Variation of the Overhauser Enhancement with Field-Cycling

Dynamic nuclear polarization (DNP) is an NMR-based technique which enables detection and spectral characterization of endogenous and exogenous paramagnetic substances measured as a transfer of polarization from the saturated unpaired electron spin system to the NMR active nuclei. In case of proton NMR the transfer of polarization leads to an enhancement of the detected proton signal called the Overhauser enhancement [1]. The electron irradiation and the NMR detection may occur at different magnetic field strengths in a DNP spectroscopy experiment. An evaluation of the variation in the Overhauser enhancement with increased separation between the electron irradiation field and the NMR detection field shows that the measured Overhauser enhancement decreases with increasing in field-cycling.