66. Detecting Low Concentrations of Unsaturated C-C Bonds by Parahydrogen-Induced Polarization using an Efficient Home-Built Parahydrogen Generator
Parahydrogen is a potentially significant source of hyperpolarization. However, a heat exchanger at an ultra-low temperature, which is normally sustained wastefully using liquid nitrogen, is essential for the generation of hyperpolarized parahydrogen. In order to cut down on the use of liquid nitrogen, we employed a cryogenic storage dewar as the key component of our home-built parahydrogen generator, which lasted over 20 d with a single filling. Small concentrations of an unsaturated compound in a mixture were identified by hydrogenation in a principle-based experiment involving the use of hyperpolarization and phase difference. Less than 1 µL of styrene in 1 mL of chloroform was identified in a single scan with a 43 MHz benchtop nuclear magnetic resonance (NMR) spectrometer following hydrogenation with 50% parahydrogen. This method can potentially undergo a significant development through the use of high-field NMR techniques, higher parahydrogen concentrations, and increased scan times for data collection, among others. Since hydrogenation with parahydrogen induces a phase reversal during attachment to unsaturated C-C bonds, it may be possible to detect many other unsaturated bonds in organic molecules. All in all, this study not only broadens the research on parahydrogen-based unsaturated-bond detection, but also facilitates the use of hyperpolarization by a broader range of researchers through the introduction of a long-lasting home-built parahydrogen generator.