[3dem] Thinner ice after several microscope uses
Terje Dokland
dokland at uab.edu
Tue Nov 25 08:13:02 PST 2008
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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