Dear AMMRLers,
I've seen some amazingly fast and helpful crowd-problem-solving on the
AMMRL network lately, and so I thought I would share my own issue hoping
for a similar response ;)
We have a relatively newly installed AVIII Nanobay 300MHz system (with
an older ultrashield magnet) used in open-access for routine 1D NMR. The
2D experiments are however plagued with horrible T1-noise streaks and we
identified some major field instabilities as the most probable source of
the problem. If we run a 1D 1H continuously without lock, we see erratic
field jumps of up to +/-30 Hz! Curious however is that this phenomenon
does not seem to occur completely randomly. For instance: it seems that
there are periods of 5-8 minutes every 25-35 minutes where they are more
intense. And nights between approx 11pm and 4am, the interferences are
almost completely gone. To illustrate what I mean, I've attached a
printout of the 2d stacks (each column represents 2048 1D 1H measured
every 2 seconds)...
This is not observed on 400, 2x 500 and 600MHz spectrometers sitting
only a few tens of meters away.
Of course, the night relative calmness and "regular" more intense
periods made us look into public transport schedules. The closest
streetcar stop is 400m away, but the schedule correlates quite wellwith
this phenomenon (for instance, the first one runs at 4:30, intervals are
20-30 minutes).
So my questions are: what could be causing these disturbances and how?
And of course, what can we do about it?
best regards
Chris
--
Dr. Christophe Farès
Head of the NMR Department/Leiter der NMR Abteilung
Max-Planck-Institut für Kohlenforschung
Kaiser-Wilhelm-Platz 1
45470 Mülheim an der Ruhr, Germany/Deutschland
Tel: +49-208-306-2130
E-mail: fares {at} kofo.mpg.de
Web: http://www.kofo.mpg.de/en/research/service-departements/nuclear-magnetic-resonance-spectroscopy
Received on Thu May 28 2015 - 22:17:53 MST