[3dem] Re: 3dem Digest, Vol 44, Issue 3
DocDave50 at aol.com
DocDave50 at aol.com
Sun Apr 3 15:11:25 PDT 2011
I have not had the opportunity to exercise to use the Joel scope but the
following procedure works excellent on the Tecnai scopes. Of course, the
major issue is the holder type being used. It's a bit different using an
Oxford Holder than the Gatan Holder but the principle is still the same.
When using any of these holders, it is best if you can have some reserve
left in the dewar after insertion. One possible issue to be concerned with
when dumping all of the Liquid N2 is that it is possible to get some on the
viewing screen if not covered, a second is that it is the cause for the
cracks that appear on the scope desk top.
On the Tecnai series scopes, using Gatan holders, you rotate the
Goniometer to -55o, start the TMP to evacuate the airlock and remove most of the N2
in the dewar leaving residual liquid N2. Upon removal from the Transfer
Station, the holder is rotated 90o such that the mouth of the Holder would be
facing away from the front of the microscope and the dewar/alignment pin
at 90o and oriented with the airlock assembly. Since the TMP is up to speed
and the airlock pumped, you fully insert the holder with no loss of
remaining N2. Since the TMP is already at speed, it starts pumping the airlock
immediately limiting the potential for ice contamination on the cryo-shield.
Once the Airlock is fully pumped, rotate the Holder (without pulling or
pushing) to the 0o position (opening to the top), and then, while holding
the dewar stable, rock the Goniometer back to zero. At this point, the
Holder will pull into the microscope and the Holder Dewar is refilled with
Under these conditions, the dewar always has residual N2, there is no need
to dump all that N2 out...on whatever...the desktop (causing
cracks)...potentially the front screen (potentially imploding the Camera
Chamber)...styrofoam box (throwing away all that N2)...whatever. With the dewar topped
off and some time allotted for sample stabilization, away you go to collect
data. Under these conditions, I have found that the sample stabilizes to
drift rates less than 1A/sec reasonably quickly and I rarely have ice
contamination. I can't say that this is related to the maintenance of liquid N2
in the dewar but it works quite well.
My only concern regarding the approach you are outlining below, Jim, is
that it would appear that you are inserting the holder into the airlock and
then starting to pump the airlock. I'm not sure what the JOEL designation
for the airlock, which opened, pumps the inner airlock (it is N2 on the
Tecnai), but you will find it much easier to pre-pump the airlock prior to
insertion of the holder. It is, then only moments, before the airlock is fully
pumped such that holder insertion can commence rather than 5 minutes.
Another benefit to the -55 counter clockwise compustage rotation is that the
holder insertion is easier because it's easier to hold the dewar at that
angle and you have obvious points for aligning the holder as you are moving it
from the transfer station to the scope.
David W. Chester, Ph.D.
In a message dated 4/3/2011 3:00:06 P.M. Eastern Daylight Time,
3dem-request at ncmir.ucsd.edu writes:
Before cryoEM sample holder insertion, it is rotated 90 degree, so most
liquid N2 is poured toward user from dewar. I heard that new TEM goniometer
could be tilted before holder insertion. Anyone try it with older TEM?
I'm thinking two ways for our JEOL2010F.
1) tilt gonimeter +60 degree, insert sample holder (dewar is -30 degree),
flip airlock switch to "PUMP", after green light is on and wait for another
~5 min, turn the holder clockwise ~30 degree (now dewar is straight up),
tilt gonimeter back to +30 degree, then turn the holder clockwise another
~60 degree (now dewar is +30 degree right), and finally tilt gonimeter back
to 0 degree (now dewar is straight up).
2) tilt gonimeter +45 degree, insert sample (now dewar is -45 degreet),
airlock to "PUMP", after greenlight is on and wait for ~5 min, turn the
holder ~30 degree (now dewar is -15 degree left) and another ~60 degree
dewar is -45 degree), finally tilt gonimeter back to 0 degree.
The first method need tilt gonimeter two times at high angle, but the
holder's dewar is only rotated within 30 degree.
Anyone try it on JEOL2010F? If it works, it reduce one hazardous operation
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