A Low‐Temperature Broadband NMR Probe for Multinuclear Cross‐Polarization

Dissolution dynamic nuclear polarization (D‐DNP) probes are usually designed for one or at most two specific nuclei. Investigation of multiple nuclei usually requires manufacturing a number of costly probes. In addition, changing the probe is a time‐consuming process since a system that works at low temperature (usually between 1.2 and 4.2 K) must be warmed up, thus increasing the risks of contamination. Here, an efficient apparatus is described for D‐DNP designed not only for microwave‐enhanced direct observation of a wide range of nuclei S such as 1H, 13C, 2H, 23Na, and 17O, but also for cross‐polarization (CP) from I=1H to such S nuclei. Unlike most conventional designs, the tuning and matching circuits are partly immersed in superfluid helium at temperatures down to 1.2 K. Intense radio‐frequency (RF) fields with amplitudes on the order of 50 kHz or better can be applied simultaneously to both nuclei I and S using RF amplifiers with powers on the order of 90 and 80 W, respectively, without significant losses of liquid helium. The system can operate at temperatures over a wide range between 1.2 and 300 K. One for many! An efficient broadband double‐resonance D‐DNP probe is described. This apparatus was used to detect NMR spectra of 1H, 23Na, 13C, 2H, and 17O with direct polarization. Additionally, 13C and 17O signals were also detected with cross polarization from 1H.