To any new compound for screening of yield or purity, need to go for higher to lower polarity, eg- Petroleum ether, hexane, acetone... methanol, ethanol and water. In this process can expect your yield. Later combination of solvents through separation method to get some isolated compounds. Refer some relevant article. Good luck

Its already obtained using ethyl acetate. So what next to increase the purity?

I'd try an ion exchange column. I've been successful purifying acidic plant extracts with a SAX (strong anion exchange) column, and this looks like a good candidate for this purification.

The basic procedure is to dissolve the extract in methanol containing some ammonium hydroxide, filter if needed (to remove neutral or basic non-polar compounds that aren't dissolved), load on the column, wash with methanol (plain methanol), then elute with acidic water (acetic or formic acid). Depending on the column, it may need to be conditioned prior to use with an appropriate ion (acetate, in my case). The columns I used were packed containing a chloride counter-ion and the weak organic acids couldn't displace this ion.

See the flowing links for more details and hints:

http://www.isco.com/WebProductFiles/Applications/101/Application_Notes/AN87_RediSep%20Rf_SAX_Column_Applications.pdf

http://www.isco.com/WebProductFiles/Applications/101/Application_Notes/AN98_Hints%20for%20Strong%20Ion%20Exchange%20Resins.pdf

http://www.isco.com/WebProductFiles/Applications/101/Poster_and_Paper_Reprints/Purification_of_Phenolic_Flavonoids.pdf

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