5 replies to this topic

[shimshady]

How do you guys do it?

[mdfenko]

do you have the apparatus?

what volume are you talking about?

[shimshady]

no real apparatus but im talking like 30-60 mL.  However we do have everything to do it without one, im more just concerned with the temp at which you do it, any suggestions how to freeze it.  Do you keep it frozen the whole time?  THings like that.

Edited by shimshady, 29 May 2009 - 10:34 AM.

[mdfenko]

we would shell freeze the solution, in a round flask, using a dry ice/acetone bath to freeze the solution. the same dry ice/acetone bath would be placed between the vacuum pump and the sample as a condensing vessel.

you pull a strong vacuum and let it go. the frozen sample will not defrost as long as it doesn't touch a (warm) surface.

when it is fully dry, scrape the powder out of the flask and store it in a vial or you can just seal the flask and store.

i think i covered just about everything (i haven't done this for a long time so forgive me if i left anything out), if not then ask.

[shimshady]

That is exactly what i was looking for.  Thanks.  My next question is about how long does it take?  i know it differs depending on volume but do you let it go overnight?   Im looking at aorund 30-60 mL.

[mdfenko]

if memory serves me correctly (it's been many, many moons since i did this), we mostly let it go overnight. we occasionally completed it during the day (if we started early enough). sometimes it had to go more than overnight.

time to dry is very dependent upon the strength of the vacuum that you pull as well as the starting volume.