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In NMR and MRI, shimming is used prior to the operation of the magnet to eliminate inhomogeneities in its field. Initially, the magnetic field inside an NMR spectrometer or MRI scanner will be far from homogeneous compared with an "ideal" field of the device. This is a result of production tolerances and of the magnetic field of the environment.
In nuclear magnetic resonance spectroscopy, "shimming an NMR magnet" is a procedure to generate homogeneous magnetic field along the sample volume to obtain pure Lorentzian line shapes of various resonances in the spectrum. This is accomplished by manual shimming of individual shims, or automatic shimming procedure. [5]
Nuclear magnetic resonance crystallography (NMR crystallography) is a method which utilizes primarily NMR spectroscopy to determine the structure of solid materials on the atomic scale. Thus, solid-state NMR spectroscopy would be used primarily, possibly supplemented by quantum chemistry calculations (e.g. density functional theory ), [ 1 ...
A 900 MHz NMR instrument with a 21.1 T magnet at HWB-NMR, Birmingham, UK. Nuclear magnetic resonance spectroscopy, most commonly known as NMR spectroscopy or magnetic resonance spectroscopy (MRS), is a spectroscopic technique based on re-orientation of atomic nuclei with non-zero nuclear spins in an external magnetic field.
[1] [2] Although most NMR measurements are conducted on diamagnetic compounds, paramagnetic samples are also amenable to analysis and give rise to special effects indicated by a wide chemical shift range and broadened signals. Paramagnetism diminishes the resolution of an NMR spectrum to the extent that coupling is rarely resolved.
Free induction decay (FID) nuclear magnetic resonance signal seen from a well shimmed sample. In Fourier transform nuclear magnetic resonance spectroscopy, free induction decay (FID) is the observable nuclear magnetic resonance (NMR) signal generated by non-equilibrium nuclear spin magnetization precessing about the magnetic field (conventionally along z).
Chemical shift δ is usually expressed in parts per million (ppm) by frequency, because it is calculated from [5] =, where ν sample is the absolute resonance frequency of the sample, and ν ref is the absolute resonance frequency of a standard reference compound, measured in the same applied magnetic field B 0.
Nuclear magnetic resonance chemical shift re-referencing is a chemical analysis method for chemical shift referencing in biomolecular nuclear magnetic resonance (NMR). [1] It has been estimated that up to 20% of 13C and up to 35% of 15N shift assignments are improperly referenced.