Hi Ken,
Rules I follow:
-strictly unbroken tubes with no chips or cracks (universal rule but I emphasize
for VT, sadly can't feasibly police it 100% for RT)
-for flame sealed tubes I would insist on inspecting their craftsmanship first
(hasn't happened yet)
-Our T ranges have been rather gentle, 0C-80C, so I haven't prohibited high
throughput tubes (perhaps I should?)
-I allow up to within 10C of a phase transition. To that end, it's important
to calibrate your thermocouple and make sure students are aware of however
its response curve behaves. Further you stray from RT the greater the the
rmocouple can deviate from true. Otherwise users can follow guidelines
exactly and still unknowingly overshoot their target, or worse, a phase
transition.
-Heating is done slowly using no larger than 10C increments, and thermocouple
must reach target before increasing again. I was trained that heating too
quickly can damage/burnout the circuitry. Perhaps engineering has solved
this concern in newer probes but I'd rather err on the side of caution.
-Users are responsible for readying probe for next person. That almost always
means returning to RT. Depending on your equipment that could foreseeably
take an hour or more. Users should plan accordingly.
Tricky question is whether users should be allowed to leave long VT runs
unattended. After everything is setup I'd prefer they check in on it at least
every 30 minutes. My biggest worry is someone walking out the lab, completely
forgetting about it, and then neglecting the equipment for hours or overnight.
Other Thoughts:
-Thermal cycling too quickly can wear out and crack the quartz inserts in the
probe. YMMV. Good idea to have spares on hand for replacement, especially if
VT becomes a staple experiment in the lab.
-If the experiment conditions were long/harsh I would want a RT measurement
before/afterwards to confirm probe condition. This can be quite irritating
for the user so exercise best judgment on when you think it appropriate.
-Whenever training the technique I highly recommend sticking to standards or
chemically inert samples. Kinetic studies are a common first request for VT.
It's near impossible to correctly design that experiment without experiencing
the practicalities firsthand. Those users that insist on trying it anyways end
up wasting hard-earned materials and regretting their decision.
-reminder that DMSO is a potential explosion hazard under prolonged heating
at high temperatures.
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
email: fko24003_at_uconn.edu
(alias): luke.fulton_at_uconn.edu
mobile: (603) 953-5275
Office: (860) 486-4069
________________________________
> From: main_at_ammrl.groups.io on behalf of Kenneth Sharp-Knott via groups.io
> Sent: Monday, October 20, 2025 10:46 AM
> To: main_at_ammrl.groups.io <main_at_ammrl.groups.io>
> Subject: [AMMRL] Facility policies for Variable Temperature Experiments?
*External sender: This message was not sent through the UConn email system.=
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ts, or requests.*
We're revamping and/or putting in place various policies/procedural documents \
now that we have moved on from the Era of the Flood and into the Era of
Shiny New NMRs.
I'm curious what kind of specific guidelines you have in place for variable
temperature NMR?
*
Do you require a specific grade of NMR tube?
*
New NMR tubes?
*
What buffer do you allow between the solvent freezing/boiling point and the
target temperature? 10, 15, 20 degrees?
*
Anything else I'm missing?
Thanks in advance!
Ken Sharp-Knott
Manager of Analytical Services and the NMR Facility
Department of Chemistry
Virginia Tech
(540)267-6502 (Cell)
(540)231-0885 (Office)
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