Trace analysis in water‐alcohol mixtures by continuous p‐H2 hyperpolarization at high magnetic field

Nuclear magnetic resonance (NMR) studies of complex mixtures are often limited by the low sensitivity of the technique and by spectral overlap. We have recently reported on an NMR chemosensor on the basis of para‐Hydrogen Induced Polarization that potentially addresses both these issues, albeit for specific classes of compounds. This approach makes use of Signal Amplification By Reversible Exchange (SABRE) catalysts in methanol and allows selective detection and quantification of dilute analytes in complex mixtures. Herein, we demonstrate that, despite a large decrease in attained hyperpolarization, this method can be extended to water–alcohol mixtures. Our approach was tested on whisky, where nitrogenous heterocyclic flavor components at low‐micromolar concentration could be detected and quantified. PHIP NMR chemosensors based on SABRE catalysts have been recently proposed as a tool to detect specific analytes in complex mixtures in methanol. Here, we extend this method to water–alcohol mixtures and demonstrate the possibility to quantitatively determine dilute SABRE substrates, despite the large decrease in attained hyperpolarization due to the presence of water as co‐solvent. Our approach was tested on whisky, where nitrogenous heterocyclic flavor components at low‐micromolar concentration could be detected and quantified.