Objective: The aim was to develop a novel image processing protocol for confocal laser scanning microscopy (CLSM) to study mineral distribution within erosive lesions as a function of depth. Methods: Polished bovine enamel samples (n=80) were divided into groups (8/group) with similar mean surface microhardness (SMH) values. Samples underwent erosion (1% citric acid pH3.8) for 1,5,10,15, or 30min, with or without stirring giving 10 treatment groups in a 2*5 factorial design. SMH was used to measure erosive softening. Profilometry was used to measure bulk tissue loss. Samples were then stained with rhodamine-B (0.1mM, 24h) and imaged using CLSM. Image processing was used to measure fluorescence volume (FV) as a function of depth for each image. The data from reference images were subtracted from post-erosive data to determine changes in fluorescent volume (ΔFV) as a function of depth. 2-way ANOVA and linear regression analysis were used where applicable.Results: Surface softening and bulk tissue loss increased with acid erosion duration with or without stirring. Stirring significantly increased net softening at each time point; specimens underwent significantly more bulk tissue loss (P<0.05). CLSM showed the erosive lesion deepened as exposure to acid increased, and that at the near surface (0-10µm) FV and ΔFV increased rapidly for stirred solutions. The increase in pore space translated to a softer surface as measured by SMH. Conclusion:This novel non-destructive method allows concurrent quantification of dental erosion by mineral loss as a function of depth, and qualitative characterisation of microstructural changes during early erosion.

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Decarbonisation of the energy sector is becoming increasingly more important to the reduction in climate change. Renewable energy is an effective means of reducing CO2 emissions, but the fluctuation in demand and production of energy is a limiting factor. Liquid hydrogen allows for long-term storage of energy. Hydrogen quality is important for the safety and efficiency of the end user. Furthermore, the quality of the hydrogen gas after liquefaction has not yet been reported. The purity of hydrogen after liquefaction was assessed against the specification of Hydrogen grade D in the ISO-14687:2019 by analysing samples taken at different locations throughout production. Sampling was carried out directly in gas cylinders, and purity was assessed using multiple analytical methods. The results indicate that the hydrogen gas produced from liquefaction is of a higher purity than the starting gas, with all impurities below the threshold values set in ISO-14687:2019. The amount fraction of water measured in the hydrogen sample increased with repeated sampling from the liquid hydrogen tank, suggesting that the sampling system used was affected by low temperatures (−253 °C). These data demonstrate for the first time the impact of liquefaction on hydrogen purity assessed against ISO-14687:2019, showing that liquified hydrogen is a viable option for long-term energy storage whilst also improving quality.

Formic acid is an intermediate of the steam methane reforming process for hydrogen production. According to International Standard ISO 14687, the amount fraction level of formic acid present in the hydrogen supplied to fuel cell electric vehicles must not exceed 200 nmol.mol−1. The development of formic acid standards in hydrogen is crucial to validate the analytical results and ensure measurement reliability for the fuel cell electric vehicles industry. NPL demonstrated that these standards can be gravimetrically prepared and validated at 4 to 100 µmol.mol−1, with a shelf-life of 1 year (stability uncertainty < 7%; k = 2). Stability was not affected over 1 year or by low temperature or pressure. At sub-µmol.mol−1 level, formic acid amount fraction was found to decrease due to adsorption on the gas cylinder surface; however, it is possible to certify the formic acid amount fraction after a period of 20 days and ensure the certified value validity for 1 year with an uncertainty below 7% (k = 1) confirmed by thermodynamic investigation. This study demonstrated that formic acid in hydrogen gas reference materials can be prepared with reasonable uncertainty (>7%, k = 1) and shelf life (>1 year). Potential applications include the calibration of analysers and for studying the impact of formic acid on future application with relevant traceability and accuracy.