Displays

Variations in stable hydrogen (δ²H) and oxygen (δ¹⁸O) isotope ratios have been used in wildlife and forensic applications to infer the provenance of biological tissues by comparing isotopic measurements for unknown samples to geographically indexed measurements or predictions. Tissues composed of the structural protein keratin have been targeted in many systems, leading to a legacy of published data for known-origin samples. An open synthesis of these data would be useful to support broader analysis of keratin isotope patterns across biological systems and as a reference data collection for future studies.

Significant differences in sample preparation and analysis protocols and calibration and normalization approaches among laboratories have created substantial challenges in the integration of these data, however. Here we identify and assess factors that might be limiting comparability of δ²H and δ¹⁸O data among laboratories. These include sample type and sampling method, procedure for lipid extraction, whether and how partial exchange of keratin H with atmospheric moisture has been addressed, which laboratory reference materials have been used, drying and handling protocols, analysis method, and quality of chromatography for O isotopic analyses. We compile a list of reference materials (including Utah, USGS, and Saskatoon standards) and their established values, and develop a set of ‘rules’ and corrections to account for differences in processing methods and standards as well as the associated uncertainty. We apply these corrections to more than 2500 known-origin data from the literature and demonstrate that the comparability of isotopic data among laboratories is greatly improved by linking all measurements to the same scales. We highlight both the potential of the harmonized dataset for use in wildlife and forensic research as well as substantial challenges and limitations that remain.

How to cite: Magozzi, S., Contina, A., Wunder, M., Vander Zanden, H., and Bowen, G.: A global compilation of known-origin keratin hydrogen and oxygen isotope data for wildlife and forensic research, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9674, https://doi.org/10.5194/egusphere-egu2020-9674, 2020.

Stable isotope measurements of nonexchangeable hydrogen (δ²H_n) of bulk organic matter has emerged as a tool, with a wide range of applications in biology, biogeochemistry and forensics. However, reproducible and precise measurements of δ²H_n between laboratories and methods are still challenging. One of the largest impediments to obtain accurate isotope ratios is to use reference materials of similar exchangeable hydrogen fraction (f_x) to the matrix of interest. The organic matter has typically three pools of hydrogen (H): (i) the adsorbed water, which can be minimized by extensive drying, (ii) the carbon bound H (the fraction of interest), which is non-exchangeable and cannot be removed and (iii) the non-carbon bound H, (i.e. N-, COO-, O-, and S-bound H) that cannot be removed but can be readily exchanged with the environmental moisture. Quantification of f_x based on dual water vapor isotope exchange and Isotope Ratio Mass Spectrometry (IRMS) have shown large variability in f_x between studies for the same organic matter type such as keratin. High variability in f_x between samples and standards can translate into a large impact on the measured isotopic values. Here we used a novel approach to independently quantify f_x in 21 natural organic material sources with minimal sample manipulation based on ¹H-²H exchange experiments and quantified through proton based liquid-state nuclear magnetic resonance (¹H-NMR) spectroscopy. The experiments were carried out at room temperature by immersing separate solid powdered samples in deuterated dimethylsulfoxide (background) and deuterium oxide (²H source) followed by the quantification of the water generated in the supernatant fraction through ¹H-NMR using glucose as reference. At the same time, samples were analyzed through the most recent procedure of dual water vapor isotope equilibration method using online drying and equilibration in a UniPrep carousel. We discuss these findings and suggest that the proposed ¹H-NMR method of quantifying f_x is an independent and novel approach that can contribute to a better understanding of H exchangeability in a wider range of organic materials, critical for accurate measurement of the δ²H_n.

How to cite: Gudasz, C., Soto, D. X., Sparrman, T., and Karlsson, J.: A novel method to quantify exchangeable hydrogen fraction in organic matter, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11630, https://doi.org/10.5194/egusphere-egu2020-11630, 2020.

Minerals of the apatite group, especially hydroxylapatite Ca₅(PO₄)₃OH, are valuable archives for reconstructing environmental conditions occurring throughout the Earth’s history (e.g., Joachimski et al. 2009). Apatite oxygen isotope compositions have proved useful in studies of conodonts as well as fish and mammalian teeth and bones. Secondary ion mass spectrometry (SIMS) is a rapid and precise technique that enables the investigation of small and heterogeneous samples. However, this method is constrained by the availability of matrix-matched reference materials (RMs). The most commonly used RM for calibrating δ¹⁸O phosphate SIMS measurements – Durango apatite – has been found to be heterogeneous (Sun et al. 2016); therefore, we have undertaken this study, in which we have characterized a new suite of RMs for oxygen isotope analyses of apatite. Four potential apatite RMs obtained from various sources were assessed for ¹⁸O/¹⁶O homogeneity using SIMS. The major and trace element compositions were determined by electron probe microanalyses (FE-EPMA), while the contents of OH^- and CO₃^2- were assessed using thermogravimetric analysis (TG) and infrared spectroscopy (IR). The δ¹⁸O reference values have now been determined in six independent laboratories using isotope ratio mass spectrometry (IRMS) and applying different analytical protocols, which fall into two groups: laser fluorination and high-temperature reduction of Ag₃PO₄. The first method provides the information on “bulk” oxygen compositions, while the second determines the composition of phosphate-bound oxygen. The repeatability of SIMS measurements on random crystal fragments was better than 0.25‰ (1 standard deviation, 1s) for the different RMs, confirming good homogeneity at the nanogram scale. The IRMS-determined δ¹⁸O_SMOW values, which fall between ~5 and ~22‰ for the different samples, cover almost the full range of compositions found in igneous, metamorphic and biogenic apatite samples. However, the IRMS data collected using different techniques show offsets of ~1-2‰. The δ¹⁸O values obtained using laser fluorination are, in most cases, lower than those acquired by high-temperature reduction. Furthermore, the data collected within each group of IRMS methods reveal differences between laboratories, which do not correlate with the chemical composition of the apatite crystals. This suggests a more complex behavior of apatite during sample processing for conventional δ¹⁸O analyses as compared to other minerals such as tourmaline, and highlights the importance of the characterization of RMs with the support of multiple laboratories applying different protocols.

This research was partially funded by the Polish NCN grant no. 2013/11/B/ST10/04753 and the IGS PAS grant for the early career researchers as well as supported by the COST Action TD 1308 “ORIGINS” and the German Academic Exchange Service (DAAD).

References

Joachimski et al. 2009. Earth and Planetary Science Letters, 284, 599-609. doi: 10.1016/j.epsl.2009.05.028

Sun et al. 2016. Chemical Geology, 440, 164-178. doi: 10.1016/j.chemgeo.2016.07.013

How to cite: Wudarska, A., Wiedenbeck, M., Słaby, E., Harris, C., Joachimski, M. M., Lécuyer, C., MacLeod, K. G., Pack, A., Vennemann, T., Couffignal, F., Glodny, J., Kusebauch, C., Lempart, M., Sun, Y., and Wilke, F.: SIMS- and IRMS-based study of apatite reference materials reveals new analytical challenges for oxygen isotope analysis, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18841, https://doi.org/10.5194/egusphere-egu2020-18841, 2020.

An international project developed, quality-tested, and measured isotope−delta values of 10 new food matrix reference materials (RMs) for hydrogen, carbon, nitrogen, oxygen, and sulfur stable isotope-ratio measurements to support food authenticity testing and food provenance verification. These new RMs will enable users to normalize measurements of samples to isotope−delta scales. The RMs span a range of δ²H_VSMOW values from −207.4 to −43.3 mUr or ‰, for δ¹³C_VPDB from −30.60 to −13.72 mUr, for δ¹⁵N_air from +1.78 to +14.96 mUr, for δ¹⁸O_VSMOW from +18.20 to +26.33 mUr, and for δ³⁴S_VCDT from −20.25 to +17.49 mUr. The RMs include (i) a pair of honeys from Canada and tropical Vietnam, (ii) flours from C3 (rice) and C4 (millet) plants, (iii) four vegetable oils from C3 (olive, peanut) and C4 (corn) plants, and (iv) collagen powders from marine fish and terrestrial mammal origins. After thorough homogenization of the bulk materials, multiple aliquots were sealed in glass under vacuum or noble gas to exclude oxygen and to potentially extend the shelf life to decades when stored at –18 °C in the dark. A total of six laboratories from five countries used various analytical approaches and instrumentation for two- or multiple-point isotopic normalization against international RMs. The use of reference waters and organic liquids in silver tubes allowed direct normalization of δ²H values of organic materials against isotopic reference waters following the principle of identical treatment, minimizing interference from atmospheric moisture. An errors-in-variables regression model that included the uncertainty associated with the measured and assigned values of the RMs was applied centrally to normalize results and obtain consensus values and measurement uncertainties reported here for new RMs USGS82 to USGS91. Because of exchangeable hydrogen and H₂O in some RMs (especially in honeys, collagens, and flours), sample loading in contact with laboratory air and different types of pre-treatment can result in significant bulk δ²H variance. Utilization of these new RMs should foster mutual compatibility of δ²H values if harmonized technical/analytical approaches are followed and documented in data reports.

How to cite: Ogrinc, N., Schimmelmann, A., Qi, H., Camin, F., Bontempo, L., Potočnik, D., Abrahim, A., Cannavan, A., Carter, J. F., Dunn, P. J. H., Reid, L. T., and Coplen, T. B.: Upcoming food matrix stable isotope reference materials from the USGS: honeys, vegetable oils, flours, and collagens, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22332, https://doi.org/10.5194/egusphere-egu2020-22332, 2020.

Throughout the past decades, δ¹⁸O and δ²H of the water molecule have been widely used as tracers in the hydrological and climatological sciences. Until the late 2000s, isotope-ratio mass spectrometry was the only available analytical technology, with associated capital investments, operating expenditures and human resource and infrastructure requirements. The advent of laser spectrometric techniques during the last decade has reduced most of these requirements and enabled a great number of research groups to conduct their own analyses rather than contracting these out. This is a crucial advance especially for countries where resources to operate mass spectrometry laboratories are limited and has resulted in a boost of the usage of δ¹⁸O and δ²H in research and applied water management. However, the rapid proliferation of laser spectrometers has raised occasional QA/QC concerns about the data resulting from such laboratories, which is not only to the detriment of the research groups concerned, but also to the science and analytical technology as such.

To address these concerns, we organized a geographically constrained laboratory intercomparison exercise involving 25 laboratories with δ¹⁸O and δ²H analytical capabilities in the Latin American and Caribbean (LAC) region. The exercise was preceded by a survey questionnaire which provided information on the instrumentation, reference materials, data processing techniques and QA/QC approaches, as well as a self-assessment of the available human resources for δ¹⁸O and δ²H analysis. Consecutively, three test samples were provided to the laboratories, and results collected in a template form. We used z-scores to assess performance per sample and aggregated to laboratory level, with a fairly tight standard deviation of the proficiency test of 0.1 ‰ for δ¹⁸O and 0.8 ‰ for δ²H, which we deemed fit for purpose in hydrological investigations. Laboratory performance was ranked as satisfactory if z<2, questionable if 2≤z<3 and unsatisfactory if z≥3. After the deadline, all laboratories received an individual performance report.

Our results show that: (i) that 90% of the submissions were measured by laser spectrometry; (ii) for δ²H, 80% of the laboratories submitted satisfactory results (10% questionable) and (iii) for δ¹⁸O the results were more variable resulting in 50% satisfactory and 35% questionable submissions. We therefore conclude that most laboratories in the region can provide δ²H results that are fit for purpose, however with quite some margin for improvement in δ¹⁸O. This may be explainable in part by the technical challenges of δ¹⁸O assays on laser spectrometers compared to δ²H (e.g. dependency of δ¹⁸O on the H₂O concentration). We attempted to identify key factors of good and poor performance; however, on the fairly small number of participants, no obvious causes could be identified. There are indications that commonly known questionable practices may negatively influence performance, with the reasons for that (lack of resources or access thereto, inadequate training or awareness) to be determined.

How to cite: Terzer-Wassmuth, S., Ortega, L., Araguas-Araguas, L., and Wassenaar, L. I.: LAC-IC 2018: Evaluation of the first IAEA regional water δ¹⁸O/δ²H interlaboratory comparison exercise, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22653, https://doi.org/10.5194/egusphere-egu2020-22653, 2020.

Nowadays stable isotope data need to be accompanied by meaningful uncertainty statements for their full utilisation, whether to evaluate their isotopic composition as evidence for origin of samples, for observation and proper evaluation of small isotopic trends due to transient effects, or to their use as laboratory standards. The Guide of Expression of Uncertainty in Measurements (GUM) provides a general framework to perform the task to calculate data with combined standard uncertainties. However, combining several such measurement data in a proper way is not straightforward without consideration of the correlation matrix and mathematical complicated elaborations. An Excel based tool provides means for any laboratory to calculate individual data with their associated combined standard uncertainties, including all major sources of uncertainty like the repeatability and long-term reproducibility of measurements, the possible bias of quality controls, the assigned uncertainty of used reference materials and their measurement data scatter. The tool further allows to calculate and correct memory effects and drifts as occurring in measurements. Standardised correction means allow the merging of data from different instruments with varying performance. This provides ultimately the means to combine such data without compromising the validity of the calculated combined standard uncertainty of the average value. This constitutes the possibility to produce a meaningful reference value with associated combined standard uncertainty from heterogeneous data, e.g. for the purpose to characterize a laboratory reference material by use of independent methods. The tool (SICalib) is available free of charge, is based on Excel macros as a standalone tool for measured rawdata files without the requirement of any particular database or other tool, and is still under further development. Its intention is complementary to available data management systems with a focus of proper uncertainty propagation.

How to cite: Groening, M.: Consistent data compilation and error propagation for stable isotope data to compile meaningful reference values and uncertainties , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22506, https://doi.org/10.5194/egusphere-egu2020-22506, 2020.

Isotope ratios offer countless applications but almost as a rule precision measurements are required. Making use of such measurements involves comparison of the results between the laboratories which, in turn, requires international primary standards. Much less appreciated is the role of data analysis and measurement models. This presentation will feature a variety of examples of stable isotope ratio measurements, including light and heavy elements with examples from the redefinition of the kilogram, lead-lead dating, and carbon isotope delta reference scales, showing that choices on how we interpret and model our measurements can affect the traceability and comparability of isotope ratio measurements. The challenge is therefore for the analysts to recognize data analysis practices as a natural part of the measurement.

How to cite: Meija, J.: Traceability in isotope ratio measurements: the role of data analysis, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22382, https://doi.org/10.5194/egusphere-egu2020-22382, 2020.

The second largest city in Romania (Cluj-Napoca) is supplied with drinking water originating from the upper basin of Somesul Mic river (SMR). As part of an ongoing project, we aim to investigate the origin, flow and quality of water consumed in the city by collecting monthly river, lake, tap and groundwater and performing physical, chemical and stable isotope analyses (d18O and d2H in water, and d13C in DIC). However, owing to the different types of water bodies to be sampled and the local climate, with freezing conditions for up to six months in the upper basin, the results of the analyses might indicate time and space specific conditions, rather than the general hydrologic conditions we were targeting. Thus, we have modified our approach, and have devised a secondary sampling strategy in order to address these issues.

We present here a sampling strategy that aims to disentangle between different factors controlling the stable isotope composition of surface waters under different geomorphologic and climatic conditions and minimize the risk of introducing unwanted biases. Briefly, we have sampled water under both freezing and non-freezing conditions from the rivers and lakes along the main trunk of SMR and measured d18O (and d2H) in water, as well as d13C in DIC. Our data shows that the presence of ice strongly affects that stable isotope composition of river and lake water (as a result of strong kinetic processes resulting from the specifics of water solidification) and the results of these measurements are meaningless when trying to understand the connections between the various water bodies. Contrary, d13C in DIC was less affected by the freezing processes, a finding mirrored by the chemical values of the water. However, the later were strongly influenced by local geomorphologic conditions, both in summer and winter. In lakes, sampling at different locations on the surface and at different depths resulted in a wide range of stable isotope ratios for O and H, unrelated to values measured in the inflowing and outflowing streams. Overall, our data suggest that monthly stable isotope values of river and lake water along a flow path are difficult to interpret in terms of residence and transit times and mixing of sources. Thus, in regions where freezing is recurrent, kinetic fractionation processes have a contribution to the “final” stable isotope composition of water that is higher than that resulting from other (hydrological) processes. Contrary, more valuable data was obtained when the stable isotope composition of surface waters was compared with that of precipitation water, allowing for possible identification of moisture sources and pathways feeding the local water bodies. We conclude that in order to generate valuable data, quality control must first start with designing site-specific protocols for sampling and stable isotope analyses of water and factors altering the “sought-for” values should be considered first before interpreting the results.

The IAEA partly supported this study through contract numbers 23870 and 23550. The research leading to these results has received funding from the EEA Grants 2014-2021, under Project contract 4/2019 (GROUNDWATERISK).

How to cite: Brad, T., Persoiu, A., and Ionescu, A.: Pitfalls, questions and solutions when sampling water for stable isotope analyses along complex riverine systems, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20490, https://doi.org/10.5194/egusphere-egu2020-20490, 2020.

We have developed an analytical method for the precise δ¹³C measurement of individual amino acid using a multi-dimensional high-performance liquid chromatography (HPLC) and a nano-scale elemental analyzer/isotope ratio mass spectrometry (EA/IRMS). Although this method is time-consuming, it can offer higher precision and accuracy than does the conventional analytical method such as GC/C/IRMS, because the derivatization of amino acids is not required. A reversed-phase column (CAPCELL PAK C18, Shiseido, Japan) and a mixed-mode column (Primesep A, SIELC Technologies, U.S.A.) were applied for the HPLC (Agilent Technologies, U.S.A.) with a charged aerosol detector (Thermo Fisher Scientific, U.S.A.) (Ishikawa et al., 2018). We conducted the isolation of underivatized amino acids in a standard mixture containing 15 proteinogenic amino acids (Gly, Ala, Glu, Arg, Val, Pro, Met, Tyr, Ile, Leu, Phe, Thr, His, Asp, Ser), and confirmed that all these amino acids were successfully isolated. Each collected amino acid was filtered through a 0.45 μm membrane filter (Pall, U.S.A.) and washed with diethyl ether to remove hydrophobic impurities. The δ¹³C values of these amino acids before and after the separation and purification were consistent, which proved that the whole experimental procedure did not change the δ¹³C values of amino acids. We applied this method to several aquatic organisms. The results show that the δ¹³C values of amino acids vary as large as 30‰ with Gly being most enriched in ¹³C.

Reference

Ishikawa et al., (2018) Anal. Chem., 90, 20, 12035-12041.

How to cite: Sun, Y., Ishikawa, N. F., Ogawa, N. O., Kawahata, H., Takano, Y., and Ohkouchi, N.: High-precision compound-specific carbon isotopic analysis of underivatized amino acids using a multi-dimensional-HPLC and nano-EA/IRMS, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1601, https://doi.org/10.5194/egusphere-egu2020-1601, 2020.

Fossil bioapatite is widely used as a proxy to estimate paleoclimatic and/or – environmental conditions. However, the scarcity of well–preserved specimens in some samples mingled with their small sizes frequently compromise the application of notable geochemical techniques (e. g., laser fluorination). While some in–situ and non–destructive methods allow studies of single specimens, it is important to understand the specimens’ microstructure and the elemental– and isotopic variations between structurally different parts. These parameters may vary as a function of the environmental conditions during the formation of biogenic tissue. To better understand the nature of bioapatites, different geochemical techniques were applied to apparently well–preserved samples of distinct age: conodonts (Early Triassic, CAI 1 to 2), fossil (Paleogene) and modern shark teeth. The microstructure and element distribution of the samples were investigated using scanning electron microscopy (SEM) and an electron microprobe (EMPA), respectively. Paleoenvironmental conditions and relative sea water temperatures in which bioapatites were formed is grounded in stable oxygen isotope analyses (δ¹⁸O_PO4). Two methods were used for measurements of the δ¹⁸O_PO4 values: a classical method using bulk sampling and high temperature reduction (HTR) analysis, and in–situ measurements by secondary ion mass spectrometry (SIMS). Quantitative analyses and chemical maps of segminiplanate conodont P₁–elements are often found to be heterogeneous in terms of their element concentrations. The reason for this heterogeneous element distribution may be related to conodonts retracting their teeth during growth, suggested notably by variations in Mg, S and Na concentrations. Stable oxygen isotope measurements by HTR reproduced better than ±0.3 ‰ of standard deviations for most bioapatites. Conodonts from Timor analyzed by SIMS could be separated into three distinct groups (TM_base, TM_post, TM_inner), based on differences in their δ¹⁸O_PO4 values. In the analyzed samples where the hyaline crown is mixed with the albid crown, variations in δ¹⁸O_PO4 values are larger (TM_post: 16±1 ‰, n = 13; TM_inner: 15.7±1.9 ‰, n = 11) than samples where only the hyaline crown was analyzed (TM_base: 17.1±0.2 ‰, n = 12). Moreover, the δ¹⁸O_PO4 values from the latter dataset overlap with those from Timor samples analyzed by HTR (17.3±0.4 ‰, n = 7). Shark teeth had a larger variation in their δ¹⁸O_PO4 values as well when analyzed by the in–situ technique. The inter–tissue δ¹⁸O_PO4 variation between enameloid zones in the same tooth is up to 5.5 ‰. The heterogeneity in the elemental concentrations of the studied bioapatites apparently do not result in significantly machine fractionation for the in–situ (SIMS) stable oxygen isotopic measurements. Instead, variation of δ¹⁸O_PO4 values appears to be sensitive to remains of organic matter/carbonate in phosphate, analytical artefacts related to sample topography (for sharks) or vital effects. Based on these results, the conodont sample set from Timor (Scythogondolella ex. gr. milleri) was chosen as an internal standard for stable isotope analyses in bioapatite of the SwissSIMS laboratory. This new in–house standard could be used to normalize the oxygen isotope values and consequently help interpret variations in paleoclimate and/or – environmental conditions for bioapatite.

How to cite: Luz, Z., Leu, M., Baumgartner, L. P., Bucher, H., and Vennemann, T.: New insights for studying phosphate stable oxygen isotopes in bioapatites interpreted from their geochemistry, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20624, https://doi.org/10.5194/egusphere-egu2020-20624, 2020.

Isotope ratio measurement systems based on optical spectrometers becomes widely used because of several important advantages. First is fundamental possibility to distinguish the isotopologues with the same molecular weight but different isotopic composition like ¹⁶O¹³C¹⁶O and ¹⁶O¹²C¹⁷O. Second is fundamental possibility to perform calibration free absolute measurement of different isotopologues based on ab initio calculations of line intensities [1]. Third is experimental usability, field deployability and low cost of the optical instruments.

The disadvantage of the optical isotope ratio spectrometers available on the market compared to the isotope ratio mass spectrometers is still low accuracy associated not only with the capabilities of optical instruments as such, but also with the lack of high-precision measurement procedures. To improve the accuracy of the optical measurement system, the main factors affecting the measurement result should be investigated and eliminated.

In this study, we used CM-CRDS carbon isotope ratio measurement system consisted of Picarro G2131i analyzer, Picarro combustion module, Picarro Caddy Universal interface, homemade system of solenoid valves Camozzi. The calibration of the measurement system was made by combustion of certified reference materials from the International Atomic Energy Agency as recommended in [2].  The linearity of the delta scale was evaluated. Non-linearity of the delta scale leads to a bias if just one or two certified reference materials are used for calibration.

The measurement procedure of carbon isotope ratios in solid sample on CM-CRDS is as follows. A sample is broken down into elemental components in the combustion module. After the cleaning from interfering components, CO₂ is diluted with nitrogen and analyzed by CRDS instrument. The similar procedure is performed with reference material. The issue is that even if the mass of sample and reference material are the same, the concentration of CO₂ in the analyzed mixture is different. Mismatch of concentrations leads to bias in measured isotope ratios. The magnitude of concentration dependence is estimated in this study.

The obtained results are discussed and ways to eliminate the abovementioned issues are proposed.

[1] Polyansky, Oleg & Bielska, Katarzyna & Ghysels, Mélanie & Lodi, Lorenzo & Zobov, Nikolai & Hodges, Joseph & Tennyson, Jonathan. (2015). High-Accuracy CO2 Line Intensities Determined from Theory and Experiment. Physical Review Letters. 114. 10.1103/PhysRevLett.114.243001.

[2] Willi A. Brand et al. Assessment of international reference materials for isotope-ratio analysis (IUPAC Technical Report). Pure Appl. Chem., 2014, 86(3), Pages 425–467

How to cite: Chubchenko, I. and Konopelko, L.: Concentration dependence and scale linearity of the carbon isotope ratio measurement systems based on CRDS, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17571, https://doi.org/10.5194/egusphere-egu2020-17571, 2020.

Carbon isotope ratios are typically expressed as isotope delta values d(¹³C/¹²C), often shortened to d¹³C. These are isotope ratios expressed relative to an international measurement standard, which for more than 30 years has been the virtual carbonate Vienna Peedee Belemnite (VPDB). While carbon isotope delta values relative to VPDB can be obtained with very small uncertainties, maintenance of the VPDB scale itself is challenging as it is based upon artefacts with exactly assigned isotope delta values. Linking the VPDB isotope delta scale to the SI would alleviate some of the issues inherent to artefact-based scales and aid long-term comparability of measurement results. Such a link is provided by determination of absolute isotope ratios, i.e., R(¹³C/¹²C).

New and improved methods for SI-traceable measurements of R(¹³C/¹²C) by both gas source isotope ratio mass spectrometry (IRMS) and multicollector inductively coupled plasma mass spectrometry (MC-ICPMS) have been developed at LGC. These methods are based on the calibration approach using synthetic isotopologue mixtures. The developed methodology has been successfully applied to producing glycine reference materials, ERM-AE672a and LGC171-KT, with certified SI-traceable n(¹³C)/n(¹²C) isotope amount ratios under ISO 17025 and 17034 accreditations together with indicative d(¹³C/¹²C)_VPDB values traceable to VPDB.

These new reference materials realise an absolute isotope ratio for VPDB itself R(¹³C/¹²C)_VPDB through regression of the  n(¹³C)/n(¹²C) against d(¹³C/¹²C)_VPDB values. Examining all published values for R(¹³C/¹²C)_VPDB, including our most recent results, allows a better estimation of this quantity than has previously been achievable and points the way towards linking the VPDB isotope delta scale more firmly to the SI.

How to cite: Malinovskiy, D., Dunn, P., and Goenaga-Infante, H.: Determination of n(13C)/n(12C) isotope ratios by MC-ICPMS and IRMS for providing improved R(13C/12C) value of the zero-point of the VPDB isotope delta scale, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21968, https://doi.org/10.5194/egusphere-egu2020-21968, 2020.

Stable isotopes are widely used with applications in forensics, ecology, biogeochemistry, atmospheric sciences, and hydrology. Isotope data are frequently compared and combined, which requires data of high quality. This brings to the attention how comparable the data is and the need for an internal Quality System in research and service laboratories to support data quality. Since the amount of isotope data produced in the recent years has increased considerably, a plea for high-quality isotope data is required.  Estimations of data quality including uncertainty calculations may be complicated by various and not well-controlled factors, including sample matrix effects, incomplete reactions and byproducts formed etc. The use of data scatter (e.g. Standard deviation of certified reference materials and in-house working standards) as a measure of uncertainty is obviously insufficient. Instead, one may consider other or combined data quality indexes. The use of a simplified uncertainty estimation together with z-scores calculation enhances the assessment of lab performance and quality and increases the likelihood to accept the target performance chosen by any isotope laboratory. However, uncertainties associated to unknown samples also reduces the probability of obtaining significant differences between sample groups, which the purpose of the analysis could not fit. Here we discuss the criteria to revise limits of QC materials (e.g. lab standards) in an objective manner including the removal of outliers. Warning and action limits depend on the stable isotopic composition of the material (enriched vs. natural abundance), the homogeneity of the material, and the statistical approach utilized. We will report data of 1-2 years of QC tools of a soil standard material obtained at the laboratory in UKCEH-Lancaster and we will discuss how to deal with internal QC system including outlier removal, sample preparation issues, etc. Implementation of these or similar QC protocols are of great relevance for a well-based decision making when using isotope results.

How to cite: Soto, D. X., Assonov, S., Grant, H., Pereira, M. G., and Fajgelj, A.: How good are my stable isotope data? Implications on using an in-house Quality Control system for stable isotope measurements, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9055, https://doi.org/10.5194/egusphere-egu2020-9055, 2020.

The stable isotope scales of the light elements (H, C, O, S) are artefact-based (related to a primary reference material) and their practical realisation is based on several refence materials (RMs) traceable to the primary RM on a respective delta-scale. NBS19 carbonate, the primary RM for the VPDB scale introduced in 1987, exhausted in 2012, and its replacement was not available for several years. In 2016, IAEA-603 carbonate (replacement for NBS19) was released as the new primary RM having been carefully calibrated versus the remaining NBS19. The IAEA-603 uncertainty in δ13C and δ18O for the first batch (5200 ampoules produced) is ±0.010 ‰ and ±0.040 ‰ respectively (1-sigma level); the homogeneity assessment is the major component of total uncertainty which is limited by the best mass-spectrometer performance and the method (carbonate-acid reaction) reproducibility.

In 2015, monitoring of LSVEC (formerly the second scale-anchor on the VPDB scale) detected variable drifts in its δ13C value and therefore the use of LSVEC as RM for δ13C was discontinued. It was recognised that a replacement for LSVEC is needed for normalization of the δ13C measurement results, also to address the strict uncertainty requirements for δ13C observations in atmospheric CO2 and methane (≤0.01 ‰ and ≤0.02 ‰ correspondingly). Similar to IAEA-603, any new RMs will address the technical requirements for RMs laid out by ISO Guide 35: 2017 including (i) RM batch production and batch characterisation; (ii) homogeneity and stability assessment of the final product (RMs sealed off in 0.5 g ampoules) and (iii) value and uncertainty assignment based on the metrological traceability. Three new carbonate RMs are in preparation at the IAEA; the uncertainty in δ13C for all three materials due to RM’ homogeneity is already confirmed at ≤0.01 ‰ (on 10 mg aliquots), which is at the limit of the best modern mass-spectrometers. The isotopic characterisation of these new carbonate RMs is in progress; they should be released in 2020.

Together with IAEA-603, the three new RMs will provide a reliable realization of the VPDB scale with the lowest possible uncertainty. With these RMs users can (i) select RMs in a suitable δ13C range, (ii) detect any potential drift of RMs including the behaviour of daily lab-standards and (iii) detect any potential problem in applying the 17O correction at end-user laboratories. In conclusion, these new reference materials will allow laboratories worldwide to establish metrological comparability for decades.

How to cite: Assonov, S., Fajgelj, A., and Gröning, M.: The IAEA carbonate reference materials aimed at the VPDB scale realization with low uncertainty. , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11525, https://doi.org/10.5194/egusphere-egu2020-11525, 2020.

Lead is a non-essential toxic element that at high levels of human exposure causes damage to many organs of the human body. This element naturally occurs in the Earth crust, but its biogeochemical cycle has been altered by anthropogenic activities, which have introduced high amount of this element from different sources. Among inorganic contaminants, Pb is perhaps the most studied, but the determination of its total concentration only is not sufficient for a proper evaluation of contamination sources. Discrimination of anthropogenic and geogenic lead sources requires both precise and accurate isotope ratio determination as well as high versatility due to the complexity of environmental matrices, such as sediments, biota and seawater. This element has a partially radiogenic isotopic composition with 208Pb, 206Pb and 207Pb originating from the radioactive decay of 238U, 235U and 232Th respectively and 204Pb representing the only natural stable isotope. This characteristic isotopic composition represents a powerful analytical tool as it allows to trace the sources, fate and effects of possible Pb contamination. The most common way to express the Pb isotopic composition is using the ratio 206Pb/207Pb, because of the easy interference-free determination and isotopes’ abundance. The determination of 204Pb by ICP-MS is quite challenging as this is also the least abundant among Pb isotopes (about 1.4%) and it is also affected by isobaric interference from 204Hg. The latter derives from both sample matrices and from plasma/sweep gas supplies and it represents a big analytical challenge, especially for marine biota samples, where the amount of Hg can be up to 100 times higher than Pb.

In this work we present the development and the application of analytical methodology for the accurate and precise determination of Pb isotope ratios by HR-ICP-MS in different marine environmental matrices (sediments, seawater and biota). Analytical procedures are involving a separation of Pb from the sample matrix and mercury, present in the sample. For seawater samples, the use of the SeaFAST automated system allowed simultaneous matrix separation and analyte pre-concentration before ICP-MS analysis. A comparison of results for lead isotope ratios obtained with MC-ICP-MS and HR ICP-MS in the same samples, in all cases, showed very good agreement . The total uncertainty associated to each result was estimated and all major contributions to the combined uncertainty of the obtained results were identified. As all such studies involve companions of different datasets, the uncertainty estimation is critical to ensure correct companions.  The developed methodology was applied to different marine samples, namely sediments from Caribbean, Baltic and Namibian coasts, biota samples from French Polynesia, seawater samples from Mediterranean and Arctic seas. 

How to cite: Vassileva, E., Orani, A. M., and Assonov, S.: Application of lead isotope ratios for pollution source investigation in the marine environment, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22611, https://doi.org/10.5194/egusphere-egu2020-22611, 2020.

Here, we introduce a new methodology developed for highly precise stable mercury isotope ratio (δHg) analysis: the sampling method collecting sufficient amount of gaseous elemental mercury (GEM) from air within 24 h or less and the extraction method effectively converting the collected GEM to Hg²⁺ in less than 10 mL of acidified solution.

A big gold-amalgam trap (BAuT), which has approximately 11 times larger inner diameter of the tube and more gold-amalgam granular than a conventional gold-amalgam trap, was designed for quick and effective sampling of GEM in a short time period. A 24-h sampling demonstrated that the collection efficiency was higher than 99.9% under the flow rate of 55 LPM. Prior to the extraction the collected GEM by BAuT was pre-concentrated to a conventional gold-amalgam trap to reduce the dead volume.

The GEM pre-concentrated was transferred into a four side sealed 2L Tedler bag with a PTFE stopcock by heating the gold-amalgam trap to 600 ºC for ~ 4 min under the 0.5 LPM flow of Hg-free air. Prior to this transfer 5mL of 0.5~40% (v/v) reversed aqua resia or RAR (hydrochloric acid: nitric acid = 1:2) was pre-introduced into the bag. The bag with GEM and RAR was left for the conversion of GEM into the stable state in the solution (i.e., Hg²⁺). The solution recovered was then analyzed by multi collector-ICP-MS for the Hg concentration and δHg.

Results with a standard reference material showed that the recovery from the test with 10% RAR and the extraction duration of 8 days was the highest, 97%, with the 5% of recovery for the residual GEM in the gas-phase. The δHg analysis for five isotope ratios exhibited that the accuracy was between 0.01 and 0.3 ‰. Results from the analytical tests of ambient GEM using this methodology will be discussed.

How to cite: Irei, S.: A novel method for stable isotope measurement of gaseous elemental mercury, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22474, https://doi.org/10.5194/egusphere-egu2020-22474, 2020.

Stable nickel isotopes are known to fractionate by biological processes and their measurements can be important biomarker. In searches for ancient fossilised materials such as microbial cells, the Ni isotope fractionation record can be preserved after death and fossilization of microstructures. Typically, transition metal isotopes in microfossils are difficult to measure accurately because of their low concentration in the fossil. Furthermore, microsized fossil structures  are difficult to isolate from the host phase. Thus, the measurement of their chemical composition can be conducted only by a few  analytical methods. We have applied femtosecond-laser ablation/ionisation time-of-flight mass spectrometry (LIMS) to measure chemical composition of the fossilised material embedded in the aragonite phase and accurately derive the Ni isotopic fractionation pattern. High resolution depth profiling method was applied to isolate fossilised material composition from the host phase. The mass peak intensity correlation and peak integration methods were subsequently applied to derive isotope concentrations. The accuracies and precision in permill level or better of the isotope values were achieved. For comparison the studies of Ni isotopes were conducted on inorganic samples. The instrument used in the studies is a miniature mass analyser developed for space research holding promisses that differentiation between abiotic and biogenic microstructures in rocks can be studied also in situ on the surfaces of Solar System bodies.

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How to cite: Tulej, M., Neubeck, A., Lukmanov, R., Grimaudo, V., Riedo, A., Cedeño López, A., de Koning, C. P., Ligterink, N. F. W., Ivarsson, M., and Wurz, P.: Determination of the Ni isotope fractionation in microfossils embedded in the aragonite phase, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4248, https://doi.org/10.5194/egusphere-egu2020-4248, 2020.

Like many other elements, iridium is lacking a calibrated, SI traceable isotope ratio measurement. In this study, we
have undertaken absolute isotope amount ratio measurements of iridium by multicollector inductively coupled plasma mass
spectrometry (MC-ICPMS) using a state-of-the-art regression model to correct for the instrumental fractionation (mass bias) of
isotope ratios using both NIST SRM 997 isotopic thallium and NIST SRM 989 isotopic rhenium as primary calibrators. The
optimized regression mass bias correction model is based on incrementally increasing plasma power and short (10−30 min)
measurement sessions. This experimental design allows fast implementation of the regression method which would normally
require hours-long measurement sessions when executed under constant plasma power. Measurements of four commercial
iridium materials provide a calibrated iridium isotope ratio R193/191 = 1.6866(6)k=1 which corresponds to isotopic abundance x191
= 0.372 21(8)k=1 and an atomic weight of Ar(Ir) = 192.217 63(17)k=1. In addition, we present data on a new Certified Reference
Material from NRC Canada IRIS-1 which fulfills the requirements of a delta zero reference for iridium isotope ratio
measurements.

How to cite: Zhu, Z.: Determination of the Isotopic Composition of Iridium Using Multicollector-ICPMS, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21941, https://doi.org/10.5194/egusphere-egu2020-21941, 2020.