Dear Scientists,
I am confused now. I did extraction from plant with 90 percent ethanol at 40 degree centigrade in reflux condensor, then i evaporated the ethanol in evaporator and also in vaccum oven. Now i want to do lyophilization and for that i have to freeze the samples. Since 2 days i am trying to freeze them at minus 20 degree centigrade but its not working. Can any one tell me as what to do now? What can be the mistakes if i have done any?
Hello, As I see by your described procedure you evaporate all humidity and volatile compounds from sample, so what you have in final for freezing at -20oC? Lyophilization means evaporation from solid condition avoiding liquid condition. So if you want to have liophilized sample you do not need to completely dry sample at first. Just use the vacuum to remove the alcohol then add little bit water or other liquid that you prefer which can freeze at -20. Freeze the samples and then you can perform lyophilization.
Sir, thanks for ur kind answer. But I still have the samples in liquid form. Because i used 90 percent aquous ethano. Now when i store them under minus 20 , then still they dont freeze. This is what made me confused..
The concentration of your solute is depressing the freezing point of your sample. Too freeze dry you need to add water. This is counter-intuitive, but this is the reason the sample will not freeze. When you add water, you need to throughly mix the sample also. Darbinyan is correct that you can use the deep vacuum of a freeze dryer to freeze a dilute sample, but this will not work with the sample in the current state.
Kind regards
Rob
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