Why is it required to use a Deuterated solvent?
The LOCK
In high resolution NMR, one often wants to resolve signals in the proton spectrum which are 0.1 Hz apart. This means that the magnetic field should be homogenous at any given instance. The magnetic field drifts (changes) with time. This slow drift is compensated for by the field-frequency lock, which is a feedback system designed to keep the field at a steady value.
The lock uses the 2H NMR signal from a deuterated solvent used to prepare the sample (most commonly CDCl3 or D2O in case of biological samples). The lock is a feedback system: if the field changes, the deuterium line shifts, resulting in an error signal, which in turn alters the field in such a way as to bring the line back to its position.
The field is distorted by the sample itself, due to the change in magnetic susceptibility at interface between medias: solution-glass-air. This means that the field needs to be corrected for each sample. There are a number of coils which overlap their field with the main field, which can be used to correct the homogeneity throughout the sample.
Address:
C. Eugene Bennett
Department of Chemistry
406 Clark Hall
Prospect Street
P.O. Box 6045
West Virginia University
Morgantown, WV 26506
Phone:
(304) 293-3435 X6439
Fax:
(304) 293-4904
Email:
Chemistry@mail.wvu.edu
