[3dem] Ethane ice on Vitrobot frozen grids

[Bill Tivol]

On Dec 12, 2008, at 12:27 PM, Paul Keller wrote:

> I was wondering if anyone on the list had any insight into something  
> I observe regularly when using our Vitrobot (Mk II); the formation  
> of a layer of ethane ice on the grid during transfer from the liquid  
> ethane cup into the outer ring and grid storage box. The grid cannot  
> then be used until the ethane ice is removed.
>
> The ethane layer almost always seems to dissipate if I leave the  
> grid in LN2 storage at least overnight, but this is not always  
> desirable.  Does anyone on the list have any advice for removing the  
> ethane ice without damaging the underlying sample, or preferably,  
> techniques for avoiding the formation of an ethane ice layer entirely?


Dear Paul,
	I have always looked upon the ethane layer as a protection against  
ice crystals from the atmosphere above the cryogen falling onto the  
grid during transfer.  The ethane will evaporate quickly in the  
airlock of the scope during pumpdown, so I haven't considered it to be  
a problem.  However, if it is a problem for your applications, you  
might consider using a mixture of propane and ethane as a cryogen.   
The paper by Tivol, et al. in Microscopy and Microanalysis, Vol. 14  
Num. 5 pp 375-79, October, 2008, describes the cryogen and shows some  
results.  Since the mixture remains liquid at 77 K, it will readily  
disappear from the grid, so you can examine the grid immediately after  
freezing.
Yours,
Bill Tivol, PhD
EM Scientist
Ultrafast EM Facility
Noyes Laboratory, MC 127-72
California Institute of Technology
Pasadena CA 91125
(626) 395-8833
tivol at caltech.edu

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