Two-dimensional high-resolution NMR spectra in matched b0 and b1 field gradients Page: 3 of 22
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The analytical information content of an NMR spectrum is related to the number of
lines that can be distinguished for a given bandwidth and under given experimental
conditions. Typically, the most useful spectral parameter is the chemical shift, so it is
desirable to use a homogeneous external field in order to produce a high chemical shift
resolution. However, for many applications, it would be convenient if a mobile magnet could
be scanned over the surface of an otherwise unaccessible object or subject in order to obtain
magnetic resonance information. Indeed, in the last decade, much effort has been put into the
development of surface NMR spectrometers (1, 2) for applications like well logging (3),
materials science (4) and biomedicine (5). The main drawback of such ex-situ NMR
spectroscopy is the large inhomogeneity of the magnetic field produced by a surface scanner.
The detection sensitivity can be enhanced by the use of Carr-Purcell echo trains (3, 6), which
refocus not only the effect of the field inhomogeneity but also the chemical shift information.
Therefore, the information content of ex-situ NMR spectroscopy has been limited to
relaxation parameters (7) and multiquantum buildup curves (8) in order to discriminate
between different material domains, whereas chemical shifts are typically not resolved in such
,,ex situ" spectrometers. Recently, a research group used matched gradients of the magnetic
field and rf-field in order to generate so-called nutation echoes and to apply them for
localized NMR spectroscopy (9, 10).
In the past, various two-dimensional sequences for the elimination of line-broadening
due to inhomogeneous magnetic fields have been developed (11-16) which are based on
delayed acquisition (17) superimposed on coherence transfer echoes (18). Here, the indirect
dimension yields highly resolved spectra, but it displays only the differences between the
chemical shifts of the evolving coherences and the observed nuclei instead of the direct
chemical shifts. The relative chemical shifts of the nuclei can therefore only be extracted
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Heise, Henrike; Sakellariou, Dimitris; Meriles, Carlos A.; Moule, Adam & Pines, Alexander. Two-dimensional high-resolution NMR spectra in matched b0 and b1 field gradients, article, January 9, 2002; Berkeley, California. (digital.library.unt.edu/ark:/67531/metadc735878/m1/3/: accessed June 19, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.