Dear AMMRL - We have an Bruker AV-500 here that works predominantly under an
automation environment using a B-ACS 60 with ICON-NMR. I am sure what I am
about to say will come as no surprise but a major source of inefficient use
of the spectrometer concerns the observation of the 13C nucleus and setting
the number of transients. The way I have configured the Bruker "day-night"
priority setup is based on the following experiment durations:
- Duration 1 is 20 minutes; any day experiment that is less than 20 minutes
can run between the hours of 9 - 5, Monday to Friday. If the experiment
will be longer than 20 minutes, the user must select the night version of
it.
- Duration 2 is 1 hour; the implication here being if a night experiment is
less than an hour in duration and the spectrometer is sitting idle during
the day, this night experiment can run. This means that any experiment an
hour or longer has no chance of running during the day.
As a result of this configuration, two of the most popular durations we see
are 19 min 59 sec and 59 min 59 sec. Particularly with 13C observe, the
"19:59" bunch want their data as quickly as possible and so hope for the
best in terms of their 13C spectrum. More often than I'd care to admit,
they generate a beautiful spectrum of their deuterated solvent. The "59:59"
bunch are usually in no particular rush for their data and want the best
spectrum they can get within this timeframe. Quite frequently, the S/N from
these experiments exceeds a gazillion and the information required could
have been obtained in 5 minutes.
I've had it in the back of my mind for some time now the idea to create a
composite experiment where the number of scans for the 13C observe
experiment is defined by the S/N obtained from the proton observe
experiment. In other words, based on the number of scans used in the 1H
detected spectrum and the resulting S/N, have a scaling factor defined in an
automation program to intelligently set the number of transients for the 13C
detected experiment. A second approach might be to forget about the proton
experiment and instead split the 13C experiment up into blocks of something
like 128 scans and after each block completes, process and check the carbon
S/N. Once it reaches a predefined threshold, stop. Clearly, either
approach would require some upper limit in terms of time.
Surely, the problem with ns/nt that I describe here is not unique and anyone
operating an automation setup can relate. Thus, before moving forward with
this project, I thought it would be useful to throw it out to the group and
see if any of you have tried something similar. If so, did it work and if
so again, what approach worked? If you tried but decided it was not viable,
what were the problems?
Thanks in advance for any feedback and I will of course post a summary if
interest warrants.
Cheers,
Mike
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Michael D. Lumsden, Ph.D.
NMR Facility Coordinator
Room 428, Atlantic Region Magnetic Resonance Centre
Department of Chemistry, Dalhousie University
6274 Coburg Road
Halifax, Nova Scotia, Canada
B3H 4J3
phone: 902-494-1635
FAX: 902-494-1310
http://armrc.chemistry.dal.ca
Received on Wed Aug 20 2008 - 05:22:44 MST