Hi Rajan,
David Doty talks about this in his article in Concepts in Magnetic
Resonance Vol. 10, page 133, (1998). Tables 3 and for have this
information.
Regards,
Jeff
Hi Rajan,
Field distortions at the edges of the plug are the main design problems.
Solvents and solids are generally diamagnetic, on the order of 100PPM. So,
the static field is severely distorted at their interfaces, which is right
where you want the applied gradient to determine frequencies most precisely.
(For the same reason that bubbles in a sample wreck the shim).
So try using susceptibility-matched plugs with your solvent.
Chloroform and Teflon (or even Kel-F) are a good combination.
If you want to make your own, you can find susceptibilities of solvents in
the CRC table; I've seen susceptibilities of plastics listed; maybe someone
else has too, who can also remember where.
Regards - Gerry
Gerard C. Chingas, Research Instrumentation Manager
Chemistry, COAS, MS 1520
Boise State University, Boise ID 83725
PH: 208-426-4913, FAX: 208-426-1311
gerrychingas_at_boisestate.edu
-----Original Message-----
From: rajan paranji [mailto:paranji_at_chem.washington.edu]
Sent: Tuesday, June 16, 2009 11:24 AM
To: ammrl_at_ammrl.org
Subject: AMMRL:Gradient strength calibration..
Dear Friends
For calibrating the Z-gradient strength in my probes, I use a sample
that basically has a polymer plug matching the U shape of a standard 5
mm NMR tube, that has a cylindrical shell scooped out. I can push this
plug into a 5 mm tube filled with water. Carefully done, the cylindrical
shell is now full of water and the polymer is of such a type that
contains no protons in it. I pipette out any water above the plug so
that the only 1H nuclei are those trapped in this 'cylindrical annulus
shell'.
The height of this 'cylindrical annulus' is precisely machined to be
5 mm. By applying various gradient % values and recording the 'top hat'
like profile from the water, I calculate the Hz per (cm -A), which I
convert to the more useful Gauss/ cm-A .
Thank you for indulging me up to this point of the narrative. Now,
the questions :
* Do you all use a similar setup or anything else to calibrate the
gradients (standard solvent with known D at a given temperature,
etc.) ?
* If it is the former, how reliable is your calibration and more
importantly, how do you cross check this ?
* If it is the latter, can you please share with the community, how
you do it so that mere mortals like me can reverse engineer it at
my end ?
Thank you as always and hope all of you from the Northern hemisphere are
enjoying a wonderful summer unfolding ...
Best Regards
Rajan
--
*_______________________________
Rajan K Paranji, Ph.D.
*NMR Facility Manager
Department of Chemistry
Room 65, Bagley Hall
University of Washington
*Seattle, WA 98195*
*ph: 206 685 2581 pager:206 680 3779
fax: 206 685 8665
email: paranji_at_chem.washington.edu
___________________________________*
--
Jeffrey H. Walton
UC Davis NMR Facility, 4303 Tupper Hall
Biomedical Engineering Graduate Group
One Shields Ave.
University of California
Davis, CA 95616
(530) 752-7794 (office)
(530) 752-6480 (MS1-D lab)
(530) 754-0133 (CalEPR, Chem 76)
(530) 754-8238 (Chem 93 lab)
(530) 752-3516 (FAX)
mailto:jhwalton_at_ucdavis.edu
NMR Facility: http://www.nmr.ucdavis.edu
CalEPR: http://calepr.ucdavis.edu
Britt Lab: http://brittepr.ucdavis.edu
Biomedical Engineering:
http://www.bme.ucdavis.edu/profiles/gradgroupfaculty/walton.html
Received on Fri Jun 19 2009 - 09:11:04 MST