I have an oily bacterial cured extracted with DCM. after evaporation of DCM the physical appearance of crude still oily. I tried with DMSO to dissolve the crude and use for AST, but the mixture did not diffuse into the agar and show no any activity as well.
Freeze drying is one of the options was recommended to me. Which I did already after I put my sample in -80 overnight and then placed the sample in freeze dryer for one day at - 100 degree . the sample melt again( return to the normal condition, oily).
any recommendation and advice will be appreciated.
Hi Anmar,
Difficult one - first, you have to be careful of solvents in the freeze dryer as they can damage the oil in the vacuum pump. Second, as you discovered, if you concentrate you can trap solvent in the sample, and can't get it out.
The big question, what is your downstream process? This will determine the best route to take. Routes could include solvent exchange to a more suitable solvent for freeze drying (DMSO is almost impossible to freeze dry well in commercial equipment) or do something else etirely.
There is a good introduction to the basic principles of freeze drying that I have found here:
http://www.spscientific.com/Articles-And-Technical-Papers/
The guy I know who is a great expert at handling such samples is Stephen Pickrahn at TUM in Germany, look for papers by him.
If you need more help, feel free to reach out.
Kind regards,
Rob
Dear Rob.
Thank you for your answer,
First I used Dichloro methane to separate the semi-polar compound from my sample and after evaporation via rotary evaporator to remove the solvent I got this concentrated oil. I tried to dissolve the concentrated oil with DMSO in order to test the bioactivity against bacterial pathogen on agar plate.. but the oil didn't show any result on agar plate as its hard to defuse. so that was my downstream process.
Thank you
Hi Anmar,
In this case I would suggest that you add a higher boiling point solvent (one that is compatible with your screening system) BEFORE you remove the DCM. Essentially you can then fractionally distill things. DMSO would work as it has a high BP.
You could add something like 1,4-Dioxane which doesn't have such a high BP, so you will have to watch the pressure on your evaporator (so as to remove only the DCM) and then you can easily freeze dry from 1,4-Dioxane. You could then dissolve in something friendly to your screening system.
Quite often people that I have encountered doing this work are taking the crude extract and then doing a 2D separation on it to create say 100 fraction that they then individually screen.
Kind regards,
Rob
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