Dear Sagar,

Thank you for your question as expert in flavonoisd analysis. The best solvent is methanol and not aqueous methanol. For more details please find my publication attached.

Best regards

Aly

Thesis Chapter 2-TO INVESTIGATE THE ANTIOXIDANT PROPERTIES OF DIETA...

Dear Aly,

Thank you very much for your answer.

I had used 80% ethanol as a solvent. The solubility of quercetin is reported to be 21mg/ml at 25 degree celcius in ethanol. I was preparing 20 mg/ml, but it didn't get soluble. Can you explain what may be the possible problem here?

Also, what is the solubility of Quercetin in absolute methanol? Absolute Methanol evaporates very fast. In such case, is this solvent suitable for making stock solution of quercetin (20 mg/ml)?

Thank you for your help.

From my experience, quercetin is hardly soluble at this concentration. I usally dissolve 10 mg in 10 mL MeOH as a stock solution for HPLC standards. Yet, I always have to place it in an ultrasonic bath for at least 30min to get is dissolved.

In 80% EtOH the solubility is even worse. I don't know where you got the solubility data (21 mg/mL) from, but I cannot confirm this value.

When possible try to stick to pure MeOH or MeCN, which is even better. Also keep the pH of the solution below 3 to avoid oxidative deterioration of the quercetin.

http://www.scbt.com/datasheet-203225-quercetin-dihydrate.html

I got solubility data from above link.

How about heating pure MeOH solution? Does heating solve this problem?

Heating will always help, yet I would not go > 40°C to avoid thermal decomposition of the compound.

Re solubility in EtOH/MeOH you might also check this publication:

Article Solubility of Quercetin in Water + Methanol and Water + Etha...

From my experience, solution (1 mg/ml as stock solution) in pure MeOH works best. Ultrasonication for 5 min will help the dissolution yet the duration is depending on your concentration - the higher concentration, the longer time for sonication. You may try to prepare your stock solution from the smallest amount of quercetin you can accurately weight in order to improve the solubility.

You may use absolute ethanol and it will be soluble. However, 70-80% solution is preferred because the partial solubility coefficient in ethanol and water plays a vital role in many reaction.

Thank you so much, currently am extracting quercetin from onions and apples. This information is much more helpful.

I would also like to know what methods except HPLC can I use to quantify it.

Hi all,

I have seen different values for Quercetin solubility in Ethanol in different references (from 2 to 25 mg/ml).

I highly appreciate it if someone can share an authentic reference that we can use in our work? To avoid trouble later during publication.

Thanks in advance.