High resolution solid-state NMR on the desktop

High-resolution low-field nuclear magnetic resonance (NMR) spectroscopy has found wide application for characterization of liquid compounds because of the low maintenance cost of modern permanent magnets. Solidstate NMR so far is limited to low-resolution measurements of static powders, because of the limited space available in this type of magnet. Magic-angle sample spinning and low-magnetic fields are an attractive combination to achieve high spectral resolution especially for paramagnetic solids. Here we show that magic angle spinning modules can be miniaturized using 3D printing techniques so that high-resolution solid-state NMR in permanent magnets becomes possible. The suggested conical rotor design was developed using finite element calculations and provides sample spinning frequencies higher than 20 kHz. The setup was tested on various diamagnetic and paramagnetic compounds including paramagnetic battery materials. The only comparable experiments in low-cost magnets known so far, had been done in the early times of magic angle spinning using electromagnets at much lower sample spinning frequency. Our results demonstrate that high-resolution low-field magic-angle-spinning NMR does not require expensive superconducting magnets and that high-resolution solidstate NMR spectra of paramagnetic compounds are feasible. Generally, this could introduce low-field solid-state NMR for abundant nuclei standard as a routine analytical tool.

Automated summary

Low-field high-resolution nuclear magnetic resonance (NMR) spectroscopy is commonly used for liquid compound characterization due to its low maintenance cost. However, solid-state NMR is limited to low-resolution measurements of static powders. In this study, we miniaturize the magic-angle-spinning modules using 3D printing techniques, allowing high-resolution solid-state NMR in permanent magnets. Our results demonstrate that expensive superconducting magnets are not required for high-resolution low-field magic-angle-spinning NMR, making it feasible for the analysis of paramagnetic compounds.