Conference Agenda

Understanding the impact of human activities on the metabolic state of organisms from soil and aquatic environments is of paramount importance to implement measures for maintaining ecosystem services. Variations of natural abundance ¹⁸O/¹⁶O ratios in phosphate have been proposed as proxies for the assessment of variations in metabolic activity given the crucial importance of phosphoryl transfer reactions (i.e., the nucleophilic displacement of PO₃^2- groups between phosphate esters and water) in biological processes. However, limitations inherent to oxygen isotope analysis by isotope-ratio mass spectrometers have so far restricted a stable isotope-based evaluation of these metabolic processes.

To that end, we explore novel opportunities for oxygen isotope analysis of phosphate and organophosphorus compounds by electrospray ionization (ESI) Orbitrap mass spectrometry (MS) in three steps. First, we identified and optimised critical instrument parameters for accurate ¹⁸O/¹⁶O ratio analysis from the isotopologues of H₂PO₄^-. Second, we established the accuracy of ¹⁸O/¹⁶O ratio analysis after phosphate fragmentation to PO₃^- to enable oxygen isotope ratio measurements of organophosphorus compounds. Finally, we evaluate the selective phosphate extraction and analyte purification using Zr-based metal organic frameworks (MOFs).

Our results demonstrate that ¹⁸O/¹⁶O ratios of phosphate and organophosphorus compounds can be determined accurately from both H₂PO₄^- and PO₃^- ions over the range of environmentally observed ¹⁸O/¹⁶O ratios. Measurements are reproducible over more than one year of repeated analyses on a standard ESI-Orbitrap-MS device at phosphate concentrations of 50 µM. Our data furthermore show that analyte extraction and sample purification protocols with MOF sorbents allow for phosphate enrichment from aqueous matrices for isotopic analyses. The procedures developed in our work provide promising avenues for stable isotope analysis of phosphate and organophosphorus compounds with potential applications in studies of microbial metabolisms and the assessment of organophosphorus pollutant sources and transformation.

Besides being considered as a promising source of energy for the future, the physical and chemical properties of hydrogen are often used to resolve complex scientific questions. In the old days, scientists used off‐line vacuum lines, to generate hydrogen for dual-inlet-IRMS analyses. Waters were the first samples for 2H/1H determinations, then the evolution of techniques allowed applications to analyses of organic and inorganic matter. Various reduction techniques (U, Cr, V) were successfully developed. More recently, H2 was accessible to continuous flow techniques, especially using elemental analysers combined to EA-Py-IRMS techniques. Different types of reactors were developed to cover various types of hydrogen isotopic analyses (e.g. chromium reduction, glassy carbon pyrolysis). After a brief summary of technical evolutions, examples of applications for those techniques are presented. The first example is H analysis of refractory minerals where H is a trace element⁽¹⁾. Then a more recent illustration of the improvement for those techniques deals with analyses of δ²H from bone collagen (δ²H_coll), δ²H of tooth enamel (δ²H_enamel) and δ²H of bulk bone material (δ²H_bone) measured on specimens of humans, bovids, horses and a pig from the same archaeological site of Thézy-Glimont, France⁽²⁾. Samples have previously been studied using other isotopic proxies: δ¹⁸O, δ¹³C, δ¹⁵N and δ³⁴S.We show that similar interpretations can be made from the hydrogen isotope analysis of mineral tooth enamel (δ²H_enamel), which also provides information on children's dietary practices. These results open new prospects in a variety of research topics. Mineral body tissue δ²H is now a useful proxy associated to the already-used panel of isotopic tools.

(1) Fourel et al. 2017 RCM, Volume31,Issue24,Pages2066-2072,https://doi.org/10.1002/rcm.7996.

(2) Clauzel et al. 2022 Journal of Archaeological Science 147:105676. DOI: 10.1016/j.jas.2022.105676

Quantitative nuclear magnetic resonance (NMR) is commonly used to determine isotope ratios within molecules (irm-NMR, isotope ratio measured by NMR). While irm-NMR is well-developed for ¹³C and ²H, and to a lesser extent for ¹⁵N in position-specific isotope analysis (PSIA), existing methods often require hundreds of milligrams of material and lengthy experimental times.

To address these limitations, we explored the potential of ¹H NMR to determine the ¹⁵N isotope ratio, allowing position-specific nitrogen isotope analysis using only 5–30 mg of material. This new approach is the first demonstration of ¹H NMR measuring position-specific ¹⁵N isotope ratios within molecules. However, the detection of nitrogen-bound ¹H peaks requires specialised sample preparation, particularly for amino acids.

The method involves acquiring ¹H NMR spectra using a single-pulse sequence and quantifying the ¹H-¹⁴N and ¹H-¹⁵N peak areas by spectral deconvolution using an NMR fitting program. Initial tests on simple molecules, including ammonium chloride (NH₄Cl) and urea, established a calibration curve and demonstrated precision below 10‰ for both compounds. Trueness was achieved at <2‰ for NH₄Cl and <7‰ for urea, highlighting the potential of the method for more complex molecules such as amino acids. A poly-nitrogenous amino acid, tryptophan, was analyzed as a proof of concept.

In addition, we applied the method to a complex biological mixture—urine—to assess the PSIA of ¹⁵N in a real-world matrix. These results further validate the robustness of this approach for isotope ratio measurements in diverse and challenging samples.

This innovative method paves the way for highly sensitive and position-specific nitrogen isotope analysis in small sample quantities, opening new perspectives for the study of complex nitrogen compounds.

The McMaster Research Group for Stable Isotopologues (MRSI) is a leading research group whose mission is to remain at the forefront of stable isotope science through innovative research and discovery. Its primary research areas include: (1) “Developing and Refining Geochemical Proxies”, which involves using laboratory-grown minerals to better understand past and current environmental changes, (2) “Reconstructing Local and Global Climate Histories”, where researchers analyze natural samples of various origins to provide essential information for understanding past and modern climate trends, and (3) “Innovating Analytical Techniques for the Stable Isotope Community”, which focuses on developing new and improved methods for stable isotope users.

MRSI’s state-of-the-art research facilities enable high-quality stable isotope analyses and support the group’s groundbreaking research. Over the years, MRSI has made significant contributions to analytical techniques, enhancing the accuracy, precision, and efficiency of stable isotope measurements.

At the upcoming meeting, two recent analytical advances from MRSI will be presented, highlighting its ongoing efforts in analytical geochemistry. These advancements have the potential to further enhance the performance of stable isotope measurements for carbonate and water samples - the most common types of samples used by stable isotope researchers - and help researchers gain deeper insights into Earth's complex environmental systems.

Reducing nitrous oxide (N₂O) emissions of wastewater treatment is a pressing concern, as they dominate the sector's greenhouse gas footprint. N₂O is primarily produced during microbial denitrification and emitted to the atmosphere when N₂O reduction to atmospheric nitrogen (N₂) is limited. To reduce the climate impact of wastewater treatment the quantification of N₂O reduction, and related N₂ emissions, is essential. Here, we introduce a novel method to measure N₂ emissions from wastewater treatment based on the analysis of N₂/Ar ratios by quadrupole mass spectrometry (QMS) in a closed chamber setup. This novel approach is compared to on-line stable isotope analysis of the isotopic enrichment in residual N₂O emissions (¹⁴N¹⁵N¹⁶O, ¹⁵N¹⁴N¹⁶O, and ¹⁴N¹⁴N¹⁸O) by off-axis integrated cavity output spectroscopy (OA-ICOS) to estimate N₂ formation. Both measurement techniques were implemented on-site during anoxic treatment of wastewater at the Eawag pilot wastewater treatment plant in Dübendorf, Switzerland. We compare N₂ emission estimates by QMS, OA-ICOS, and an aqueous N-balance and discuss their applicability for full-scale plants. On-line quantification of N₂O reduction and N₂ emissions has the potential to guide the development of process optimization strategies to reduce N₂O emissions and mitigate the climate impact of wastewater treatment, while meeting increasingly stringent N discharge criteria.