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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 ? enter image description here

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    $\begingroup$ You should repeat the solvent suppression experiment with different values of O1P, generally this needs to be optimised in order to get the best suppression — it's not necessarily just the frequency at the top of the water peak. $\endgroup$
    – orthocresol
    Commented May 7, 2023 at 15:06
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    $\begingroup$ I am not familiar with "zgpurge" specifically (you may want to explain in more detail what kind of suppression it involves). $\endgroup$
    – Buck Thorn ♦
    Commented May 7, 2023 at 17:13
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    $\begingroup$ In my experience, even if you achieve good suppression, the phase of the water peak can vary by quite a bit. Just google for 'water suppression nmr' and you'll see plenty of examples, this was the first one I found. I don't know exactly why this is the case, but radiation damping seems like a reasonable guess. In any case, I think it's quite normal to have an out-of-phase H2O peak, and I don't think that your proposed solution will reliably work. $\endgroup$
    – orthocresol
    Commented May 7, 2023 at 17:18
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    $\begingroup$ (Btw, if you can sit at the spectrometer, it doesn't take very long to manually optimise one parameter (O1P) using the gs command. Optimising multiple parameters is a bit harder—as it turns out, I have a paper on this exact topic, which may or may not be interesting—but it might not be necessary at all depending on your use case and what the pulse sequence does. I agree with @BuckThorn that more details about the sequence would be useful; and I think Buck may know more about it than me anyway. ;)) $\endgroup$
    – orthocresol
    Commented May 7, 2023 at 17:26
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    $\begingroup$ Note this has been asked before here. You may edit the original post to include the pulseprogram but it suffices to include a description or reference $\endgroup$
    – Buck Thorn ♦
    Commented May 8, 2023 at 19:02

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