Ron
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Ronald F.Federspiel Department of Chemistry
Director, USF/NMR Center University of South Florida
email: federspi@chuma.cas.usf.edu phone: (813) 974-2344
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On Wed, 13 May 1998, A. S. Chesnick wrote:
> Don Leek wrote:
>
> > 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
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