AMMRL: temperature calibration by neat methanol and deuterated methanol

From: Robert Peterson <peterson_at_mbi.ucla.edu>
Date: Thu, 01 Jun 2017 14:28:43 -0700

Dear group,

Some of my users had reason to suspect that the temperature calibration
on one of our older instruments (with cryoprobe) was wrong. I've always
calibrated the temperature using pure methanol, but one of our users
said she had read that deuterated methanol is supposed to be better for
cryoprobes. The Bruker /calctemp/ au program references this paper for
using deuterated methanol to determine temperatures:

      Magn. Reson. Chem. 2007; 45: 175-178

And they do indeed claim that deuterated methanol gives better results
on cryoprobes than neat or concentrated solutions of methanol.

I decided to calibrate the temperature using both neat methanol and
methanol-d4. I took measurements with both samples at set temperatures
from 284K to 323K, at 3 degree intervals.

I analyzed the methanol-d4 data with the formula from the above paper (T
= 419.1381 - 16.7467*delta^2 - 52.513*delta).

I analyzed the neat methanol data four different ways. I used three
separate quadratic formulas, one of which is from the Bruker VT manual.
And I also used the linear approximation from the Bruker VT manual for
temperatures between 265-313K. These four methods for neat methanol gave
nearly identical results.

See the attached figures. They show the results from methanol-d4, and
neat methanol calibrated using the linear approximation from the Bruker
VT manual. The temperatures 314K and lower are different by 6 - 7
degrees between the two methods! Is this possible? Has anyone else tried
this? I haven't had the chance to try this on my other instruments*, so
I don't know what the result will be. But now I'm wondering if most of
our temperatures have been drastically off ever since we started using
cryoprobes.

*We have a new (two year old) Avance III HD console on one of our
instruments. The installation engineer did a temperature calibration on
that one using deuterated methanol. So apparently, Bruker does use
deuterated methanol to calibrated temperatures on cryoprobes.

Thanks and I will post a summary of the responses.

-Robert

-- 
-----------------------------------------------
Robert Peterson, Ph.D.
Facility Manager - NMR Technology Center
UCLA-DOE Institute for Genomics and Proteomics
UCLA Dept. of Chemistry and Biochemistry
phone: (310)825-1816
fax:   (310)825-0982
peterson_at_mbi.ucla.edu
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Received on Thu Jun 01 2017 - 11:35:20 MST