Enhancing the detection of edges and non-differentiable points in an NMR spectrum using delayed-acquisition

Delayed-acquisition, which is a common technique for improving spectral resolution in Fourier transform based spectroscopies, typically relies upon differences in T₂ relaxation rates that are often due to underlying differences in dynamics and/or complexities of the spin systems being studied. After an acquisition delay, the broad signals from fast T₂-relaxing species are more suppressed relative to the sharp signals from slow T₂-relaxing species. In this paper, an alternative source of differential “dephasing” under delayed-acquisition is demonstrated that is based solely upon the mathematical properties of the line shape and is independent of the underlying spin dynamics and/or complexity. Signals associated with frequencies where the line shape either changes sharply and/or is non-differentiable at some finite order dephase at a much slower rate than those signals associated with frequencies where the line shape is smooth. Experiments employing delayed-acquisition to study interfaces in biphasic samples, to measure spatially-dependent longitudinal relaxation, and to highlight sharp features in NMR spectra are presented.