Oh, Sugar
I have good news! With a minimal simplification of my INADEQUATE filter I have been able to rescue the last cross-peak of cholesterol. It had been rejected because too near to the diagonal. I changed the code saying: "if it's on the diagonal, it is bad; if it's just near, let's accept it". So it is possible to have the perfect INADEQUATE of cholesterol, with all the expected cross-peaks IN and everything else OUT.
Yesterday I received another INADEQUATE spectrum, this time of sucrose. The S/N is still high enough to make my filter unnecessary. If I play with the contour plot all the noise disappears while the 12 carbon atoms and their 10 bonds remain. Only a spurious peak remains at the coordinates 103.7;-22.9. I have not received the 1-D external projection, so I created it artificially. The spectral width is the same in both dimension (instead of being doubled for the DQF axis). The consequence is that two cross-peaks fall just on the boundary and are partially folded. This is the spectrum:
I have applied the filter with the same parameters used for the cholesterol (C-C coupling; linewidths in the two dimensions) while the threshold corresponds to the above plot. The result is perfect. All the cross-peaks are resolved and they are all present. Nothing else survives.
This time all the peaks are regular anti-phase doublets. The
Js are generally larger than in cholesterol.
Click on the thumbnails to see the full-size pictures. There is an expansion to help counting the correct number of cross-peaks.
Do you want to send another spectrum? I can clean it for free. Remember to enclose the 13-C of the same sample.
Source:
NMR Software blog