How are FT-NMR spectrometers different from continuous wave spectrometers?
The spectrometer we’ve described throughout this handout are continuous wave spectrometers, where the radiofrequency energy is held constant, and the magnetic field strength is varied. Fourier Transform Spectrometers (FT) work by exciting all magnetically active nuclei at once and measuring the decay curve as energy is released as the nuclei relax back to the ground state. Each different type of hydrogen contributes to the interference pattern, similar to the way different notes contribute to a chord. Computer programs can work backwards and deduce the absorption frequency of each hydrogen that contributed to the total signal. All aspects of chemical shift, splitting, number of unique hydrogens, etc., are all the same, for FT-NMR and for continuous wave. 10. What advantages do FT-NMR spectrometers offer over continuous wave instruments? Spectra of nuclei that are in low abundance or samples that are very dilute can be scanned rapidly and repeatedly until a decent spectrum is obtained.
