Hello Luke,
Sealing your own tubes is easy to do and I have never had any problems with
home-sealed tubes in the NMR (and I have no experience with glass blowing
apart from making capillaries and sealing NMR tubes). It just takes a bit
of practice to get the knack of doing it right and since I do it very
irregularly, I keep a stash of broken NMR tubes to practice on before I seal the
real tube. People make an issue of using an open flame with combustible solvents
(ummm, what do you think the gas is ?) but it is not a problem with such a
length between the tip of a 7" tube and top of the solvent. A very hot flame
is not required and I just use a pen style torch running on butane that you
can buy from a hardware store or a store like Walmart. The biggest danger I
think is if you use liquid nitrogen to "safely" keep the solvent away from
the open flame by immersing the lower section of the tube in liquid nitrogen
(seriously, how much solvent is going to be ignited ? I have never had an
issue or an indication of any solvent combusting on an observable level),
but this runs the risk of creating a bomb. I cannot remember the eminent
scientist who lost eye after sealing an NMR tube using liquid nitrogen after
he took too long and condensed too much liquid oxygen in the NMR tube. Of
course a vacuum line with capability of attaching an NMR tube solves this
issue but I have found it unnecessary. In all the years I have never had
a sealed NMR tube break or leak once I tested for a leak after I had finished
sealing the tube. One tip is to try to not draw out the molten glass like
you would if you wanted to make a capillary, it is possible to get a fairly
decent short and blunt sealed end by twisting and pulling just a little bit,
it only requires some practice.
As for making your own thermometers, I do not recommend it, especially for
the methanol one as the performance (i.e. the temperature you calculate from
the signal difference) varies greatly with how much acid is present, and
water too I would imagine. To be sure that your thermometer works and you
have a correct calibration plot/equation it is best to calibrate it against
a known thermometer or use a thermocouple that can be inserted into the magnet,
in which case why not just use a thermocouple ? This is my recommendation and
is what I use when I need to know the real temperature. We tested a bunch of
methanol standards (some very old) several years ago that we had on hand,
and also some we made ourselves (total disaster !!) and we were surprised
at the variation and how erroneous they could be. As a final note, using a
thermocouple means you can immerse it in the same solvent as what you use
for your sample, so the thermal effects of decoupling might become more
apparent.
Good luck,
K. Klika
________________________________________
> From: Fulton, Luke via groups.io
> Sent: 17 September 2025 21:10:36
> To: main_at_ammrl.groups.io
> Subject: [AMMRL] DIY NMR thermometers? #Question
Hi all,
Over the last two days I checked every nook and cranny for my thermometer
standards, and thankfully just found them. With budgets tightening I had
started entertaining the idea of making my own replacements, and perhaps might
have to someday. I have some amateur glass blowing experience and am confident
in avoiding stressed-glass tube failures inside a magnet, also personal injury.
My thought was to use methanol and ethylene glycol 100%. But I'm not sure how
strict they ought be for solvent purity requirements. As in, a several year
old 4L bottle is fine, freshly distilled only, anhydrous analytical HPLC
grade or bust...
Would anyone comment on how robust the temperature response curves for ppm
deltas actually are? Or if you've found flame sealing your own standards in=
house worthwhile and not just a fool's errand?
Kind regards,
Luke
Luke Fulton, PhD
CHEM BLDG R003
NMR Core Facility Director
Unit 3060
COR2E & Department of Chemistry
55 N Eagleville Road
University of Connecticut
Storrs, CT 06279
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Received on Wed Sep 17 2025 - 12:16:22 MST