Re: nmr sample volume

Charles G. Fry (fry@bert.chem.wisc.edu)
Thu, 05 Nov 1998 17:52:57 -0600

We have too wide a research base to mandate anything along
these lines. So I give a series of recommendations that the
students pickup on reasonably well. We recommend 507's for
1H work at 300 MHz; I really think 528's are overkill here.
528's are recommended for our 500's for 1H work; 535's only
if doing water suppression at 500MHz. For quick and dirties,
and X-nucleus work at 300, I've found the Thrift tubes to
work just fine (at < 1/3 the price). 507's at 500MHz
sometimes cause problems even for X-work, so I try to get
students to stick with 528's there.

Solvent volume is much more of an issue for me, particularly
with Varian probes. 80% of the trouble I see with student
shimming is too small a solvent volume; 90% of what's left is
improperly filtered samples or scratched tubes.

For Varian 5mm probes, going below ~0.5ml is deadly. Bruker
probes, at least the older ones we have that are 12mm in
length, are much more forgiving in solvent volume. I recommend
0.6ml Varian, 0.5ml Bruker. For a series of samples, getting
the user to get the solvent volume identical (use a pipet)
can make shimming through the samples after the first trivial.
Most important, though, is to get them to not try living on the
edge with solvent volume. That extra half-mil they are trying
to save (expensive solvent), or that extra 20% in conc is NOT
worth the potential trouble!! Hard to get them to
believe this...

We have had very good success with susceptibility inserts,
especially for 13C observe experiments when the amount of sample
is limited. You really do get 9x improvement in time for same
S/N, so I've pushed susc inserts real hard here. The inserts
must match the coil length (or a little longer), so users need
to know this for the system they are using.

For our sample changer at 300 MHz, we remove all submitted
samples that have less than 4 cm solvent (~5ml); it takes the
autoshimming routine too long if the solvent volume is less
than this.

At 11:02 AM 11/5/98 -0400, you wrote:
>Dear AMMRL members:
>
>I have been thinking to standarize sample volume/height and tube quality
>for routine and not-so-experienced nmr users in our department. I am sure
>these and similar nmr management issues were discussed before, but I want
>to receive some feedback from your own experiences.
> It is difficult to judge the quality of each nmr tube by routine
>student users, and I recommend using at least Wilmad 528-pp at 400 MHz or
>even at 300 MHz. The sample height for high resolution nmr in a 5 mm tube
>should be about 5 cm high. I have seen recommendation of 4 cm sample
>height, too. For expensive solvents, smaller sample height is, however,
>desirable.
>
>Thanks in advance for your comments,
>
>Sandip
>
>
>
>
>________________________________________________________________________________
>Sandip K. Sur, Ph.D. Email: sur@chem.chem.rochester.edu
>NMR Facility Tel.: (716) 275 4705 (W)
>Department of Chemistry (716) 275 0912 (W)
>B53B Hutchison Hall, R.C. (716) 586 7794 (H)
>University of Rochester Pager: (716) 275-4231 (ask for me)
>Rochester, NY 14627-0216 Fax: (716) 473 6889
>
>Thursday, November 5, 1998
>
>________________________________________________________________________________
>
>
>
>
>

----------------------------------------------------------
Charlie Fry Tel: (608)262-3182
Director, MR Facility Fax: (608)262-0381
Chem. Dept., Univ. Wisconsin
Madison, WI 53706 USA email: fry@chem.wisc.edu
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