Low-field and benchtop Nuclear Magnetic Resonance (NMR) spectrometers offer significant advantages in terms of cost and accessibility, but their widespread application is limited by their inherently low sensitivity. Hyperpolarisation techniques like Signal Amplification By Reversible Exchange (SABRE) can overcome this limitation by boosting NMR signals by several orders of magnitude, creating new opportunities for chemical analysis and process monitoring outside of specialist laboratories. However, to realise this potential, methods for generating and measuring hyperpolarised signals must be robust and reproducible.
This work details the development of an automated para-hydrogen gas flow system to enable the probing of polarisation transfer and relaxation dynamics in SABRE. The system was developed to overcome the limitations of ex situ measurements, with applications for both in situ ultra-low-field studies and experiments on benchtop NMR spectrometers. The system provides reproducible para-hydrogen delivery with precise control over experimental parameters, enabling time-resolved studies of the hyperpolarisation process.
Application of this system to a solution of SABRE catalyst and pyridine enabled the indirect observation of para-hydrogen spin-order relaxation at the Earth's field. The decay of the hyperpolarised signal followed a biexponential model, dominated by a fast relaxation process t≌1-4 s. This relaxation rate appears to be governed by the competitive exchange of ligands at the iridium catalyst, providing insight into the solution-state dynamics of para-hydrogen.
The utility and modularity of the polariser unit were further established by its integration with a 1.4 T benchtop spectrometer with an integrated motor-driven sample shuttle and capillary bubbling system. Software was developed for the motor system, spectrometer and user interface to make all components compatible for synchronous motor-driven polarisation transfer, bubbling and detection. This integrated hardware implementation demonstrates a viable pathway for performing advanced, automated SABRE experiments on accessible low-field platforms, moving beyond the limitations of manual sample handling.
