Homogeneous NMR spectra in inhomogeneous fields

Abstract

Researchers interested in high-resolution nuclear magnetic resonance (NMR) spectroscopy have long sought higher magnetic fields to enhance resolution and simplify spectra. Magnets with substantially larger fields than those available in the best commercial spectrometers are available, but the inhomogeneity is unacceptable for high-resolution spectra. A detection method (termed HOMOGENIZED) is presented that removes inhomogeneity while retaining chemical shift differences and J couplings. With existing inhomogeneous magnets, this method could nearly double the largest resonance frequency available for high-resolution NMR. The HOMOGENIZED sequence is based on observations of intermolecular zero-quantum coherences between a solute molecule and solvent molecules that are micrometers away; as long as the field is homogeneous over this short distance, sharp resonances are recovered without echoes. Experimental demonstrations and a detailed density matrix theory to explain the effect are presented.