Image Credit: Progression, Inc. | Oxford Instruments
NMR (Nuclear Magnetic Resonance) spectrometers are analytical devices that exploit the magnetic properties of certain atomic nuclei to determine physical and chemical properties of atoms or the molecules in which they are contained. These devices are the preferred means for determining and analyzing the structure of organic compounds.
NMR spectrometry involves subjecting an analyte to an applied magnetic field. This aligns (or polarizes) the magnetic nuclear spins of the different atoms in the compound. By inducing an electro-magnetic pulse through the substance, NMR spectrometers can read the frequency of the disturbance it caused in each individual atom. These observations, called chemical shifts, can then be interpreted to draw conclusions about the properties of analyte.
NMR spectrometers can be constructed as either benchtop or full-scale devices. Benchtop devices are convenient for quick measurements and are easier to use, requiring less sample preparation and configuration. Full scale devices are better suited for more detailed and in-depth analytical results.
Types of NMR Spectrometers
The continuous wave (CW) and the fourier transformation (FT) spectrometer are the two overarching types of NMR spectrometers.
Continuous wave spectrometers analyze the sample at a constant frequency of light while applying a sweeping magnetic field to achieve nuclei resonance. These spectrometers are less efficient than fourier transform spectrometers, since they read individual frequency responses in succession. They also suffer from a poor signal-to-noise ratio which can be mitigated through repeat measurements.
Fourier transorm spectrometers analyze the sample involving exciting the full NMR spectra by utilizing short monochromatic radio frequency pulses. These spectrometers are the standard for NMR spectrometers today, as they are more efficient and precise than continuous wave devices, but they are also more expensive.