Abstract
This study develops the two-field correlation spectroscopy (COSY) in zero to ultralow field (ZULF) liquid state nuclear magnetic resonance (NMR). We demonstrated the successful integration of signal amplification by reversible exchange (SABRE) hyperpolarization with two-dimensional (2D) NMR spectroscopy, enabling the detection of ZULF COSY spectra with increased sensitivity. Field cycling allowed the acquisition of two-field COSY spectra at varying magnetic field strengths, including zero-field conditions. This enabled insight into both J-coupling and Zeeman-dominated regimes, benefiting from ultralow field observation sensitivity and mitigating the low-frequency noise by conducting readout at higher fields (>5 μT). Our study explores the effects of polarization transfer, apodization techniques, and the potential for further application of ZULF NMR in chemical analysis exemplified for three X-nuclei and three corresponding molecules: [1-(13)C]pyruvate, [(15)N]acetonitrile, and [3-(19)F]pyridine. These findings pave the way for more sensitive and cost-effective NMR spectroscopy in low-field regimes.