Design of solenoidal microcoils for high-resolution 13C NMR spectroscopy

Typical high-resolution natural-abundance 13C NMR experiments require milligrams of material. In this study, solenoidal microcoil direct and inverse detection probes have been designed to explore improvements in the limits of detection (LOD) for 13C NMR at 11.7 T. A direct-detection radio frequency probe with an observe volume (Vobs) of 1 microL has been developed with carbon observe, deuterium lock, and proton decouple channels. The nonspinning line width of a decoupled [3-13C]-L-alanine (99%) peak achieved is 1.3 Hz. The natural-abundance 13C3 sigma LOD for sucrose for a 90-min acquisition time is 18 micrograms (52 nmol). The 3 sigma LOD for [3-13C]-L-alanine (99%) is 375 ng (4.2 nmol) for an acquisition time less than 30 s. The inverse detection probe has proton observe and carbon decouple channels and a Vobs of 550 nL. The 3 sigma LOD for sucrose from a 1 D 13C decoupled HMQC spectrum is 1.6 micrograms (4.5 nmol) for a 14-min acquisition time.