Stable isotope quality assurance using the 'Calibrated IRMS' strategy

Procedures in our laboratory have always been directed towards complete understanding of all processes involved and corrections needed etc., instead of relying fully on laboratory reference materials. This rather principal strategy (or attitude) is probably not optimal in the economic sense, and is not necessarily more accurate either. Still, it has proven to be very rewarding in its capability to detect caveats that go undiscovered in the standard way of measurement, but that do influence the accuracy or reliability of the measurement procedure. An additional benefit of our laboratory procedures is that it makes us capable of assisting the International Atomic Energy Agency (IAEA) with primary questions like mutual scale assignments and comparison of isotope ratios of the same isotope in different matrices (like delta(18)O in water, carbonates and atmospheric CO(2)), establishment of the (17)O-(18)O relation, and the replenishment of the calibration standards. Finally, for manual preparation systems with a low sample throughput ( and thus only few reference materials analysed) it may well be the only way to produce reliable results

Ice-liquid isotope fractionation factors for O-18 and H-2 deduced from the isotopic correction constants for the triple point of water

The stable isotopes of water are extensively used as tracers in many fields of research. For this use, it is essential to know the isotope fractionation factors connected to various processes, the most important of which being phase changes. Many experimental studies have been performed on phase change fractionation over the last decades. Whereas liquid-vapour fractionation measurements are relatively straightforward, vapour-solid and liquid-solid fractionation measurements are more complicated, as maintaining equilibrium conditions when a solid is involved is difficult. In this work, we determine the ice-liquid isotope fractionation factors in an indirect way, by applying the Van't Hoff equation. This equation describes the relationship of the fractionation factors with isotope-dependent temperature changes. We apply it to the recently experimentally determined isotope dependences of the triple point temperature of water [Faghihi V, Peruzzi A, Aerts-Bijma AT, et al. Accurate experimental determination of the isotope effects on the triple point temperature of water. I. Dependence on the H-2 abundance. Metrologia. 2015;52:819-826; Faghihi V, Kozicki M, Aerts-Bijma AT, et al. Accurate experimental determination of the isotope effects on the triple point temperature of water. II. Combined dependence on the O-18 and O-17 abundances. Metrologia. 2015;52:827-834]. This results in new values for the H-2 (deuterium) and O-18 fractionation factors for the liquid-solid phase change of water, which agree well with existing, direct experimental data [Lehmann M, Siegenthaler U. Equilibrium oxygen- and hydrogen-isotope fractionation between ice and water. J Glaciol. 1991;37:23-26]. For H-2, the uncertainty is improved by a factor of 3, whereas for O-18 the uncertainty is similar. Our final results are (S-L) (H-2/H-1)=1.02093(13), and (S-L) (O-18/O-16)=1.002909(25), where the latter is the weighted average of the previous experimental study and this work

Absolute isotope ratios of carbon dioxide a feasibility study

One way of obtaining isotope ratios, traceable to the International System of Units, is the gravimetric isotope mixtures method. Adapting this method to carbon dioxide is challenging since measuring all twelve isotopologues at once with a gas mass spectrometer is currently not possible. The calculation of the mass bias correction factors is no straightforward task due to the fact that the isotopic equilibrium has to be considered. This publication demonstrates a potential way of adapting this method to carbon dioxide while considering isotope equilibrium. We also show how we prepared binary blends from enriched/depleted carbon dioxide parent gases and how equilibrating the different gases by heating affects the measurements. Furthermore, we reveal mathematical limitations of our approach when the gases are not in isotope equilibrium and which issues occur due to measurement limitations. In a simulation, using authentic data, we asses our approach in terms of achievable uncertainties and discuss further improvements, like using atomic spectroscopy methods

Association between Transcription Factor AP-2B genotype, obesity, insulin resistance and dietary intake in a longitudinal birth cohort study Transcription Factor AP-2B associated with obesity

This is a post-peer-review, pre-copyedit version of an article published in International Journal of Obesity.The development of obesity has a large genetic component, and the gene encoding the transcription factor 2 beta (TFAP2B) has been identified as one of the responsible factors. We investigated the effect of TFAP2B intron 2 variable number tandem repeat (VNTR) genotype on obesity, insulin resistance and dietary intake from 15 to 33 years of age

Designing a Locally Manufacturable Wheelchair for Nepal

Persons with disabilities in developing countries often lack the basic equipment needed to assist them in their daily lives. International Nepal Fellowship (INF) is a Christian medical organization located in Nepal that provides medical care and assistance to people with disabilities and other conditions. Currently, INF imports expensive wheelchairs that undergo a prolonged border process before being received. INF has reached out to the Collaboratory to design a wheelchair that can withstand the challenges of Nepal’s terrain and can be manufactured from local materials. The Nepal Wheelchair team accepted this challenge and set out to design a wheelchair that can fulfill their needs. The team began by researching wheelchair models for inspiration and eventually settled on two preliminary designs. In January 2020, the team traveled to Pokhara, Nepal to gain feedback from the staff at INF and select a final design based on their comments. During this trip, the team acquired and brought back locally available materials and parts available in Nepal in order to construct a prototype. This year, prototyping has been completed for the following elements: the central frame, wheel lock, footrest, wheel mounting assemblies and armrest fixtures. As a result of knowledge gained during prototyping, some design changes to the wheelchair have been made. Moving forward, the team will test the overall prototype for durability and prepare a manufacturing manual for INF.https://mosaic.messiah.edu/engr2021/1010/thumbnail.jp

Biogenic Carbon Fraction of Biogas and Natural Gas Fuel Mixtures Determined with 14C

This study investigates the accuracy of the radiocarbon-based calculation of the biogenic carbon fraction for different biogas and biofossil gas mixtures. The focus is on the uncertainty in the C-14 reference values for 100% biogenic carbon and on the C-13-based isotope fractionation correction of the measured C-14 values. The separately (AMS) measured CO2 and CH4 fractions of 8 different biogas samples showed C-14 values between 102% and 116% (pMC). The delta C-13 values of these samples varied between -6% and +31% for the CO2 fraction and between -28% and -62% for the CH4 fraction. The uncertainty in calculated biogenic carbon fractions due to uncertainty in the C-14 reference values depends on the available information about the origin of the used biogenic materials. It varies between +/- 0.5% and +/- 3.5% (absolute) depending on the type of biogas. A method is proposed to minimize this uncertainty for different groups of biogases. The calculated biogenic carbon fraction deviates up to +/- 2.5% for biofossil gas mixtures, if the applied isotope fractionation correction is based on the delta C-13 value of the mixed biofossil sample instead of the biogenic delta C-13 value. Combination of both error sources shows that the uncertainty in the calculated biogenic carbon fraction varies between +/- 0.7% and +/- 4.5%, depending on the type of biogas in the sample