Development of a 13C-optimized 1.5-mm high temperature superconducting NMR probe

We report a 1.5-mm NMR probe based on high temperature superconductors operating at 14.1 T optimized for C-13 detection. The probe has a total sample volume of about 35 microliters (mu L) with an active volume of 20 mu L and provides exceptional mass sensitivity for C-13 detection. The probe also has excellent H-1 sensitivity and employs a H-2 lock; N-15 irradiation capability can be added in the future. The coils are cooled to about 20 K using a standard Agilent cryogenic refrigeration system, and the sample temperature is regulated near room temperature. The coil design considerations are discussed in detail. This probe is ideal for directly detected C-13 NMR experiments for natural products chemistry and metabolomics applications, for which 35 mu L is an optimal sample volume. The outstanding C-13 sensitivity of this probe allowed us to directly determine the C-13 connectivity on 1.1 mg of natural abundance histidine using an INADEQUATE experiment. We demonstrated the utility of this probe for C-13-based metabolomics using a synthetic mixture of common natural abundance metabolites whose concentrations ranged from 1 to 5 mM (40-200 nmol). (c) 2013 Elsevier Inc. All rights reserved.