High resolution triple resonance micro magic angle spinning NMR spectroscopy of nanoliter sample volumes

To be able to study mass-limited samples and small single crystals, a triple resonance micro-magic angle spinning (mMAS) probehead for the application of high-resolution solid-state NMR of nanoliter samples was developed. Due to its excellent rf performance this allows us to explore the limits of proton NMR resolution in strongly coupled solids. Using homonuclear decoupling we obtain unprecedented H-1 linewidths for a single crystal of glycine (Delta nu(CH2) = 0.14 ppm) at high field (20 T) in a directly detected spectrum. The triple channel design allowed the recording of high-resolution mMAS C-13-N-15 correlations of [U-C-13-N-15] arginine HCl and shows that the superior 1H resolution opens the way for high-sensitivity inverse detection of heteronuclei even at moderate spinning speeds and rf-fields. Efficient decoupling leads to long coherence times which can be exploited in many correlation experiments.