Clinical-Scale Production of Nearly Pure (>98.5%) Parahydrogen and Quantification by Benchtop NMR Spectroscopy.

Abstract

Because of the extensive chemical, physical, and biomedical applications of parahydrogen, the need exists for the development of highly enriched parahydrogen in a robust and efficient manner. Herein, we present a parahydrogen enrichment equipment which substantially improves upon the previous generators with its ability to enrich parahydrogen to >98.5% and a production rate of up to 4 standard liters per minute with the added advantage of real-time quantification. Our generator employs a pulsed injection system with a 3/16 in. outside diameter copper spiral tubing filled with iron-oxide catalyst. This tubing is mated to a custom-made copper attachment to provide efficient thermal coupling to the cold head. This device allows for robust operation at high pressures up to 34 atm. Real-time quantification by benchtop NMR spectroscopy is made possible by direct coupling of the p-H2 outlet from the generator to a 1.4 T NMR spectrometer using a regular 5 mm NMR tube that is continuously refilled with the exiting parahydrogen gas at ∼8 atm pressure. The use of high hydrogen gas pressure offers two critical NMR signal detection benefits: increased concentration and line narrowing. Our work presents a comprehensive description of the apparatus for a convenient and robust parahydrogen production, distribution, and quantification system, especially for parahydrogen-based hyperpolarization NMR research.