Correlation of high-field and zero- to ultralow-field NMR properties using 2D spectroscopy

Abstract: The field of zero- to ultralow-field (ZULF) nuclear magnetic resonance (NMR) is currently experiencing a rapid growth, owing to the progress in optical magnetometry, and also attractive features of ZULF NMR, such as low hardware cost and excellent spectral resolution achieved under ZULF conditions. In this work, an approach is proposed and demonstrated for simultaneous acquisition of ZULF-NMR spectra of individual 13C-containing isotopomers of chemical compounds in a complex mixture. The method makes use of fast field cycling, so that the spin evolution takes place at ZULF conditions, whereas signal detection is performed in a high-field NMR spectrometer. This method has excellent sensitivity, also allowing easy assignment of ZULF-NMR spectra to specific analytes in the mixture. We demonstrate that the spectral information is the same as that given by ZULF-NMR, which makes the method suitable for creating a library of ZULF-NMR spectra of various compounds and their isotopomers. The results of the field-cycling experiments can be presented in a convenient way as 2D-NMR spectra with the direct detection giving the high-field 13C-NMR spectrum (carrying the chemical-shift information) and the indirect dimension giving the ZULF-NMR spectrum (containing information about proton-carbon J-couplings). Hence, the method can be seen as a variant of heteronuclear J-resolved spectroscopy, one of the first 2D-NMR techniques.