I wish to thank Kirk Marat, Phil Dennison, and Jim Frye for their advice on
137Ba NMR. I will try again with a 0.5M BaCl2 solution. The following are
their messages:
---------------
The one reference that I checked listed 137Ba in BaCl2 as having
a linewidth of about 2000 Hz and T1s of less than 0.0001 s. This means that
you are probably loosing most of your signal in that 150 us delay. You
could also
use a much shorter relaxation delay.
My reference (Brevard and Granger) used 0.02 s repetition rate (50 scans per
sec)
a 0.5 M solution, 90 degree pulse, and 55,000 scans with a 10 mm sample on
a 250 MHz spectrometer.
---------------
I have a photocopy of part of a long out of print book on
multinuclear NMR. The second section, called 'Isotope NMR
Fingerprints' lists nuclei, reference samples, shift ranges etc. The
book is old, and experiments were performed on a 100MHz instrument.
For 137Ba, they use a 0.5M solution of BaCl2 in D20, and get a very
broad peak after 55,000 scans. The peak width is 2000Hz. They use a
0.02s repetition rate, so relaxation is quick.
---------------
Your saturated solution is very conductive and will lengthen the pw90 and
decrease sensitivity because probe Q is lower. However, you should still
see a signal. Use much faster repetition, maybe 0.01 s. Don't suppress
ringing with a long dead time. After you see a signal and calibrate your
pw90, suppress ringing with the RIDE (or the equivalent aring) program.
For a solid standard, try lithium barium titanate.
-----------------
Hsin
----- Original Message -----
> From: "Hsin Wang" <wang_at_mail.csi.cuny.edu>
> To: <ammrl_at_ammrl.org>
> Sent: Wednesday, November 03, 2004 2:38 PM
> Subject: 137Ba NMR
> I am trying to calibrate 137Ba pulses on solid state probes with a
> saturating BaCl2/H2O solution. I was expecting to see the signal in a few
> scans because 137Ba has similar absolute receptivity to 13C. But I have
> searched in a range of +/- 50KHz with hundreds of scans and have not found
> the signal (I have tried on a wideline probe, by Varian, and a CP/MAS probe,
> by Doty, both run statically and tuned well, on a 300MHz Unity Plus). I
> assume that I can use short relaxation delay and have used d1 between 0.5
> sec and 2 sec. To avoid acoustic ring down, I used a delay of 150us before
> acquisition (rof2, in vnmr). I would appreciate any advice how to calibrate
> the 90 degree pulse.
>
> Hsin
>
> --
> Hsin Wang, Ph.D.
> NMR Facility Manager
> College of Staten Island
> 2800 Victory Boulevard
> Staten Island, NY 10314
> Phone: 718-982-3809
> Fax: 718-982-3910
> Email: wang_at_mail.csi.cuny.edu
>
Received on Mon Nov 08 2004 - 08:55:30 MST