[3dem] Thinner ice after several microscope uses

[Terje Dokland]

The purpose of the cryocycle is to prevent contamination of the ion  
getter pumps as the cold trap warms up. It shouldn't affect the  
performance in the short term, I think.

I think it is VERY important to cool the coldtrap fully before  
COOLING the holder, but inserting a warm holder shouldn't have any  
effect. But it shouldn't take more than about 45 mins.

I have never observed the effect you describe on our Tecnai F20, but  
we had a JEOL 2010F microscope that could never be used for cryo  
because the contamination was so bad (not just for the first sample),  
so it could definitely be microscope-specific.

Terje

On Nov 25, 2008, at 10:00 AM, Eduardo Sanz García wrote:

> Henning Stahlberg wrote:
>> Hi,
>> We had a similar phenomenon: Ice contamination on cryo-EM grids  
>> was sometimes but not always quite bad, but the second inserted  
>> grid was often less contaminated than the first one. This was on a  
>> JEOL JEM-2100F.
>> I believe the problem might have been related to some weird air- 
>> pocked formation in the goniometer, potentially between two  
>> consecutive O-ring sealings. When we left the goniometer without  
>> sample holder over night, air might have slowly accumulated  
>> somewhere and was inserted into the column during the first sample  
>> transfer. We tried leaving a holder in the goniometer over night,  
>> but that did not significantly improve the situation, as if the  
>> "leak" only occurred during sample insertion.
>
> I was thinking in the same lines than you, a problem with the  
> goniometer-airlock, but yesterday, I had another idea of what could  
> be wrong.
>
> If for some reasons the cool trap takes a lot of time to cool off,  
> like  1 or 2 hours, the cryoholder could function like a cool trap  
> building contamination in my grid. On the other hand, if the  
> microscope have been working all day long, then all the contaminant  
> have been trapped during the day, then I will not have problems of  
> contamination.
>
> Two questions for everybody:
>
> * How long do you let the cool trap to cool off before inserting  
> the cryoholder?
> * Is it necessary to do a cryocycle every night?
>
> Thank you very much.
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