Department of Chemistry,
University of Alberta
NMR News 2005-02
News and tips from the NMR support group for users of the Varian NMR systems in the
There are no fixed publishing dates for this newsletter;
its appearance solely depends on whether there is a need to present information to the
users of the spectrometers or not.
Other content of this NMR News is no
longer meaningful and has been removed May 2010.
How can I make better NMR samples? This should be one of the most
frequently asked questions. Unfortunately, it isn't and most NMR users
do not care nearly enough about the quality of their samples and the
implications for the resulting spectra. Based on extensive experience, a
document was created by the people at the front of the NMR service: Glen
Bigam, Lai Kong and Mark Miskolzie. It is available in
PDF format - whatever your format
preference: please read it and follow
Automatic selection of plotter/printer
in remote processing sessions
More and more research groups use remote access from Macs and PCs in
their labs to process their NMR data. So far it was necessary to select
a plotter located in the research lab manually (a macro was created for each
group to make this reasonably easy). Even better, Mark Miskolzie created a neat new
macro which is used by the VNMRJ startup script; based on the remote
username it selects the appropriate plotter/printer automatically. In cases where there are two or
more printers in a research group, a decision was made to select one by
On the other hand, if
the user is logged in at the d601 or ibdw keyboard then the
directly attached 8.5 x 11 plotter is selected.
Time Limit on Data
created by gennmr
The replacement of an old hard drive with a much larger new one, has
made it possible to extend the "grace period" of data recorded in the
general gennmr account from 120 to 180 days. Users
of gennmr are reminded of this limitation every time they start
VNMRJ. This change has no effect on any other accounts, gennmr is
the only one with a time limit.
NMR Sample Preparation 
(for a PDF version of this document
To obtain high resolution NMR spectra it is necessary that your
NMR sample is free of suspended material (precipitates, dust, etc.).
Suspended material present in solution will increase the line width of the
spectrum; broad spectral lines reduce spectral resolution and no amount of
shimming can correct for this. Suspended material can
easily be removed from an NMR sample by constructing a filter using cotton wool
as a filtering agent . Conversely, glass wool is a
very poor filtering agent since glass wool does not filter out small particles,
whereas cotton wool tends to filter out the smallest of particles. A filter can
be made by placing a small amount of cotton wool inside a Pasteur pipette as
shown in Figure 1.
Pasteur pipette with cotton wool
Note that the Pasteur pipette has been cut to facilitate handling of the cotton
wool. Alternatively, the cotton wool can also be pushed down an uncut
long  pipette with the
help of a second pipette (this method was used in Figure 2 to position the
cotton). The solute of interest can then be dissolved
in a separate glass vial using less than the final volume of deuterated
solvent (e.g. CDCl3,
etc.) required to make your NMR sample. After the solute has been dissolved it
can be transferred directly to a NMR tube by passing the solution through the
cotton filter as shown in Figure 2.
Filtration through cotton wool
NMR request sheet depth
Finally, the sample volume can be adjusted by adding the remaining solvent to
the NMR tube so that a final sample volume of ~700 mL or a sample height of
~55 mm is reached (Figure 3), followed by
shaking of the sample to effectively mix its content .
The suggested sample
volume for our instruments is 700 mL.
Trying to concentrate your sample by reducing the sample volume is not
recommended. A short sample (i.e. volume less than 500 mL) can only be shimmed
through tremendous effort and this time can be much better spent acquiring your
Adapted from the Chem 241/341 sample preparation guide by Dr. Jason
Cooke, whose students consistently submit some of the best NMR samples seen by
the NMR Service Lab.
Medical cotton is reported to be free of compounds that can be extracted by
organic solvents (A.E. Derome, Modern NMR Techniques for Chemistry Research,
Pergamon Press, 1987).
9” pipettes are sufficient (no need to buy the much more expensive 10.5” type)
 Failure to mix the contents of the
sample tube results in a concentration gradient which degrades spectral quality.
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