in the couple of the last weeks I bother with one sample showing
significant T1 noise within HMBC, ROESY, DQF-COSY ...
I think I excluded all common sources of T1 noise (spectrometer
work well with other samples, sample became filtered carefully,
shim is o.K., Lock is optimized ...).
Now I have a weak assumption what the reason could be and I am
looking if anyone else had comparable problems.
So, please let me describe my assumption.
The sample became measured at 300K. At this temperature
the sample shows two separate conformational isomers.
A few lines became broadened due to beginning exchange
phenomena. The temperature isn't complete stable, I can
estimate remaining temperature oscillations to an amount of about 20
mK (usually this is no problem). Now I fear, that due to the
remaining temperature oscillations the line form of the
exchange broadened signals becomes modulated in such a manner
that in a last result I see T1 noise. I have not enough experience
within the field of DNMR to validate this assumption.
Could this be reasonable?
Best regards
Rainer Haessner
(http://www.org.chemie.tu-muenchen.de/people/rh/
http://www.nmr.de)