Many thanks to all who replied concerning problems with the
BSMS Autolock function on toluene-d8 (or any other solvent
with more than one signal, or mixed solvents). There were a number
of useful hints and suggestions.
Probably the most practical solution, provided by Clemens of BII, was to
use the XwinNMR "lock -noauto" command, which seems to be equivalent
to manual locking with the BSMS keypad lock button. It is necessary to do
a "lopoi" command first to set all of the lock parameters, and a macro can
conveniently combine "lopoi" and "lock -noauto" into one command.
The BSMS field value (edlock) must be up to date, and the correct lock shift
entered into the edlock table. Our biggest problem was in IconNMR, but it
turns out (well, I did finally look at the manual :-) ) that you can
configure
IconNMR to use the "lock -noauto" option on a solvent by solvent basis.
I did increase the edlock lock power setting for toluene a bit (but still
well
short of saturation) to help make sure it would lock even on a crummy
sample.
So far, this method seems to be working well, at least for our 300 which has
a
VERY low drift rate and hasn't required a change in the field value in
months.
A higher field machine may require more frequent updates.
The only possible drawback that I can forsee is that manual locking (keypad
or
XwinNMR) doesn't seem to do any lock gain adjustment, while AutoLock
does. I haven't had any problem with this so-far, but I will keep the group
posted
if I do.
Phil and Duncan suggested that if the field value were offset slightly (to
high
field ?) then the AutoLock function would pick up the correct peak.
I haven't had a chance to try this, however.
----------------------------------------------------------------------------
------------------
Clemens Anklin:
first you have to make sure that the field value in edlock is always up
to date.
Then you can force it to lock on to the nearest signal by typing "lock
-noauto"
In this case the auto lock will not be used but just the lock is
activated and will
lock on to the signal, if field is close enough.
----------------------------------------------------------------------------
------------------
Duncan Smith:
I have run many samples in mixed solvents which is a good model of the same
problem, i.e. more than one lock signal in the sample. I have found that
ensuring that you have the correct field value makes a big difference. If
you
lock manually, then set "BSMS field" from within edlock, and then change it
by
10 units it should work fine. I can't remember which way you have to change
it, just try both. When the autolock starts searching for a signal it
always
starts going in the same direction - just ensure the required signal is on
the
correct side of the default value.
----------------------------------------------------------------------------
-------------------
Jane Strouse:
The obvious solution mentioned for autolock on toluene unfortunately
does not work. If you set the aromatics in the edlock file, it will lock
on the methyl. Higher field does not help. We run into this all the time
at 500 MHz.
At this point the only solution is to use a manual lock. Just read in
the parameters from the edlock file using the lopoi command, then press the
LOCK (not AUTOLOCK) button. This problem is one that I have had
discussions with Bruker about. I am told that there are plans to deal with
it, but to the best of my knowledge nothing has yet been implemented. This
is a continual problem for us because I have a lot of users using toluene,
THF, and various mixtures of deuterated solvents. I would hope that a
solution is made available relatively soon.
----------------------------------------------------------------------------
-------------------
Phil Dennison:
This problem can also occur with other solvents with more than one peak,
such as methanol and pyridine. The solution is to update your BSMS field
setting, and to ensure that you have the correct signal on screen at the
time. For safety I tend to set up the lock on the correct peak, unlock, then
shift the field so that both lock peaks are to the left of the current
position.
Store this value as the BSMS field and all should be well. Until the filed
drifts enough for the process to be repeated, anyway!
----------------------------------------------------------------------------
-------------------
Cheers
-Kirk
Kirk Marat, Ph.D., NMR Facility Manager
Dept. of Chemistry and Prairie Regional NMR Centre
University of Manitoba
Winnipeg, Manitoba, R3T 2N2, CANADA
kirk_marat@umanitoba.ca
ph. (204) 474-6259, FAX (204) 474-7608
This archive was generated by hypermail 2b29 : Sun Dec 31 2000 - 01:15:03 PST