Dear Colleagues,
I would like to ask your help in the following (for open access
facilities certainly standard) issue, since I did not find much
guidelines while searching the AMMRL web site. I will post a summary
afterwards.
As general information we are an open access laboratory with about 130
users, four liquid state, one solid state, and one instrument in the
teaching laboratories. The probe in point gets taken out and is put back
into the magnet once a week to accommodate observation of other nuclei.
The problem was the following: The inner coil on our Nalorac 400 MHz
quad probe (H/F/C/P) broke. This coil is glued onto a glass insert in
which the samples rotate. So I think both mechanical stress and thermal
stress could cause the problem. The incident happened during or after
cooling down of a VT experiment up to 90 degree C. I would like to ask
you for guidelines for users and tricks and tips for us on how to extend
the life of the coils. This one lasted only 2.5 years (is that normal?).
_________________________________________________________________________________________
Points that I come up with follow. Please comment on them and add
others:
For the users:
- Avoid mechanical stress:
Use high quality cylindrical tubes and treat them well (Heating in the
oven? The professors say "we have always done it that way!"). Some tubes
(especially J-Young tubes) are visibly fixed up (man, am I trying to
fight that one!!).
- Oxidation and damage during VT-work:
What are your rules about air/nitrogen usage, duration of VT work,
user's presence during VT work, spinning during VT experiments. Also,
lately I caught a user trying to run a reaction 10 degrees above the
boiling point in a "sealed" (i.e. J-Young) tube. He asked for help
because he had trouble keeping the lock stable. The professors comment:
"I have always done that." Could the formation of bubbles cause
imbalance? I think this is an unsafe experiment, do you agree?
- any other tips:
_________________________________________________________________________________________
For the staff:
- We are trying to clean the turbines, upper stack and inner glass tube
of the probe regularly. The students are trained to clean their sample
tubes each time. Anything else that we could do better?
- How do you align the probe and upper stack? We find the recommendation
to insert a sample and watch for scratching may be by using a marker
very dissatisfying. We tried to design a long tool that lets us level
the upper stack, but there is still too much play. The distances between
where it matters, i.e. at the bottom of the upper stack relative to the
top of the probe, versus where things get set, i.e. at the top and
bottom of the magnet, for top stack and probe, respectively, is just too
large.
- any other tips:
__________________________________________________________________________________________
Thank you for your help.
Happy and save resonating
Ulli
--
Ulrike Werner-Zwanziger
Department of Chemistry
Indiana University
800 E. Kirkwood Ave
Bloomington, IN 47405-7102
Phone: (812) 856-4629
Fax: (812) 855-8300
WWW: http://nmr.chem.indiana.edu/~ulli
Received on Fri Apr 28 2000 - 12:19:23 MST