Design of Solenoidal Microcoils for High-Resolution 13C NMR Spectroscopy

Abstract

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 (V_obs) of 1 μL 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 ¹³C 3σ LOD for sucrose for a 90-min acquisition time is 18 μg (52 nmol). The 3σ 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 V_obs of 550 nL. The 3σ LOD for sucrose from a 1D ¹³C decoupled HMQC spectrum is 1.6 μg (4.5 nmol) for a 14-min acquisition time.