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Friday, November 2, 2007

FID Truncation and Spectral Distortion

Have you ever seen a spectrum like the one in the lower trace of the figure below?
This sin(x)/x distortion at the base of an NMR line is the result of truncation of the FID. The acquisition time was not long enough to capture the entire time domain signal. In addition to the distortion at the base of the lines, there is also a loss in spectral resolution as "sharp" features in a spectrum are defined by later times in the free induction decays. If you see this, you should re-run your spectrum with a longer acquisition time. If you do not have the option of re-running the spectrum, increase the line broadening (LB) and re-transform the data. This will get rid of the distortion but will not help with the resolution.

2 comments:

carlos said...

In principle it should be possible to get rid of the sinc wiggles while improving the resolution by using the Lorentz-to-Gauss transformation.

A better approach would involve applying the standard line broadening exponential weighting function followed by a second order derivative function.

By the way, congratulations for your blog, it's an excellent resource!

Arvin said...

Another option is to do Forward linear prediction and try to predict out the missing tail of the FID.