Hi there,
I am interpreting a HCcH-tocsy experiment for the first time and believe that my spectra requires calibration. It seems that my peaks are not located on the diagonal (shown in the image below) and am looking for a way to adjust this.
Many thanks!
Tyler
Hi Tyler,
sorry nobody’s got back to you on this yet. And I see we don’t have any decent documentation on this kind of thing yet, either - added to the ToDo list!
Essentially there are three ways you can change your Spectrum referencing/calibration:
Go to Spectrum Properties (double-click on your spectrum in the sidebar) and then to the Dimensions tab.
Change the Referencing (ppm) values by as much as required to shift the spectrum to where you want it to be. (Or occasionally it might be appropriate to change the Referencing (points) values.)
If you have two peaks in two Spectra which you know should be in the same position, then you can select them both and then right-click on one of them and select Calibrate Spectra from Peaks …. You’ll get a pop-up in which you can set which dimensions you want to shift so that the peaks overlap and check at the top which Peak/Spectrum is the one that will remain fixed/stationary.
Right-click on your spectrum and select Calibrate Spectra. You’ll get some blue marks which you can move. Once you start moving them you’ll see that there are in fact two sets of marks: one which is solid and one that is dashed. Place the solid marks on a current position and the dotted marks on the new position where you want that current position to move to (you can check using the values below). Change the Calibration by clicking on Apply for each relevant dimension. Then click Close to exit the Spectrum Calibration panel.
Which method you want to use to change/correct your Spectrum calibration will depend on your circumstances (and personal preferences). I find sometimes one method is more convenient and at other times another might be, it just depends. More often than not, though, I tend to use the second method.
Vicky
Those HCcH-TOCSY experiments (along with HcccoNH and some others) are often recorded with a phase incrementation trick that shifts the centre of the spectrum by 1/4 of the sweep width in the indirect 1H dimension. You should shift your reference point from the middle or edge of the spectrum by 1/4 of the total number of points to bring the diagonal back to x=y.
For future reference, this trick allows you to use a much narrrower 1H indirect sweep width so that you can get the same digital resolution in less time or better digital resolution in the same experimental time.
Best wishes
Brian
