> I need to do a variable temperature experiment where
> I know the temperature quite accurately. I have some
> charts from an old Bruker manual that give the chemical
> shifts of 100% methanol and 100% ethylene glycol versus
> temperature. Does anyone know how robust these calibrations
> are? In particular, is the calibration thrown off by a
> bit of moisture in the solvent, picked up from the air?
> I noticed that Wilmad sells sealed tubes of these
> solvents which they call chemical shift thermometers.
> Does this imply that one needs to take a lot of care
> when preparing these standards?
> Thanks
>
What degree of accuracy do you need 1.0, 0.1, 0.01, 0.001? VT units
(on a clear day) are accurate to about +/-0.1 degree C. There is also a
temperature difference due to thermocouple position in respect to the
sample
space. If you are worried about accuracy of methanol shift differences
due to solvent effects, I suggest that you use a small methanol filled
capillary as
an internal standard in your sample tube.
The capillary tube can be positioned coaxially in the NMR tube by using
anti vortex plugs
to center and support them
Another method is to partially a 5 mm tube with methanol, then insert
a 4 mm tube
holding the sample into it leaving a thin film of methanol between the
tubes.
Regards Scott
A. Scott Chesnick
Senior Scientist / Biomedical Engineer
National Institutes of Health
In Vivo Nuclear Magnetic Resonance Imaging Center
NHLBI/LCE Bld 10 Room B1D-125
Bethesda, Md 20892
301-496-6564