[3dem] Ethane - propane mix

Thu May 3 11:57:25 PDT 2012

We pump for 90 seconds on our F20 (turbo). This solved any problems with vacuum "burps" and usually no contamination of ethane is evident on the grids, even when looking at the specimens on the same day as plunging. We plunge into pure ethane (Leica EM-GP).
Best,
Sharon

-----Original Message-----
From: 3dem-bounces at ncmir.ucsd.edu [mailto:3dem-bounces at ncmir.ucsd.edu] On Behalf Of James Conway
Sent: Wednesday, May 02, 2012 5:31
To: 3dem at ncmir.ucsd.edu
Subject: Re: [3dem] Ethane - propane mix

I routinely use ethane/propane on a vitrobot and TF20 with Gatan 626 holders and I don't see vacuum problems on entry. I would expect the vacuum of the airlock and the turbopump (60 sec entry), plus the elevated temperature (-175 to -180C), to take care of any liquid remaining on the grid. As an earlier poster suggested, you can put filter paper between the metal cryogen cup and plastic of the vitrobot cup to get it cold and held firmly for blotting after plunging. I used to do this to avoid ethane ice interfering with the clip ring on the 626 cryoholder, but stopped when I switched to ethane/propane.

Contaminants in the ethane or propane tanks are another problem. You may want to clean the cryogen cups too in case residual oil coats the surface and floats off in the liquid. A plasma cleaner is supposed to be good to eliminate hydrocarbons amongst other impurities, although its an expensive choice.

Best,

James Conway

On May 1, 2012, at 4:02 PM, William Rice wrote:

> 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

----------------------------------------------------------------------
James Conway, PhD.,
Department of Structural Biology
University of Pittsburgh School of Medicine
Biomedical Science Tower 3, Room 2047
3501 5th Ave
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U.S.A.
Phone: +1-412-383-9847
Fax:   +1-412-648-8998
Email: jxc100 at pitt.edu
Web:   http://www.structbio.pitt.edu/main/people/faculty/71-conway  
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