Hello Iylia

Water is notoriously difficult to evaporate with a Rotovap, you won't get around using much higher temperatures (>=60C) for long times. May I suggest two different approaches:

1) carefully boil the extract down in a beaker, if you expect the tannins to be relatively heat stable, then transfer to the rotovap

2) or preferrably, use freeze-drying. much simpler, much more gentle, still takes a couple hours but it's a lot safer.

If I increase the temperature of water bath to 80C. Will it affect the bioactive compounds in the extract? Will the compounds be denatured? I've managed to remove the water out at 80C but I am concerned about the degradation of bioactive compounds in the extract. What do you think? 

Well, as my former supervisor would tell me: "You're the clever student, find it out. We're scientists, we do experiments".

Whether the compounds will denature obviously depends on the compounds (of course, no idea what exactly is in your extract), but AFAIK tannins are quite hardy. You won't find out unless you try.

Alternatively, next time, if possible, use a more volatile solvent (Acetone, Methanol, Ethyl Acetate, ...)

Dear Researcher

There is a way to solve this problem. Add 2 volume of acetone in your solution , now boiling point of final solution will lower .Pour this solution in to your appratus and distille it under vaccume. This is my own experience, only you can  distille out small fractions in this way but by repeating procedure you can achive your goal. May be some precipitaion occure after addition of acetone but that ppt are tannins. Good Luck

I see. Thank you  guys =) 

Dear Zaki

Add ethanol to your aqueous extract. Water and ethanol form an azeotropic mixture that boil easily at 40-50°C under a vaccum of 70-80 mPa.

Regards!

NOBOSSE.

If your extract volume is approx. 50 ml, then you can remove water by freeze drying process. This is the best way to remove water without decomposition.

Or otherwise you can remove on rota vapor by changing temp./ vacuum with respect to nature of your sample.. During concentration, you should take care during concentration on rotavapour. You can not leave it because your sample may suck back due to high vacuum.       

Dear Zaki

I agree that the better option is to freeze-dry your sample, always keep in mind that your compounds are labile to high temperatures. 

Also you can use a mixture of 1 volume of BuOH and evaporate below 60 mPa at 40-45ºC as was mentioned.

regards

FR

Thanks.

freeze dryer is the option and next time you are using water as your extraction solvent i suggest you use freeze dryer.

You can also add n-butanol for easy evaporation

Increase the temp to 50 or 60 degree C.

it is better to extract tannins with aqueous alcohol or aqueous acetone

Good answer and thanks.