown, reddish-brown, or dark brown, some bearing a layer of yellow membranous epidermis with a cerise decorative pattern after removal of the outer epidermis. Cut surface cerise to purplish-red, sometimes with fissures. Texture light and lax. Odour aromatic; taste initially slightly bitter and astringent, then sweet. Extractives Carry out the method for determination of water-soluble extractives (2201, hot extraction method). It contains not less than 25.0%. Assay Total Anthraquinone Carry out the method for high-performance liquid chromatography (0512). Chromatographic System and System Suitability Use octadecylsilane-bonded silica gel as the stationary phase and a mixture of methanol and 0.1% phosphoric acid (85 : 15) as the mobile phase. Detection wavelength: 254 nm. The number of theoretical plates is not less than 3000, calculated with reference to the peak of emodin. Reference Solution Accurately weigh aloe-emodin CRS, rhein CRS, emodin CRS, chrysophanol CRS, and physcion CRS, respectively. Prepare stock solutions in methanol containing: Aloe-emodin: 80 μg/ml Rhein: 80 μg/ml Emodin: 80 μg/ml Chrysophanol: 80 μg/ml Physcion: 40 μg/ml Accurately measure 2 ml of each stock solution and mix to obtain a reference solution containing: Aloe-emodin: 16 μg/ml Rhein: 16 μg/ml Emodin: 16 μg/ml Chrysophanol: 16 μg/ml Physcion: 8 μg/ml Test Solution Accurately weigh 0.15 g of the powder (through No. 4 sieve) into a stoppered conical flask. Accurately add 25 ml of methanol and weigh. Heat under reflux on a water bath for 1 hour, cool, weigh again, replenish the loss of solvent with methanol, mix well, and filter. Accurately measure 5 ml of the subsequent filtrate into a flask and evaporate to dryness. Add 10 ml of 8% hydrochloric acid, ultrasonicate for 2 minutes, then add 10 ml chloroform. Heat under reflux for 1 hour, cool, and transfer to a separating funnel. Wash the flask with a small quantity of chloroform and combine the washings. Separate the chloroform layer. Extract the aqueous layer with three 10 ml portions of chloroform. Combine the chloroform extracts and evaporate to dryness under reduced pressure. Dissolve the residue in methanol, transfer to a 10 ml volumetric flask, dilute to volume with methanol, and mix well. Procedure Inject accurately 10 μl each of the reference solution and the test solution. Calculate the content. It contains not less than 1.5% of the total amount of aloe-emodin (C15H10O5), rhein (C15H8O6), emodin (C15H10O5), chrysophanol (C15H10O4), and physcion (C16H12O5), calculated with reference to the dried drug. Free Anthraquinone Carry out the method for high-performance liquid chromatography (0512). Chromatographic System and System Suitability As described under Total Anthraquinone. Reference Solution As described under Total Anthraquinone. Test Solution Accurately weigh 0.5 g of the powder (through No. 4 sieve) into a stoppered conical flask. Add accurately 25 ml of methanol and weigh. Heat under reflux on a water bath for 1 hour, cool, weigh again, replenish the loss of solvent with methanol, mix well, filter, and use the subsequent filtrate as the test solution. Procedure Inject accurately 10 μl each of the reference solution and the test solution. Calculate the content. It contains not less than 0.20% of the total amount of aloe-emodin, rhein, emodin, chrysophanol, and physcion, calculated with reference to the dried drug. Assay For the prepared slices: Total Anthraquinone As required for the crude drug. Free Anthraquinone Not less than 0.35%, following the method described for the crude drug.