Hi Ken,
Great set of questions. I have always worried about VT because it would be
relatively easy to significantly damage the spectrometer (with one significant
probe damage and one big danger to the magnet happening during my first
few years managing a lab of chemists). Look forward to reading replies.
*
Do you require a specific grade of NMR tube?
I never set a rule about this, other than no chipped tubes (not supposed to
be used even when not doing VT).
*
New NMR tubes?
Didn't set this rule. Work done at pressures above 1 bar need thicker wall
tubes, and new tubes are correct.
*
What buffer do you allow between the solvent freezing/boiling point and the
target temperature? 10, 15, 20 degrees?
10 deg is reasonable when the researcher is checking the temp directly prior
to doing the VT expts using a VT standard or thermocouple. Careful
consideration/understanding of the gas flow is critical.
*
Anything else I'm missing?
Anything sealed should be tested outside the spectrometer first (including
when I do experiments for ppl). We had one sealed sample explode many years
ago, taking out the probe coils (expensive!).
No blue spinners for any VT work. I've found the white kel-f spinners to be
adequate for all other temps we've worked at.
The big danger to the magnet was me being not smart. A Varian probe was allowed
to run very cold (-100C) overnight during a humid June day. 1" of ice on the
top of the magnet next morning (and me apoplectic).... I had a cap and tube
made that fit the top of the magnet bore tube that ran the VT exhaust gas
away from the magnet after this.
Insist that researchers be trained in detail prior to approval for them to
do VT over larger ranges of temps.
Charlie
________________________________
> 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
> Subject: [AMMRL] Facility policies for Variable Temperature Experiments?
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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