A miniaturized spectrometer for NMR relaxometry under extreme conditions

NMRduino: A modular, open-source, low-field magnetic resonance platform

The NMRduino is a compact, cost-effective, sub-MHz NMR spectrometer that utilizes readily available open-source hardware and software components. One of its aims is to simplify the processes of instrument setup and data acquisition control to make experimental NMR spectroscopy accessible to a broader audience. In this introductory paper, the key features and potential applications of NMRduino are described to highlight its versatility both for research and education.

NMR Relaxation of Gas Adsorbed in Microporous Material

NMR relaxometry has been widely applied to characterize fluid confined in porous media because of its versatility, chemical selectivity, and noninvasive nature. Here we extend its usage to gas adsorbed in microporous materials by establishing a new quantitative model based on the molecular level NMR relaxation mechanism revealed by the molecular simulation of a prototypical adsorption system, CH4 adsorbed in ZIF-8. The model enables new NMR relaxometry-based characterization methods for thermodynamic, dynamic, and structural properties of adsorption systems, as demonstrated and validated by the experiments where the adsorption capacity and self-diffusivity of H2, CH4, and small alcohols adsorbed in ZIF-8 are deduced from the NMR relaxation data. The findings can serve for a better understanding of the composition-structure-properties relationships of a wide range of adsorption systems which is essential for the development and application of new functional microporous materials.

Refined high-pressure tube design for improved resolution in high-pressure NMR spectroscopy

A simple, low-cost, and easy-to-replicate high-pressure sapphire tube for NMR spectroscopy experiments is introduced. The significant improvement in spectral resolution enables, e.g., in situ quantification of the H2 ingress in green solvents.

Versatile high-pressure gas apparatus for benchtop NMR: Design and selected applications

A simple, yet highly versatile setup is presented for benchtop NMR analyses of gases at high-pressure. It consists mostly of commercial parts and includes multiple safety features while maintaining a small size to fit into a 1.20 m wide fume hood. Pressures up to 200 bar can be adjusted independently of the sample gas-bottle pressure in a matter of seconds. Mixtures of multiple gases can be produced in situ in a mixing chamber, which also serves to adjust the pressure. The high-pressure hardware and benchtop NMR spectrometer have been tested for long-term stability and repeatability of the measurements. The versatility of the setup is demonstrated by analyzing hydrocarbon-gas with attention to linewidths as well as their ¹H relaxation times, by improving the resolution of ¹H NMR spectra from solid polymers with pressurized CO₂, and by visualizing the ingress of gaseous and supercritical methane into liquid benzene.

Perspectives in process analytics using low field NMR

Low field NMR is a powerful analytical tool which creates an enormous added value in process analytics. Based on specific applications in process analytics and perspectives for low field NMR in form of spectroscopy, relaxation, diffusion, and imaging in quality control, diverse applications and technical realizations like spectrometers, time domain NMR, mobile NMR sensors and MRI will be discussed.

Low-field NMR relaxation-exchange measurements for the study of gas admission in microporous solids

Understanding the uptake and storage of gases by microporous materials is important for our future energy security. As such, we demonstrate here the application of two-dimensional NMR relaxation experiments for probing the admission and corresponding exchange dynamics of methane within microporous zeolites. Specifically, we report low-field (12.7 MHz) 1H NMR relaxation-exchange correlation measurements of methane within commercial LTA zeolites (3A and 4A) at 25 and 35 bar and ambient temperature. Our results demonstrate the clear identification of bulk-pore and pore-pore exchange processes within zeolite 4A, facilitating the calculation and comparison of effective exchange rate dynamics across varying diffusion length scales and gas pressures. Additional data acquired for zeolite 3A reveals the sensitivity of NMR relaxation phenomena to size-exclusive gas admission phenomena, illustrating the potential of benchtop NMR protocols for material screening applications.

Realtime optimization of multidimensional NMR spectroscopy on embedded sensing devices

The increasingly ubiquitous use of embedded devices calls for autonomous optimizations of sensor performance with meager computing resources. Due to the heavy computing needs, such optimization is rarely performed, and almost never carried out on-the-fly, resulting in a vast underutilization of deployed assets. Aiming at improving the measurement efficiency, we show an OED (Optimal Experimental Design) routine where quantities of interest of probable samples are partitioned into distinctive classes, with the corresponding sensor signals learned by supervised learning models. The trained models, digesting the compressed live data, are subsequently executed at the constrained device for continuous classification and optimization of measurements. We demonstrate the closed-loop method with multidimensional NMR (Nuclear Magnetic Resonance) relaxometry, an analytical technique seeing a substantial growth of field applications in recent years, on a wide range of complex fluids. The realtime portion of the procedure demands minimal computing load, and is ideally suited for instruments that are widely used in remote sensing and IoT networks.