how to do the water suppression with proper phase correction for proton NMR in CD3OH ?
Here I am following presaturation method for water suppression.My sample is a Peptide.
I am getting huge negative phase of water after performing the experiment with the pulse program zgpr.
Need Proper solution to overcome this problem.
To correct phase: If you're using topspin software, then go to "adjust phase", set the "pivot point" by "right click n selection" at mid-point of your water peak. Then you try to adjust by dragging the "0" button. By the time you'll see other peaks would also need phase correction. Then you drag "1" button to up/down way and adjust. By repeating this process you can correct all the phases.
To suppress water peak: I would strongly recommend you don't do it. I know people who have lost their Ph.D. degree because of that.
Using water suppression is perfectly fine (and sometimes absolutely necessary), but you might lose some signals close to the water peak as well.
If you get a large negative peak with presaturation, the pulse is probably too strong.
Lower pl9 (or PLW9) in Watt or increase it in dB until you don't see a negative signal anymore.
It might also be that the offset is not determined accurately enough. There is a step-by-step guide to various solvent suppression techniques in the "1D and 2D step-by-step - Advanced" manual included in the topspin installation
You can find it by clicking the question mark to the top right in topspin and then clicking on manuals and selecting "1D and 2D step-by-step - Advanced" from the list that opens.
You can also find the manuals at https://www.bruker.com/service/information-communication/user-manuals/nmr.html (you can register for free), You want the "TopSpin Advanced NMR Experiments" manual.
Completely agree with Jani, there is nothing wrong with water peak suppression (especially in D2O) as long as you understand what you are doing and how it may affect your spectrum.
His comments on pulse power and irradiation frequency are very reasonable as well, so perhaps his advice is worth following (I don't use topspin myself, so cannot comment on step-by-step instructions).
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