Dear All,
We have a venerable but very fine Bruker 400 (uograded in 2000) and a
2 year old Bruker 600. Before I allow users to book an overnight run
on the 400 where we have an open-shop, I insist on seeing the user's
1H spectrum for the intended compound. I judge the proton for purity
and sample strength. Impure samples are usually rejected for overnight
2D'sand weaker samples are redirected to the 600. I use the relative
size of the solvent signal to the sample signals, the base line noise
and the SNR to judge strength.
We only allow a few students to tune and match the probe since we have
suffered damage when occasional tuners have adjusted the probes.
Users are supposed to call a tuner if the probe adjustment is 'out':
They rarely do and many decent samples have been sent to ther 600
needlessly because the 1H tuning was way out. I have created a device
for tuning 1H remotely from the operator console.
It is purely mechanical and incorporates a
'slipping clutch' or 'torque limiter' to prevent the user applying too
much force to the tuning screw when it is at one end of its travel
(which it should never be). The system works well and in 2 weeks of
operation there have been no hassles. The device can be removed for
probe changing in 2 (TWO) seconds and refitted in 10 seconds (you need
to re-engage the 'screw-driver').
Generally if the 1H tuning is correct the match is not far out. We
now get good protons (and Cosy/Noesy) and avoid the problems which
arise with DEPT when the 1H is mistuned. Underlying this is that we
get accurate 1H 180 degree pulses. Of course the Indirect 2D's have
to be better too and even carbons/X-nuclei get better decoupling.
I am working on something similar for adjusting the X-nucleus tuning
slider. If you would like photos of the 'device' please contact me.
The total cost of parts was less than US$20 and I made it myself - no
need for work-shop time and money.
It is a real pleasure to sit at the desk and tune. Its easier and
quicker than shimming and I don't have to leave my chair!
Sincerely,
Andy
Received on Tue Apr 22 2008 - 23:12:44 MST