[Description] This product is a colorless crystalline powder; odorless, with a 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 test 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. According to the ultraviolet-visible spectrophotometry method (General Rule 0401), determine the absorption, and a maximum absorption should occur at a wavelength of 224 nm. 

 [Test] Other lactones: Prepare a test solution of the product in anhydrous ethanol containing 2 mg per ml. 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 a mixture of chloroform-methanol (19:1) as the developing solvent. After development, remove the plate, air-dry, and spray with a freshly prepared equal-volume mixture of a 2% ethanolic solution of 3,5-dinitrobenzoic acid and a 5% ethanolic solution of potassium hydroxide. In the chromatogram of the test solution, no spots other than the principal spot should appear.

 Loss on drying: Dry the product at 105°C to constant weight; the loss in weight should not exceed 1.0% (General Rule 0831). 

 Residue on ignition: Should not exceed 0.1% (General Rule 0841). 

 [Assay] Determine by high-performance liquid chromatography (General Rule 0512). Chromatographic conditions and system suitability: Use octadecylsilane-bonded silica gel as the filler; a mixture of methanol-water (60:40) as the mobile phase; and a detection wavelength of 225 nm. The number of theoretical plates calculated for the andrographolide peak should be not less than 5000. Preparation of reference solution: Accurately weigh an appropriate amount of andrographolide reference standard, 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 measure 5 ml, place in a 25 ml volumetric flask, dilute with methanol to volume, mix well. Assay 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.