【Description】This product is a light yellow to brownish-yellow powder; odorless, bitter taste. It is soluble in boiling ethanol, slightly soluble in methanol or ethanol, and almost insoluble in water. The melting point should be 224–230°C, with decomposition upon melting (General Rule 0612).   【Identification】(1) Dissolve about 10 mg of the product in 2 ml of ethanol, add 2 drops each of a 2% ethanolic solution of 3,5-dinitrobenzoic acid and a 5% ethanolic solution of potassium hydroxide, shake well, and a purplish-red color develops.   (2) Dissolve about 10 mg of the product in 2 ml of ethanol, add 2–3 drops of ethanolic potassium hydroxide solution, and a red color gradually develops, turning yellow upon standing.   (3) Prepare a solution of the product in anhydrous ethanol containing 10 μg per ml. Determine by ultraviolet-visible spectrophotometry (General Rule 0401), and a maximum absorption is observed at a wavelength of 224 nm.   【Tests】Other lactones Prepare a solution of the product in anhydrous ethanol containing 2 mg per ml as the test solution. Carry out the test by thin-layer chromatography (General Rule 0502). Apply 10 μl of the above solution to a silica gel G thin-layer plate, using chloroform-methanol (19:1) as the developing agent. After development, remove the plate, air-dry, and spray with an equal-volume mixture of a 2% ethanolic solution of 3,5-dinitrobenzoic acid and a 5% ethanolic solution of potassium hydroxide (prepared before use). In the chromatogram of the test solution, no spots other than the principal spot should appear.  Loss on drying When dried to constant weight at 105°C, the loss in weight is not more than 1.0% (General Rule 0831).   Residue on ignition Not more than 0.1% (General Rule 0841).   【Assay】Determine by high-performance liquid chromatography (General Rule 0512). Chromatographic conditions and system suitability test Use octadecylsilane-bonded silica gel as the filler; methanol-water (60:40) as the mobile phase; detection wavelength is 225 nm. The number of theoretical plates calculated for the andrographolide peak should not be less than 5000. Preparation of reference solution Accurately weigh an appropriate amount of andrographolide reference substance, add methanol to prepare a solution containing 0.1 mg per ml. Preparation of test solution Accurately weigh about 25 mg of the product, place in a 50 ml volumetric flask, dissolve with methanol and dilute to volume, mix well. Accurately transfer 5 ml to a 25 ml volumetric flask, dilute with methanol to volume, mix well. Procedure Accurately inject 10 μl each of the reference solution and the test solution into the liquid chromatograph, and determine. Calculated on the dried basis, the content of andrographolide (C20H30O5) should be 95.0%–101.0%. 【Storage】Protect from light, keep tightly closed.