Method for preparing baicalin standard

Baicalin refinement: take the crude Astragalus membranaceus, add 10 times the amount of water to make it a suspension, add 40% NaOH to pH=7.5 when heated to 80 °C, make it fully soluble, then adjust the ph=6.5 with Hcl. 95% ethanol gave an alcohol content of 60%, and a reddish brown floc was produced, which was then removed by filtration. Then adjust the pH=2, and then leave it to be completely precipitated to obtain the yellow baicalin product (melting point 212 ° C - 215 ° C, which is the standard for the current application).

Re-refining of baicalin: Take a certain amount of refined product, add the total amount (1:250) of methanol in the reflux extractor, heat and reflux for 15 minutes, and heat-filter. The precipitate was combined with the undissolved portion and heated to reflux with methanol. This is done step by step until the refined product is dissolved. Each time the filtrate is concentrated with the reduced pressure to 2/5 of the original volume, rapidly cooled, precipitated crystals, placed for about half an hour to filter, washed with methanol: crystallized below 60 ° C: so recrystallized 2-3 times A standard product of light yellow fine needle crystals (melting point 223 ° C - 224 ° C) can be obtained.

Melting point 223-225 ° C, [α] 18D + 123 ° C (c = 0.2, pyridine-water); soluble in N, N-dimethylformamide , pyridine, soluble in sodium bicarbonate, sodium carbonate, hydrogen Alkaline solution such as sodium oxide, but unstable in lye, gradually dark brown, slightly soluble in hot glacial acetic acid, insoluble in formic acid, acetic acid, acetone, almost insoluble in water, ether, benzene, chloroform, etc.