Dear Yannick,
This is reminiscent of a problem I saw with a spectrometer during my PhD. In
our case there were times where at least one gradient pulse would not fire
as intended, mismatching the encode/decode of the spatial dimension, leading
to random points in the DOSY showing close to zero intensity. Our situation
was due to previous damage from a broken sample tube leaking corrosive liquid
into the probe and damaging the gradient coil. Your situation is probably not
exactly the same, but makes me think that there is something causing a mismatch
in your encode/decode pulses. Perhaps something causing intermittent short
circuiting (unlikely if the issue is persistent across different probes), or
maybe the recovery delay for the gradient ring down being too short. I imagine
it’s unlikely that it’s something in the pulse program code
that was changed, but perhaps a delay that was input expecting units of ms was
actually in units of us. If that is indeed the problem, the decrease in signal
would be correlated to which gradient strength was measured right before. A
quick test of this could be to just make an edc copy of a previously functioning
DOSY from a 1-2 months ago and run it to check for the anomalous behavior.
Best,
Adrian
On Dec 8, 2023, at 9:59 AM, yannick.coppel via groups.io wrote:
Dear colleagues,
We'd like to ask for your expertise on a problem we've been experiencing for
several weeks with our Bruker NEO 600 spectrometer.
We are used to performing DOSY experiments on a regular basis, but we are no
longer able to do so. When we vary the intensity of the gradient linearly,
we observe random intensity changes that are clearly not related to diffusion.
Signals can drop sharply and then rise again. We have verified that the problem
is not related to convection. In particular, we see the same effects with
anti-convection sequences. We were unable to identify any gradient values that
were more problematic than others. We carried out a number of tests (non-linear
ramping, changing the order of the different gradients, play with gradients shape,
use of different topspin version ...) but no convincing results. In a way that
seems totally random, the signal decreases sharply for certain slices of the DOSY.
On the other hand, when we use the 1D versions, the behavior looks normal and if
we run a succession of spectra, we don't see this random behavior.
Have any users already encountered this problem or have any idea where it might
be coming from?
Thank you for your help,
Yannick
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Received on Fri Dec 08 2023 - 09:49:39 MST