13C dynamic nuclear polarization : An alternative detector for recycled-flow NMR experiments

Static NMR experiments on insensitive nuclei (e.g., 13C) have been generally difficult because of low magnetogyric ratios and/or poor natural abundance, even at the highest magnetic fields available. One method of overcoming these sensitivity limitations is dynamic nuclear polarization (DNP), which can be utilized to enhance NMR signals relative to those obtained with static NMR detection. In this study, we report a recycled-flow DNP apparatus capable of monitoring 13C scalar-dominated enhancements 1−2 orders of magnitude greater than those obtainable using the conventional recycled-flow 13C NMR experiment. Specifically, a mixture of benzene and several chlorocarbons were continuously “recycled” through a 13C DNP spectrometer. Results indicate successful detection with the 13C DNP approach in scalar-dominated cases, where analytes could not be observed with conventional static or flow NMR detection in a reasonable length of time.