Two-Dimensional High-Resolution NMR Spectra in Matched B0 and B1 Field Gradients

Abstract

In a recent publication we presented a method to obtain highly resolved NMR spectra in the presence of an inhomogeneous B0 field with the help of a matched RF gradient. If RF gradient pulses are combined with “ideal” 90° pulses to form inhomogeneous z rotation pulses, the line broadening caused by the B0 gradient can be refocused, while the full chemical shift information is maintained. This approach is of potential use for NMR spectroscopy in an inhomogeneous magnetic field produced by an “ex-situ” surface spectrometer. In this contribution, we extend this method toward two-dimensional spectroscopy with high resolution in one or both dimensions. Line narrowing in the indirect dimension can be achieved by two types of nutation echoes, thus leading to depth-sensitive NMR spectra with full chemical shift information. If the nutation echo in the indirect dimension is combined with a stroboscopic acquisition using inhomogeneous z-rotation pulses, highly resolved two-dimensional correlation spectra can be obtained in matched field gradients. Finally, we demonstrate that an INEPT coherence transfer from proton to carbon spins is possible in inhomogeneous B0 fields. Thus, it is possible to obtain one-dimensional 13C NMR spectra with increased sensitivity and two-dimensional HETCOR spectra in the presence of B0 gradients of 0.4 mT/cm. These schemes may be of some value for ex-situ NMR analysis of materials and biological systems.