Standards
RDUDLEY (rdudley@ARSERRC.Gov)
Tue, 01 Apr 1997 09:01:33 -0500 (EST)
Hi All,
Last week I was in sunny Florida and last night we had a blizzard in
the Philadelphia area. Add to that power outages and trying to bring up
spectrometers.
One of the topics discussed at the AMMRL meeting was test standards,
spec standards. Solid state NMR spectroscopy presents a special problem as the
s/n is dependent on how will one packs the sample. Generally one obtains a
CPMAS spectrum of adamantane and hexamethyl benzene. In addition we had a C13
CPMAS NMR spectrum of glycine. I have yet to figure that one out. One is
generally left on ones own for stting up other nuclei. We do a lot of N15
CPMAS NMR spectroscopy in our lab and I thought I would let you know how we set
up to observe that nuclei.
I know a number of people use 15NH4Cl as their set up sample. We have
not had a lot of luck with this compound. We find several 'matches' that seem
to be spinning speed dependent. Instead we use N15 labeled glycine. The
contact time is 5 msec and we use a recycle time of 1sec. The only difference
from C13 is we use a slightly longer 1H 90 deg pulse of 6 usec. The 15N peak
is fairly sharp and we collect 1k data points. We are able to match and tune
the probe at any spinning speed. Another advantage is one can use the glycine
N15 peak as a reference as its chemical shift is 31.5 ppm from anhydrous
ammonia. The proton t1 is approximately 1 sec so one should use a longer
recycle time for quantitative data.
I would be happy to FAX anyone a copy of our setup spectrum run on a
Bruker MSL-300.
Bob Dudley