Dear community,
I am currently running some solvent suppression experiment on water samples. I first run a one scan 1H experiment to get the ''O1P'' and then implement it in the solvent suppression experiment (''zgpurge'' pulse program). However the water signal appears distorted, it is asymmetrical and most likely unphased (other signals appear completly fine), which results in an inefficient solvent suppression experiment. I tried to overcome the problem by performing a 3D shimming, and adjusting the phasing parameters (Autophase during the lock and calibrated the autophase offset) but the problem persisted.
What could be the origin of the problem ?
Dear Samlem,
normally this sequence should wipe out the water nearly completely. Are the gradients working properly (at all)?
For a quick check I always use zggpw5 pulse sequence....without presat...
Alfred
Dear Alfred Ross
Many thanks for your answer. Are you referring to ''zggpw5'' pulse sequence to wipe out the water or to check for the proper working of the gradients ?
I tried the ''zggpw5'' pulse sequence and did not obtain any signal at all ! (as you can see in the attached image
...I use zggpw5 for solvent supression. I hope the probe is matchend and tuned and pulses are set properly. You need to specify a delay of the w5 (look in the sequence!) The spectrum enclosed looks as if gradients and the pulse sequence works perfectly well....there is a small signal to the right (which ppm?). In case of doubt you may want to place the sucrose reference (should be available at any NMR machine)...and compare the zggpw5 spectrum obtained with one obtained with zgpr sequence...
Good luck
Alfred
Dear Alfred Ross
The probe is perfectly fine as I replicated most of the tests that have been run by the installation technician, all the specifications have been met !
The pulse sequence I usually use in order to perform water signal suppression is ''zgpurge'', it worked just fine, until I met that very odd water signal shape as when I introduce the ''O1P'' got from the one scan 1H spectrum, the suppression was not really efficient (as if another signal appeared) ! So, for now I am trying to figure out the origin of that distorted water peak (knowing that all the quality control tests have been successfully done).
This said I tried, the ''Zggpw5'' pulse sequence and I have to say that in this specific situation (distorted water signal) it is more efficient than the ''zgpurge'' sequence.
Thank you very much for you feedback.
Sometimes, but rarely a NMR tube can be the problem. You may want to change the sample to another tube....
Alfred
I suspect this issue is related to the gradients. I would decrease the gradient strength and, or the delay after the gradient(s) to see if the resonance shape near the baseline becomes more symmetrical.
Residual vibrations caused by eddy currents contain anharmonic vibrations. The discrete FT requires the decay of all time-domain signals to be pure exponentials. But residual eddy current vibrations contain components that decay with with nonharmonic, nonperiodic modulation. The DFT can not accurately model these anharmonic signals. The problem isn’t the eddy currents, it’s that the DFT mathematically processes the anharmonic components as if they were harmonics.
The result is often an artifact in the wings of the frequency domain water-signal baseline similar to the one in your figure. Details about the impact of nonharmonic, nonperiodic water signal components can be found here: “High dynamic-range magnetic resonance spectroscopy (MRS) time-domain signal analysis.” Hutton, W. C.; Bretthorst, G. L.; Garbow, J. R.; Ackerman, J. J., Magn Reson Med, (2009) 62, pp 1026-35.
- Badges
- Science topic
- Similar topics
- Phytochemistry
- Extracts