In-Line Combustion System for the Measurement of δC-CH in Gas Reference Materials Using Optical Isotope Ratio Spectroscopy.

Measurements of the stable carbon isotope ratio in methane (δC-CH) are used in determining the source of CH emissions on local, regional, and global scales. To achieve the required level of data comparability for atmospheric monitoring networks, accurate gas reference materials of δC-CH in air are required with high levels of reproducibility. We describe a method to determine the δC-CH of CH in synthetic air reference materials reported against the Vienna Pee Dee Belemnite (VPDB) scale.

Stable Isotope Reference Materials and Scale Definitions-Outcomes of the 2024 IAEA Experts Meeting.

The participants of the 12 International Atomic Energy Agency (IAEA) meeting on stable isotope reference materials reached a consensus, acknowledging the existence and use of two carbon isotope delta scales: the VPDB (Vienna Peedee belemnite) scale and the VPDB-LSVEC (LSVEC - lithium carbonate prepared by H. J. Svec).

Characterization of Fourier Transform Infrared, Cavity Ring-Down Spectroscopy, and Optical Feedback Cavity-Enhanced Absorption Spectroscopy Instruments for the Analysis of Ammonia in Biogas and Biomethane.

Novel traceable analytical methods and reference gas standards were developed for the detection of trace-level ammonia in biogas and biomethane. This work focused on an ammonia amount fraction at an upper limit level of 10 mg m (corresponding to approximately 14 μmol mol) specified in EN 16723-1:2016. The application of spectroscopic analytical methods, such as Fourier transform infrared spectroscopy, cavity ring-down spectroscopy, and optical feedback cavity-enhanced absorption spectroscopy, was investigated.

Isotopically characterised N O reference materials for use as community standards.

Rationale: Information on the isotopic composition of nitrous oxide (N O) at natural abundance supports the identification of its source and sink processes. In recent years, a number of mass spectrometric and laser spectroscopic techniques have been developed and are increasingly used by the research community. Advances in this active research area, however, critically depend on the availability of suitable N O isotope Reference Materials (RMs).

Redefinition of the Mole in the Revised International System of Units and the Ongoing Importance of Metrology for Accurate Chemical Measurements.

This Feature highlights the role of metrology, the science of measurement, in maintaining the infrastructure we all rely on for accurate chemical measurements. In particular, the recent change to the definition of the mole, the unit of chemistry, is explained.

Breakthrough in Negating the Impact of Adsorption in Gas Reference Materials.

We have shown that an exchange dilution preparation method reduces the impact of surface adsorption of the target component in high-pressure gas mixtures used for underpinning measurements of amount-of-substance fraction. Gas mixtures are diluted in the same cylinder by releasing an aliquot of the parent mixture. Additional matrix gas is then added to the cylinder.

Stability of gaseous volatile organic compounds contained in gas cylinders with different internal wall treatments.

Measurements of volatile organic compounds (VOCs) have been ongoing for decades to track growth rates and assist in curbing emissions of these compounds into the atmosphere. To accurately establish mole fraction trends and assess the role of these gas-phase compounds in atmospheric chemistry it is essential to have good calibration standards. A necessity and precursor to accurate VOC gas standards are the gas cylinders and the internal wall treatments that aid in maintaining the stability of the mixtures over long periods of time, measured in years.

Synthetic Zero Air Reference Material for High Accuracy Greenhouse Gas Measurements.

The purity analysis of zero air is a significant contributor to the uncertainty in preparing reference materials of high impact greenhouse gases, limiting progress toward coherent and comparable measurements required to assess climate trends. We have produced a commutable synthetic zero air reference material with an oxygen, nitrogen, and argon matrix closely matching atmospheric composition. This is the critical step in preventing systematic biases from pressure broadening effects when using these reference materials to calibrate instruments based on optical spectroscopy.

Influence of Pressure on the Composition of Gaseous Reference Materials.

We have shown that the amount fraction of carbon dioxide in a nitrogen or synthetic air matrix stored in cylinders increases as the pressure of the gas mixture reduces, while the amount fraction of methane remains unchanged. Our measurements show the initial amount fraction of carbon dioxide to be lower than the gravimetric value after preparation, which we attribute to the adsorption of a proportion of the molecules to active sites on the internal surface of the cylinder and the valve. As the mixture is consumed, the pressure in the cylinder reduces and the amount fraction of the component is observed to increase.

Preparation and validation of fully synthetic standard gas mixtures with atmospheric isotopic composition for global CO2 and CH4 monitoring.

We report the preparation and validation of the first fully synthetic gaseous reference standards of CO2 and CH4 in a whole air matrix with an isotopic distribution matching that is in the ambient atmosphere. The mixtures are accurately representative of the ambient atmosphere and were prepared gravimetrically. The isotopic distribution of the CO2 was matched to the abundance in the ambient atmosphere by blending (12)C-enriched CO2 with (13)C-enriched CO2 in order to avoid measurement biases introduced by measurement instrumentation detecting only certain isotopologues.

Gaseous reference standards of formaldehyde from trioxane.

We have developed a dynamic reference standard of gaseous formaldehyde based on diffusion of the sublimate of trioxane and thermal conversion to formaldehyde in the gas phase. We have also produced a gravimetric standard for formaldehyde in a nitrogen matrix, also by thermal conversion of the sublimate of trioxane. Analysis of the gravimetric standard with respect to the dynamic standard has confirmed the comparability of the static and dynamic gravimetric values.

Sensitivities of key parameters in the preparation of silver/silver chloride electrodes used in Harned cell measurements of pH.

A questionnaire was completed by fourteen world leading national metrology institutes to study the influence of several variables in the preparation of Ag/AgCl electrodes on the accuracy of Harned cell measurements of pH. The performance of each institute in the last decade has been assessed based on their results in eight key comparisons, organized by the Bureau International des Poids et Measures Consultative Committee for Amount of Substance, involving the measurement of pH of phosphate, phthalate, carbonate, borate and tetroxalate buffer solutions. The performance of each laboratory has been correlated to the results of the questionnaire to determine the critical parameters in the preparation of Ag/AgCl electrodes and their sensitivities with respect to the accuracy of pH measurement.

Effect of silver annealing conditions on the performance of electrolytic silver/silver chloride electrodes used in Harned cell measurements of pH.

We have studied the long and short term stability of electrolytic Ag/AgCl electrodes fabricated from Ag wire that has been subjected to a range of different annealing conditions. At elevated temperatures, the presence of oxygen during the annealing process has been shown to be detrimental to the performance of electrodes produced. This phenomenon has been attributed to the dissolution of oxygen in the Ag lattice leading to structural changes in the Ag/AgCl electrode material.

Sensitivities of a standard test method for the determination of the pHe of bioethanol and suggestions for improvement.

An assessment of the sensitivities of the critical parameters in the ASTM D6423 documentary standard method for the measurement of pHe in (bio)ethanol has been undertaken. Repeatability of measurements made using the same glass electrode and reproducibility between different glass electrodes have been identified as the main contributors to the uncertainty of the values produced. Strategies to reduce the uncertainty of the measurement have been identified and tested.

Effect of Structural Design of Silver/Silver Chloride Electrodes on Stability and Response Time and the Implications for Improved Accuracy in pH Measurement.

The response time of thermal electrolytic Ag/AgCl reference electrodes is defined by the porous structure that limits the rate at which traces of any previous solution are diluted by any new solution environment. The electrode stabilisation time when transferred from one electrolyte to another has been shown to change when different structural designs to the conventional sphere of Ag/AgCl are used. Electrodes fabricated with cylindrical architectures of Ag/AgCl have shown improved stability and reach equilibrium faster than spherical electrodes.

Quantitative molecular depth profiling of organic delta-layers by C60 ion sputtering and SIMS.

Alternating layers of two different organic materials, Irganox1010 and Irganox3114, have been created using vapor deposition. The layers of Irganox3114 were very thin ( approximately 2.5 nm) in comparison to the layers of Irganox1010 ( approximately 55 or approximately 90 nm) to create an organic equivalent of the inorganic 'delta-layers' commonly employed as reference materials in dynamic secondary ion mass spectrometry.