High-resolution NMR spectroscopy in inhomogeneous fields via Hadamard-encoded intermolecular double-quantum coherences.

A new pulse sequence based on intermolecular double-quantum coherences was proposed to obtain one-dimensional high-resolution liquid NMR spectra in inhomogeneous magnetic fields via Hadamard encoding. In contrast with the conventional intermolecular multiple-quantum coherences method with a two-dimensional acquisition to obtain one one-dimensional high-resolution spectrum, the new method can provide relatively high-resolution spectra directly through one-dimensional acquisition, and can greatly improve the signal-to-noise ratio of the spectrum within a relatively short acquisition time. Theoretical derivation was performed and analytical expressions of the resulting signals are given. Solution samples in purposely de-shimmed magnetic fields and pig brain tissue samples were tested. The experimental results demonstrate that this sequence can retain useful structural information, even when the field inhomogeneity is sufficiently severe to erase almost all spectral information with conventional one-dimensional single-quantum coherence techniques, and good solvent suppression can be achieved. This method may provide a promising technique for applications in in vivo and in vitro NMR.