Improved strategies for NMR diffusion measurements with magnetization-grating rotating-frame imaging (MAGROFI)

Abstract

The NMR measurement of molecular diffusion with magnetization-grating rotating-frame imaging (MAGROFI) is improved by utilizing the tightest magnetization grating that is but resolved by the imaging data (Nyquist grating). The tightness of a Nyquist grating depends on the digital image resolution, and a fixed relationship is found between grating preparation and rotating-frame imaging. If applied to toroid cavity NMR detectors, phase-cycled fast two-transient NYGROFI (Nyquist-grating rotating-frame imaging) reduces the experimental time to minutes or only seconds depending mainly on relaxation times. For the compensation of radiofrequency pulse deficiencies, gratings are prepared with a pulse train similar to the one used for data acquisition. The NYGROFI transients are supplemented by a saturation-recovery sequence to compensate for T₁ relaxation that inevitably occurs during the experiment. From a numerical finite-difference approach that simulates the effects of diffusion during both the evolution time and the pulse sequences, diffusion coefficients are accurately determined by fitting simulated nutation interferograms to experimental data. Diffusion coefficients of individual components in mixed systems are measured with a new difference spectroscopy technique.