We can do 2H
NMR in one of two ways: (1) tune the observe coil of a broadband probe
to the deuterium frequency. This is basically the same as doing
any X nucleus, except we will disconnect/disable the lock while
observing deuterium. The best place to to this experiment is on Daytona
using the broadband AutoX probe. (2) Use the probe's lock channel for
direct observation. The first method has the highest sensitivity
for observing deuterium. The second method is fast and easy, because no
probe tuning is required, and will work as long as the amount of
deuterium is not extremely small. It can be done on any of the
spectrometers in the lab, since they all have a lock channel.
Keep in mind the following:
You cannot use the “Find z0” button while observing deuterium and you must turn the autolock feature off (alock=’n’). If the instrument searches for a lock when there is none, z0 is likely to be set wildly wrong and the peaks will be displaced in the spectrum.
Instructions for setting up the experiment:
1. Load carbon parameters
as a starting point.
2. Set up 1H gradient shimming (currently implemented on Hg2 and Daytona) by starting with Tools (on the top menu bar) -> Standard Calibration Experiments -> Set Up Gradient Shimming. Click the Defaults tab on the left. Set Relaxation Delay(s) to 3 and the Number of Scans to 1. Then click the Gradient Shim tab on the left. Click on the button that says PFG H1. Click on the Load map drop down bar and choose ‘toluene.’ Type pw=3 tpwr=50 gain=8
on the command line. Then click on Gradient Autoshim on Z. Typically it will do 3-4 cycles of shimming and then stop. After it stops, click Quit Gradient Autoshim.
(If you do not use 2H gradient shimming at other times, you can set this configuration up one time and leave it. If you use 2H gradient shimming on other samples with deuterated solvents, then you will need to switch to 2H gradient shimming by clicking on PFG H2 and selecting an appropriate map name.)
3. Go to the Acquire
-> Channels tab. In the Observe column, change the Nucleus entry
from C13 to lk (lk="lock"). Important:
change the 90 Degree at Pwr entries to 100 us at 45. (The lock
only handles low power, so the power must be reduced, and the pulse
width increased to compensate.) In the Decouple column, change Dec
On/Off entry from yyy to nnn. (Although you can do 1H
decoupling, in practice, it will not appreciably narrow your lines.) On
the Acquire -> Acquisition tab, increase the Acquisition time entry
to 2 seconds.
Type alock=’n’ and then su.
5. Turn the spinning back on by going to the Spin/Temp tab, entering 20 in the spin rate box, and clicking on Regulate Speed.
6. After spinning is
regulated, type ga to acquire the spectrum. The sensitivity for enriched 2H
is similar to 31P, i.e. worse than proton, but much better
than natural abundance carbon. The displayed chemical shifts will be wrong; use the
solvent peak to reference them correctly.
7. In order to restore
normal lock operation, load the standard parameters for any experiment,
then type su.
8. If the 2H sensitivity is insufficient using this method, it is probably better to observe 2H on Daytona using the broadband channel. For that, change the nucleus from C13 to H2; leave pulse length and power the same. Then remove the 2H band stop filter from the broadband observe path, and tune and match the broadband coil to 2H. Don't forget to replace the 2H band stop filter at the end of the experiment!