Hey, I'm having a problem isolating a plant extract out of methanol. The solution is about 15% extract by mass. My institute has a rotary vacuum evaporator, however, I have been attempting to use this to no avail and no one here is especially experienced with the apparatus. I really don't know what the problem could be - here's my trouble shooting thus far:

 

• vacuum pressure on the system is 10inhg;
• none or very minimal leaks;
• water bath temp first attempted at 60C won't even evaporate off at 90C;
• tried different speeds of rotations;
• condensor is running.

 

Yesterday it started working for a small period of time, but then I realized that the rotating flask was loose. Once I firmly reattached the methanol stopped evaporating into the condensor. Please help I've tried several other recovery techniques all of which have burned or ruined my extract.

 

 

Are you sure you added methanol? Try evaporating a pure methanol solution and see what happens.

Hey still looking for any help on this final step in my extraction procedure. I've been carrying out the other steps and now just have a lot of methanolic and ethanolic extract waiting to be isolated.

 

2 interesting things I've noticed that might be of help.

 

1) when I increase pressure to above 20inHg the solvent starts to appear in the condensor. this may be a solution to my problem, but the vacuum that I am using is very finicky at this pressure and oscilates between extremely high negative pressure or reverts back to around 10inHg. Is 20inHg an acceptable pressure for a system such as this or am I forcing something that shouldn't be forced?

 

2)when I disconnect the flask with containing the extract forcing a leak between the condensor and the flask the solvent will start evaporating. I don't really know why this is.

 

(and yes I made sure it was methanol and ethanol by weighing the solvents before adding them. Good thought though I wouldn't put it past me.)