I'm currently doing plant and spice extractions (Neem leaves, Black pepper, Illicium verum) by using Soxhlet, solvent used are ethyl acetate, absolute ethanol, and hexane/petroleum ether. Aim to determine the larvicidal effects of these extracts.
However, after I Soxhlet, rotary evaporated, then freeze-dried, the extracts (using ethyl acetate) still remain sticky. I tried freeze-drying for twice but it didn't works.
I only done the extraction using ethyl acetate, so for other solvents, I'm not sure whether I'll encounter this problem or not. It is possible?
Is there any solution to change these sticky extracts to powder?
*I want it to be powder form because I need to know the weight after extraction, in order to calculate the concentration and perform subsequent dilutions from it.
Dear Seow,
The organic solvents that you used are very difficult to freeze dry which means you get the result you have. Dissolve your extracts in water or a mixture of water and something organic that can freeze dry, e.g. 1,4-dioxane or tertirary butanol (you can use these 100% also) or possibly even cyclohexane 100%.
Freeze them, and place in the dryer - you should then get a powder result.
Kind regards
Rob
Dear Rob Darrington ,
Thank you for your suggestion. However, I try to avoid using water in my extracts as I'll be performing GC-MS analysis on my extracts afterwards.
Do you mean I need to change my current solvent to 1,4-dioxane/tertiary butanol? Or I add some of these to my current extracts? If it is so, is it necessary to rotary evaporate before freeze-dry?
Dear Seow,
Ethyl Acetate, acetate and hexane will not freeze in the freeze dryer (not using any regular lab system). If they do not freeze, the system will only work like any other concentrator ... a rotovap or Genevac type system. To get good freezing then you need to use a different solvent, such as 1,4-dioxane, tertiary butanol or cyclohexane - this needs be chosen based on what works well for your extracts. Please note that you need to make sure that the freeze dryer is suitable for working with the solvents you are using.
For a general guide to freeze drying, look here:
https://www.spscientific.com/freeze-drying-lyophilization-basics/
For some papers on working with natural products extracts, look here:
https://www.spscientific.com/ContentBlock.aspx?id=3317
You will need to register to access the downloads.
Kind regards,
Rob
- Badges
- Science topic