Parahydrogen Based Hyperpolarization for Multinuclear NMR Spectroscopy in Ultra-Low Magnetic Fields
Ultra-low field (ULF) nuclear magnetic resonance (NMR) is a promising spectroscopy method allowing for, e.g., the simultaneous detection of multiple nuclei. To overcome the low signal-to-noise ratio that usually hampers a wider application, we used an alternative approach to ULF NMR, which makes use of the hyperpolarizing technique signal amplification by reversible exchange (SABRE). In contrast to standard parahydrogen hyperpolarization, SABRE can continuously hyperpolarize 1H as well as other MR-active nuclei. For simultaneous measurements of 1H and 19F under SABRE conditions a superconducting quantum interference device (SQUID)-based NMR detection unit was adapted. We successfully hyperpolarized fluorinated pyridine derivatives with an up to 2000-fold signal enhancement in 19F. SABRE combined with simultaneous SQUID-based broadband multinuclear detection enable the quantitative analysis of multinuclear processes.