[3dem] Ethane - propane mix

[Cedric Bouchet-Marquis]

When you remove the grid from the mix, check between your tweezers if any solvent remain. Most of the time going very slowly when removing the grid out of the solvent is enough get rid of it (let the grid hang half in half out the mix for a couple of seconds). Then you should be able to go straight to the TEM with less chance of crashing the vacuum.

Cedric

-----Original Message-----
From: 3dem-bounces at ncmir.ucsd.edu [mailto:3dem-bounces at ncmir.ucsd.edu] On Behalf Of benoit.zuber at ana.unibe.ch
Sent: Tuesday, May 01, 2012 3:30 PM
To: rice at nysbc.org
Cc: 3dem at ncmir.ucsd.edu
Subject: Re: [3dem] Ethane - propane mix

Dear Bill,

I have made the same experience with pure ethane. If I go straight from the plunger to the EM, I have a vacuum crash nearly every time. Two solutions:
1. Leave the grid in LN2 overnight. Eventually the frozen solvent sublimates. 
Or
2. Melt the solvent (in your case it is probably already liquid) by raising the grid above liquid nitrogen and leaving it in cold vapours of nitrogen for a few seconds. Blot off the liquid solvent with a piece of blotting paper. If you are scared you can pre-chill the paper by dipping it in LN2 and letting then LN2 evaporate. I found this step is unnecessary. Immediately after blotting, plunge the grid in LN2 again. This is mainly to prevent ice contamination. Temperature is rather cold in the vapours so devitrification is normally not an issue unless you spend minutes there. If in doubt use a thermocouple to check the temperature in the vapours. Of course the work environment should be free of strong air stream to prevent blowing away the cold layer of nitrogen vapours. 

Hope it helps
Ben

Le 1 mai 2012 à 22:03, "William Rice" <rice at nysbc.org> a écrit :

Dear all,

Have many of you had experience using a mix of 37% ethane / 63% propane as a cryogen? It has the advantage that it stays liquid at liquid nitrogen temperature. We had thought it would be easier to handle, but we found that it seems to leave a thin layer of liquid cryogen on the surface of the grid. Putting a freshly frozen grid into the microscope seemed to cause problems with the IGP as this liquid seemed to evaporate only in the high vacuum of the microscope. Solid ethane frozen on the grid usually cracks and breaks off or sublimes in the airlock during pumping before insertion. Has anyone else seen this effect?

Thanks,
Bill

-- 
William J. Rice, Ph.D.
Senior Scientist
New York Structural Biology Center
89 Convent Avenue, NY, NY 10027


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