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How much is too much Apodization for an NMR FID?

September 5, 2008

For a structure elucidation process, applying an apodization (or window function) to an NMR spectrum can be a good thing and sometimes can be a bad thing. Making peaks broader can assist in differentiating signals from noise, but can also cause neighboring peaks to mesh into a single resonance. The best approach in handling spectral data is to consider an extra processing step and FT with minimal or no apodization.

The 13C NMR spectra below illustrates the effects of different numerical values for line broadening on two 13C resonances. At an exponential line broadening of 2 Hz, the two 13C resonances appear as a single resonance. The result is an underestimated carbon count. If no apodization is applied, the 2 carbon resonances are clearly visible.

13capodization_sept52008_2

TIP: FT an FID with and without line broadening and compare the results. This simple extra step can save loads of time when working on an elucidation problem.

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