NMR-spectrometers: overzicht

NMR spectrometers consist of a strong magnet, a radiofrequency or rf transmitter, and a detector attached to a computer console.

First-generation NMR instruments called continuous-wave spectrometers record spectra using the frequency-sweep or the field-sweep methods.

While resonance frequencies are determined by fixing the magnetic field strength and varying the rf signal in the former, the field strength is swept in the latter.

In modern pulsed Fourier-Transform-NMR or FT-NMR instruments, the magnetic field is held constant while the sample is irradiated with a series of short high-power rf pulses.

Pulses have a large frequency spread that can simultaneously excite NMR-active nuclei with a range of resonance frequencies.

In the interval or delay between pulses, the nuclei relax and return to their original state, releasing rf energy in the form of a free induction decay or FID signal.

The FID signals recorded by the detector are converted by a Fourier transformation into a frequency-versus-amplitude signal, which is the NMR spectrum.