Absolute quantification of Na+ bound fraction by double-quantum filtered 23Na NMR spectroscopy

A method is described for the absolute quantification of double-quantum filtered spectra of spin-3/2 nuclei (23Na). The method was tested on a model system, a cationic exchange resin for which the number of Na+ binding sites was quantitatively controlled. The theoretical and experimental approaches were validated on samples with different Na+ concentrations. An excellent agreement between the results obtained by double-quantum and single-quantum acquisitions was found. This method paves the way for absolute quantification of both bound and free fractions of Na+, which are determining factors in the characterization of salted/brined/dried food products.