A compact Raman laser gas spectrometer is developed. It comprises a high-power green laser at 532.123 nm as an excitation source and a specially designed gas cell with an internal volume of less than 0.6 cm³ that can withstand gas pressures up to 100 atm. The resolution of the spectrometer is ~1 cm⁻¹. The Raman spectra of chemically pure isotopically enriched carbon dioxide (¹²CO₂, ¹³CO₂) and methane (¹²CH₄, ¹³CH₄) gases are studied. The expected limit of detection (LOD) is less than 100 ppm for the isotopologues of CO₂ and less than 25 ppm for those of CH₄ (at a gas pressure of 50 atm.), making the developed spectrometer promising for studying the sources of emissions of greenhouse gases by resolving their isotopologue composition. We also show the suitability of the spectrometer for Raman spectroscopy of human exhalation.

The CCQM-K90 comparison is designed to evaluate the level of comparability of national metrology institutes (NMI) or designated institutes (DI) measurement capabilities for formaldehyde in nitrogen at a nominal mole fraction of 2 μmol mol ⁻¹ . The comparison was organised by the BIPM using a suite of gas mixtures prepared by a producer of specialty calibration gases. The BIPM assigned the formaldehyde mole fraction in the mixtures by comparison with primary mixtures generated dynamically by permeation coupled with continuous weighing in a magnetic suspension balance. The BIPM developed two dynamic sources of formaldehyde in nitrogen that provide two independent values of the formaldehyde mole fraction: the first one based on diffusion of trioxane followed by thermal conversion to formaldehyde, the second one based on permeation of formaldehyde from paraformaldehyde contained in a permeation tube. Two independent analytical methods, based on cavity ring down spectroscopy (CRDS) and Fourier transform infrared spectroscopy (FTIR) were used for the assignment procedure. Each participating institute was provided with one transfer standard and value assigned the formaldehyde mole fraction in the standard based on its own measurement capabilities. The stability of the formaldehyde mole fraction in transfer standards was deduced from repeated measurements performed at the BIPM before and after measurements performed at participating institutes. In addition, 5 control standards were kept at the BIPM for regular measurements during the course of the comparison. Temporal trends that approximately describe the linear decrease of the amount-of-substance fraction of formaldehyde in nitrogen in the transfer standards over time were estimated by two different mathematical treatments, the outcomes of which were proposed to participants. The two treatments also differed in the way measurement uncertainties arising from measurements performed at the BIPM were propagated to the uncertainty of the trend parameters, as well as how the dispersion of the dates when measurements were made by the participants was taken into account. Upon decision of the participants, the Key Comparison Reference Values were assigned by the BIPM using the largest uncertainty for measurements performed at the BIPM, linear regression without weight to calculate the trend parameters, and not taking into account the dispersion of dates for measurements made by the participant. Each transfer standard was assigned its own reference value and associated expanded uncertainty. An expression for the degree of equivalence between each participating institute and the KCRV was calculated from the comparison results and measurement uncertainties submitted by participating laboratories. Results of the alternative mathematical treatment are presented in annex of this report. Main text To reach the main text of this paper, click on Final Report . Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/ . The final report has been peer-reviewed and approved for publication by the CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Main text: The CCQM Isotope Ratio Working Group (IRWG) determined that an additional key comparison of carbon isotope delta measurements was required to capture the progress of this field. Vials containing 0.25 mg of vanillin were prepared at NRC, and evaluated for bottle-to-bottle homogeneity prior to distribution to the eight participating institutes. Participants were able to choose any suitable method and reference materials for carbon isotope delta measurements, and report a carbon isotope delta value and the associated uncertainty, and analysis details. To determine the key comparison reference value (KCRV) and its associated uncertainty, the NRC in collaboration with the NIST, developed a multivariate Bayesian random laboratory effects model, which also incorporates the uncertainty due to bottle-to-bottle homogeneity and any correlations between the reported results that arise due to the use of common reference materials. The KCRV for this study was determined to be -25.833 ‰ relative to the VPDB, with associated uncertainty of 0.028 ‰, and expanded uncertainty of 0.056 ‰ (k=2). All the results reported by the participants in this study were considered equivalent to the KCRV. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database https://www.bipm.org/kcdb/. The final report has been peer-reviewed and approved for publication by the CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

The characteristics of an optimized sampling system for measurements of isotope ratios in pure CO ₂ gas with Isotope Ratio Infrared Spectroscopy measurement systems that has achieved reproducible measurement of δ ¹³ C and δ ¹⁸ O values with 0.02‰ reproducibility (1 σ) is described. The key elements of the sampling system revolve around almost identical treatment of sample and reference gases allowing two-point calibration of up to 14 samples, and appropriate flushing protocols to remove any biases from memory effects of previously sampled gases. Measurements are performed by the Isotope Ratio Infrared Spectroscopy system at a mole fraction of nominally 700 μmol mol ⁻¹ CO ₂ in air, by dilution of pure CO ₂ gas controlled by individual low-flow mass flow controllers (0.07 ml min ⁻¹ ), and with a feedback loop to control mole fractions to ensure that differences between references and sample gas mole fraction stay below 2 μmol mol ⁻¹ . This level of control is necessary to prevent biases in measured isotope ratios, the magnitude of which has also been studied with a sensitivity study. The system has been validated using pure CO ₂ samples which range in δ ¹³ C delta values of −1‰ and −45‰ vs VPDB-CO ₂ , and in all cases measurement reproducibility over several days of testing of 0.02‰ or better (1 σ) was achieved for both δ ¹³ C and δ ¹⁸ O, with negligible memory effects. The amount of sample gas used for each measurement was less than 5 ml of CO ₂ at (RTP), making the system easily deployable for isotope ratio value assignment of bulk CO ₂ gas, and adaptable to atmospheric mole fractions of CO ₂ in air, and for value assignments of standards. Using the sampling system described the measurement reproducibility of current Isotope Ratio Infrared Spectroscopy systems approaches measurement reproducibility that can be achieved with some IRMS systems.

A Raman gas analyzer for detecting carbon isotopologues with an excitation laser with a power of 5 W, generating at a wavelength of 532 nm, focusable in a waist of 7 μm using a lens with compensation for spherical aberration is presented. The signal is detected by a high-resolution spectrometer with a matrix cooled to -40° C. The program optimization of the system parameters is presented: focusing lens, cuvette windows.