SABRE hyperpolarization enables high-sensitivity 1H and 13C benchtop NMR spectroscopy

Abstract

Benchtop NMR spectrometers operating with low magnetic fields of 1–2 T at sub-ppm resolution show great promise as analytical platforms that can be used outside the traditional laboratory environment for industrial process monitoring. One current limitation that reduces the uptake of benchtop NMR is associated with the detection fields’ reduced sensitivity. Here we demonstrate how para-hydrogen (p-H₂) based signal amplification by reversible exchange (SABRE), a simple to achieve hyperpolarization technique, enhances agent detectability within the environment of a benchtop (1 T) NMR spectrometer so that informative ¹H and ¹³C NMR spectra can be readily recorded for low-concentration analytes. SABRE-derived ¹H NMR signal enhancements of up to 17 000-fold, corresponding to ¹H polarization levels of P = 5.9%, were achieved for 26 mM pyridine in d₄-methanol in a matter of seconds. Comparable enhancement levels can be achieved in both deuterated and protio solvents but now the SABRE-enhanced analyte signals dominate due to the comparatively weak thermally-polarized solvent response. The SABRE approach also enables the acquisition of ¹³C NMR spectra of analytes at natural isotopic abundance in a single scan as evidenced by hyperpolarized ¹³C NMR spectra of tens of millimolar concentrations of 4-methylpyridine. Now the associated signal enhancement factors are up to 45 500 fold (P = 4.0%) and achieved in just 15 s. Integration of an automated SABRE polarization system with the benchtop NMR spectrometer framework produces renewable and reproducible NMR signal enhancements that can be exploited for the collection of multi-dimensional NMR spectra, exemplified here by a SABRE-enhanced 2D COSY NMR spectrum.