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.

The Non-linear Electrical Properties of Silver/silver Chloride Electrodes in Sodium Chloride Solution

An electrical measurement is non-linear when it is affected by the applied stimulus, i.e. when the measured phenomenon changes with amplitude. If pinched hysteresis loops can be observed in the voltage current representation, the underlying tissue can be classified as a memristor. Several biological memristors have been published, like human skin and apples. However, changes in the polarization impedance of electrodes may also cause pinched hysteresis loops. The question whether the reported biological memristors are real or whether the results just reflect changes in the polarization impedance arises. If the impedance of the measured object is close to or smaller than the polarization impedance of the used electrodes, the latter may dominate the measurement. In this study, we investigated the non-linear electrical properties of silver/silver chloride electrodes in a sodium chloride solution that has a similar concentration as human sweat and compared these to results from human skin. First of all, we found that silver/silver chloride electrodes in sodium chloride solution can be classified as memristors. However, the currents obtained from the sodium chloride solution are much higher than the currents recorded from human skin and there is a qualitative difference in the pinched hysteresis loops in both cases. We can conclude that the non-linear electrical measurements with silver/silver chloride on human skin are actually dominated by the skin and we can confirm that the human skin memristor really exists.