nuclear magnetic resonance abbr., NMR (rus. ядерный магнитный резонанс abbr., ЯМР) — Resonance absorption of the radiofrequency electromahnetic waves by a substance with the non-zero nuclear spin of an atom in the external magnetic field.

Description

In a constant magnetic field nuclei with the non-zero nuclear spin undergo the splitting of energy levels (the Zeeman effect, see Fig.). The splitting energy and, thus, the resonant frequency are determined by the nature of the atomic nucleus, electronic environment and intra-and intermolecular interactions 1H, 13C, 15N, 19F, 29Si, 31P, etc. are examples of nuclei where resonance can be observed.

NMR serves as basis for NMR spectroscopy and magnetic resonance imaging (MRI). In all methods, the objects under analysis are placed in a strong constant magnetic field (up to 7 T in case of MRI and up to 22 T in NMR spectroscopy). The main challenge in the application of the methods is to analyse samples with ferromagnetism.

NMR spectroscopy is an important method for determining the molecular and supramolecular structures of various substances. The range of materials is very wide and includes inorganic, organic and bioorganic items, provided they have nuclei with the nonzero nuclear spin. NMR spectroscopy can be liquid (liquid or dissolved samples) and solid-state (solid, viscous and other samples with lower molecular and atomic mobility).

Liquid NMR spectroscopy is widely used to analyse various organic and bioorganic compounds, as it makes it relatively easy to obtain high resolution spectra. The most commonly used liquid NMR spectroscopy is that based on 1H (proton magnetic resonance, or PMR) as it is one of the most common and sensitive nuclei. Slightly less common is the liquid NMR spectroscopy based on 19F, 13C, 15N, and some others. Solid-state NMR spectroscopy as an analytical method found application after special hardware (MAS - magic angle spinning) and spectral methods were developed, which enabled high-resolution spectra of solid and viscous samples. In general, solid-state NMR spectroscopy in comparison with that of liquid has a lower resolution but much more sensitive as the sample are not diluted. The most commonly used solid-state NMR spectroscopy is based on 3C, 15N, 19F, 31P, 29Si, 27Al, etc., whereas high-resolution spectrum from 1H NMR spectroscopy is difficult due to strong dipole-dipole interactions between the nuclei.

In nanotechnology, NMR is used as a method for studying the structure of various materials, including composites, ceramics, polymers, heterogeneous catalysts, biological matters, etc. The NMR method can be used for detecting internal defects in the samples, studying various dynamic processes such as chemical reactions, phase transitions, etc.

Illustrations

Zeeman splitting of nucleus energies in a magnet field if nuclear spin I = 1/2.
Zeeman splitting of nucleus energies in a magnet field if nuclear spin I = 1/2.

Authors

  • Streletskiy Alexey V.
  • Kolyagin Yuriy G.

Source

  1. D. Brandon, W. Kaplan. Microstructural Characterization of Materials . — Wiley, 2008. — 550p.

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