Isotope Analysis Research Articles

Reply to the discussion and comments of Pestilho, A.L.S. and Mors, R.A. (2025) on the paper by Gomes et al. (2024). Early diagenetic evolution based on petrography and stable isotope analysis in the Barra Velha Formation of the Brazilian Pre‐salt. The Depositional Record, 1–25. https://doi.org/10.1002/dep2.288

Reply to the discussion and comments of Pestilho, A.L.S. and Mors, R.A. (2025) on the paper by Gomes et al. (2024). Early diagenetic evolution based on petrography and stable isotope analysis in the Barra Velha Formation of the Brazilian Pre‐salt. <i>The Depositional Record</i>, 1–25. https://doi.org/10.1002/dep2.288

Multiple Isotopes Reveal the Nitrate Sources in Aojiang River Basin, Eastern China.

Excessive nitrate (NO3-) in water poses a global environmental challenge. Identifying NO3- sources and their contributions is crucial for improving water quality. We collected surface water samples in the Aojiang River basin, Eastern China, during dry and wet seasons. Hydrochemical indicators, δ15N-NO3- and δ18O-NO3- were used to identify NO3- sources and assess their contributions. The findings revealed nitrification as the primary nitrogen transformation process. Isotopic analysis identified manure and sewage (M&S), soil nitrogen (SN), and nitrogen fertilizer (NF) as major NO3- contributors. The MixSIAR model analysis showed proportional contributions of atmospheric deposition (AD), NF, M&S, and SN to NO3- during the dry season as 2.84%, 19.63%, 44.67%, and 34.87%, respectively. In the wet season, the contributions were 3.61%, 22.32%, 32.37%, and 41.70%, respectively. This study enhances understanding of nitrogen sources and transformations in the Aojiang River basin, aiding better nitrogen contamination management.

Second generation ‘diamond-in-water’ ablation – a step forward in trace element and isotopic composition analysis

Abstract A second generation diamond-in-water laser ablation system combined with mass spectrometry measurements is presented for trace elements and radiogenic isotopic analyses of microinclusion-bearing diamonds. Ablation was conducted using a Nd: YV04 laser (532 nm, 136 µJ/pulse, 25 ns pulse duration, 2000 Hz repetition rate) in a closed ultra-clean glass cuvette filled with milli-Q water (18.2 MΩ cm). Multiple experiments indicate a highly stable and precise ablation process that proceeded at an average rate of 0.75 ± 0.41 mg/h. Triple Quadrupole inductively coupled plasma mass spectrometer (ICP-MS) trace element analyses of the ablated material reveal primitive mantle normalized patterns that are similar to previously analyzed microinclusion-bearing diamonds. Results comparable with previous ablation analyses of individual diamonds, and results of BHVO-2G and BCR-2G standards determined using this new ablation technique confirm its accuracy. Furthermore, the reference material results provide a means to estimate the uncertainty for the elemental concentrations in the diamonds, suggesting that it is generally below 10% for most elements of interest, and likely under 15% for all elements. The new ablation system produces enough material for successful Sr, Nd, and Pb isotope analyses by combined wet-chemistry and thermal ionization mass spectrometer (TIMS) using 1011 or 1013 Ω resistors. The Sr–Nd–Pb isotope values of BHVO-2G and BCR-2G ablated, purified using ion chromatography and measured by the same technique validate its accuracy. Low total procedural blank levels (Sr average of 71 ± 21 pg; Nd of 0.42 ± 0.25 pg Nd; Pb of 9.4 ± 3.6 pg) have little impact on the measured isotope values, but a blank correction can be applied if necessary.

The Geochemical Characteristics of Ore-Forming Fluids in the Jebel Stah Fluorite Deposit in Northeast Tunisia: Insights from LA-ICP-MS and Sr Isotope Analyses

The Geochemical Characteristics of Ore-Forming Fluids in the Jebel Stah Fluorite Deposit in Northeast Tunisia: Insights from LA-ICP-MS and Sr Isotope Analyses

Geochemical and Pb isotopic constraints on the provenance of the Lupa Capitolina bronze statue

Newly reanalyzed samples from the bronze statue of the Lupa Capitolina have provided lead isotope and trace element data. The lead isotope results coincide with those previously reported in the literature, but are approximately 20 times more precise. The high-resolution lead isotope analyses and the compositional data, especially lead concentrations higher than those found in copper ores, clearly reveal a mixing trend during the casting process. The addition of lead as a flux makes the lead isotopic composition unsuitable for determining the provenance of the bronze. However, comparisons with available data on bronze artifacts from the same epoch as the Lupa Capitolina statue (11th–12th centuries AD) support evidence of the monopolistic copper trade during the early Frankish and later Germanic imperial periods. Furthermore, element zoning in the Lupa Capitolina highlights details of successive melting within the metallurgical chaîne opératoire. Lead and other trace metals may have become enriched at the statue’s surface due to slow cooling after casting.

Archaeometric provenance study of marbles from Porphyreon and Chhim (Lebanon) and early Byzantine production specialisation

AbstractEarly Byzantine marble objects from Porphyreon and Chhim (Lebanon) were studied to assess the source of raw materials. In all, 66 artefacts, including elements of liturgical furnishings, architectural elements and daily use objects, were examined using optical, cathodoluminescence and scanning electron microscopy, X‐ray diffraction, and δ13C, δ18O, 87Sr/86Sr isotopic analyses. The results indicate that the marbles came mainly from the Prokonnesos and Dokimeion (Turkey). A distinct preference for specific marbles was observed in the production of particular object types and forms, such as chancel screens, table tops and mortars. This study offers the first insights into the specialisation of marble object production during the early Byzantine period.

The Chamrousse Ophiolite (Western Alps, France): Relict of a Devono‐Carboniferous Ocean

ABSTRACTThe Chamrousse ophiolite (Western Alps, France) is one of the best‐preserved Variscan relicts of Cambro‐Ordovician oceanisation within the northern Gondwana margin. This study presents new in situ U–Pb isotope analyses on zircon grains from that ophiolite, revealing that the oceanic stage in Chamrousse has occurred 150 Ma later than estimated. The metabasite unit, previously interpreted as the ophiolite volcanic layer, yields Cambro‐Ordovician zircon ages (460–520 Ma) with few Proterozoic inherited grains, suggesting a continental origin. Meanwhile, zircon grains from the ultramafic, gabbro and basaltic dike units yield new igneous U–Pb ages at 350–360 Ma. The Chamrousse ophiolite may thus be the relict of a marginal basin formed in a back‐arc setting, at the onset of the Variscan collision, as are other Devono‐Carboniferous ophiolites of the Variscan belt.

New insights from mercury isotopes of a No.3 coal in Tengnan Coalfield, Shandong Province, Eastern China: With emphasis on source of harmful trace elements

Mercury (Hg) is a critical pollutant in coal deposits, yet its sources and enrichment mechanisms remain debated. Mercury concentrations detected in ancient sedimentary deposits have frequently been employed as an indicator of volcanic activity, notably those associated with eruptions from large igneous provinces. Yet, this correlation requires careful evaluation, as multiple Hg sources may contribute to its enrichment in sedimentary environments. Potential Hg sources include volcanic emissions, hydrothermal fluids, anthropogenic activities, and other geogenic inputs. The examination of mass-dependent fractionation and mass-independent fractionation in laboratory experiments has increased the feasibility of employing mercury isotopic methodologies to deduce the origins of deleterious trace elements in environmental systems. The harmful trace elements Be, F, V, Cr, Cu, As, Se, Mo, Tl, Pb, U, and Hg show abnormal enrichment in the stratigraphic samples JY-3-1 and JY-3-9 from the Tengnan Coalfield. In the low-temperature hydrothermally altered coal seams of the Jinyuan Mine in southwestern Shandong Province, sulfide and clay minerals are likely the main carriers of mercury. This study aims to indirectly infer the sources of other harmful trace elements strongly correlated with mercury enrichment. A nuanced interpretation of Hg isotope data is necessary due to the complexity of multiple-source mixing, post-depositional modifications, and isotopic fractionation processes. Through the integration of mercury isotope analysis with a suite of analytical techniques, including geochemical analysis, mineralogical studies, and geological surveys, the results indicate that the sources of harmful trace elements in the No. 3 coal of the Jinyuan Mine are predominantly influenced by volcanic activity, atmospheric precipitation, and terrigenous sediment input, with a minor contribution from coal-forming plants. The application of Hg isotopes allows for more effective regulation of high-Hg coal usage, enabling policymakers to implement stricter emission controls, promote cleaner coal technologies, and establish Hg-specific air quality standards.

The origin of sulfur in Canary Island magmas and its implications for Earth’s deep sulfur cycle

The global sulfur cycle plays a critical role in the redox evolution of Earth's surface and upper mantle, yet the distribution and origin of sulfur in the mantle remains largely unconstrained. El Hierro is a volcanic island in the Canary archipelago that is fed by sulfur-rich magmas. To constrain the origin of sulfur in these melts, we combine in situ sulfur isotope analyses with regression modeling. We calculate that undegassed El Hierro melts have δ34S values of 0 ± 2‰. The average δ34S of undegassed El Hierro melts is 0.3‰ to 1‰ higher than magmas erupting at mid-ocean ridges. Mass balance calculations reveal that El Hierro's mantle source contains 310 ± 120 μg/g sulfur and that on average 60% of sulfur in the source is of recycled origin. This recycled material should contain >1,800 μg/g sulfur to satisfy isotopic constraints on its mass fraction in the mantle source. The sulfur and oxygen isotopic signature in serpentinites and sediments deviate significantly from the upper mantle, making them unsuitable candidates for the recycled material. An oxidized partial melt of recycled oceanic crust that retained one third of its sulfur budget after subduction zone processing can explain excess sulfur in the Canary Island mantle. Recycled oceanic crust is expected to contain sulfur as sulfide, which is not capable of oxidizing the mantle. The presence of ferric iron in the recycled component is necessary to produce metasomatic melts that are oxidizing enough to carry sufficient sulfur into the mantle source of ocean island basalts.

Through the Eyes of the Megafauna: Early Human Settlement and Isotopy in the South American Southern Cone

As humans expanded across the globe, the Americas were the last continents to be colonized. While debates persist regarding the timing and mechanisms of this process, it is widely accepted that by the Pleistocene–Holocene transition, the New World was populated from Alaska to Tierra del Fuego. During this period, hunter-gatherer societies demonstrated remarkable cultural and adaptive diversity, particularly in subsistence strategies and technological innovations. The colonization of the Americas offers valuable insights into population dynamics, human–environment interactions, species extinctions, and adaptive capacities. From an interdisciplinary perspective that combines an isotopic analysis of megafaunal remains with archaeological evidence, this study examines human interactions with Pleistocene fauna in the south–central region of South America’s Southern Cone. Isotopic analyses provide information about the diets, adaptations, and climatic challenges faced by megafaunal communities. Archaeological evidence reveals that humans utilized megafauna and other Pleistocene species for food and tool production. These findings are supported by evidence such as cut marks and bone tools, but also by sealed sediment layers and/or indisputable associations of lithic artifacts. This research contributes to our understanding of human dispersal in the Southern Cone during the colonization of the Americas, shedding light on the regional environments and adaptive strategies of early populations.

Modulation of the gut microbiota and the microbial-produced gut metabolites by diclofenac exposure and selenium supplementation.

Diclofenac (DCF) exposure is of great concern due to the ecotoxicological risk linked with a decline of vulture populations in Southeast Asia, but also because it can affect the reproduction and neurotoxicity in mammals. Otherwise, selenium (Se) is an antioxidant essential element with key roles in health and with antagonistic action against pollutants, but in some cases with a synergistic effect. To investigate the potential intertwined mechanisms between DCF, Se, and gut microbiota, gut metabolomic and gut microbiota profiles were determined in mice after DCF exposure and Se supplementation. Speciation of selenoproteins in plasma was carried out by isotopic dilution analysis to quantify the levels of selenoproteins. Significant differences in the levels of 79% of the gut metabolites were determined after DCF exposure. The most significant altered pathway in DCF and DCF-Se groups is the primary bile biosynthesis, being the only pathway altered in mice exposed to DCF, while in DCF-Se, the metabolism of galactose and linoleic acid is also altered. Moreover, specific associations between specific gut microbiota and metabolites were determined in the studied mice groups suggesting intertwined mechanisms. Selenium supplementation modulated the gut metabolic and microbiota profiles affected by DCF.

In Situ Geochemical and Sulfur Isotopic Composition of Pyrites from the Jiepailing Tin–Beryllium Polymetallic Deposit, Southern Hunan Province, China: Implications for Ore-Forming Processes

The Jiepailing deposit in southern Hunan is a typical large to super-large polymetallic tin deposit enriched in beryllium and other rare metals. To enhance the understanding of the mineralization processes of the Jiepailing deposit, detailed mineralogical, in situ geochemical, and sulfur isotopic analyses were conducted on pyrite closely associated with tin–polymetallic mineralization. Five types of pyrite have been identified in the deposit: (1) euhedral to subhedral medium- to coarse-grained pyrite (PyI) in tungsten–tin ore; anhedral fine-grained pyrite (PyII) in tin polymetallic–fluorite ore; anhedral fine-grained or aggregate pyrite (PyIII) in lead–zinc ore; euhedral to subhedral coarse-grained pyrite (PyIV) in beryllium–fluorite mineralization; and subhedral to anhedral fine-grained pyrite (PyV) in carbonate veinlets developed in the wall rock. Backscattered electron imaging indicates consistent structural features across the five types of pyrite. In situ trace element analysis reveals differences in trace element concentrations among the pyrite types. PyI is relatively enriched in Sn, Cu, and Co. In contrast, PyIII is enriched in Pb, Zn, Sn, and Ti, while PyIV and PyV are enriched in Ag and Sb. PyI has a Co/Ni ratio more than 1, while the Co/Ni ratios in the other four types of pyrite are less than 1. LA-MC-ICP-MS in situ sulfur isotope analysis shows δ34S values ranging from 2.5‰ to 5.8‰ (average 4.3‰, PyI), 2.5‰ to 5.8‰ (average 4.3‰, PyII), −7.6‰ to 9.5‰ (average 3.9‰, PyIII), −3.7‰ to 10.6‰ (average 3.6‰, PyIV), and 6.8‰ to 14.1‰ (average 9.2‰, PyV). Based on previous studies, regional geological background, deposit characteristics, and the in situ trace element and sulfur isotope compositions of pyrite, it is inferred that the various ore bodies in the Jiepailing deposit are products of Late Cretaceous magmatic–hydrothermal activity. The early ore-forming fluid originated from magmatic sources and during the migration into the wall rock and shallow formations, mixed with fluids primarily derived from atmospheric precipitation. Temperature, pressure, and composition changed of the ore-forming fluid which carried a large amount of substances, leading to tungsten–tin, tin polymetallic–fluorite, lead–zinc, and beryllium–fluorite mineralization, followed by carbonation during the late-stage mineralization.

Partial mycoheterotrophy in Apostasia wallichii, an early-diverging Asian tropical orchid.

All orchids exhibit mycoheterotrophy during their early development stages, which predisposes certain species to retain this nutritional mode into adulthood. Consequently, many orchids adopt partial mycoheterotrophy, a mixotrophic strategy combining carbon acquisition through both autotrophy and mycoheterotrophy. However, whether this strategy represents an ancestral trait remains contested. This study examines the fungal symbionts and nutritional strategies of the early-diverging orchid Apostasia wallichii and a sympatric, photosynthetic orchid, Cystorchis variegata, in tropical Asia (Sabah, Malaysian Borneo). Specifically, we explored their potential nutritional modes and mycobionts by analysing δ13C and δ15N isotopic profiles and employing high-throughput DNA sequencing. Community profiling via metabarcoding revealed that the A. wallichii individuals investigated were predominantly associated with putatively saprotrophic Botryobasidium fungi, while C. variegata was simultaneously associated with non-ectomycorrhizal rhizoctonias, saprotrophic non-rhizoctonia fungi, and ectomycorrhizal fungi. Additionally, stable isotope analysis showed that both A. wallichii and C.variegata were significantly enriched in 13C and 15N compared to co-occurring autotrophic plants, indicating partial mycoheterotrophy. Our findings, particularly the discovery of partial mycoheterotrophy associated with non-ectomycorrhizal fungi in A. wallichii, suggest that partial mycoheterotrophy in green orchids may be more widespread than previously believed and could represent an ancestral trait intrinsic to orchids.

Comparative Diets of Invasive Blue Catfish: Differences Across Rivers and Ontogenetic Stages

ABSTRACTBlue Catfish (Ictalurus furcatus) are an invasive species with expanding populations in freshwater systems, posing significant ecological challenges to native fauna. To assess their potential impacts in diverse aquatic ecosystems, we examined and compared the diets of non‐native Blue Catfish from four rivers in Georgia, USA, two of which drain into the Atlantic Ocean. A total of 936 Blue Catfish were collected from the Altamaha, Ocmulgee, Oconee, and Satilla rivers, with 90.38% of stomachs containing identifiable prey. Stomach content analysis revealed that Asian Clam (Corbicula fluminea) dominated their diet in terms of number (96.76%), weight (69.33%), and to a lesser degree, frequency (36.96%). Across rivers, smaller Blue Catfish (≤ 300 mm TL) had diets with a higher relative importance of insects and vegetation. Ontogenetic dietary trends showed increasing consumption of fishes and crustaceans as fish size increased in the Altamaha, Ocmulgee, and Oconee rivers. In contrast, the Satilla River population exhibited broader dietary diversity and distinct ontogenetic shifts. Stable isotope analysis (δ13C and δ15N) revealed significant differences between Blue Catfish from the Altamaha and Satilla rivers, underscoring their opportunistic feeding strategies in varying habitats. Bayesian niche overlap analysis indicated that size classes within the Altamaha and Satilla rivers had substantial intraspecific overlap, with Satilla subadults exhibiting the broadest niche (SEAB: 3.83). Factors such as prey availability, density dependence, and environmental conditions likely influence prey selection and feeding strategies in these systems. Understanding these dynamics is crucial for managing the ecological impacts of invasive Blue Catfish in freshwater systems of North America.

Isotopic variability of δ13C and δ15N signals in cave systems: insights from the blind tetra Astyanax mexicanus

Stable isotope analysis allows the study of element cycles in ecosystems and trophic ecology. δ13C reflects the diversity of primary productivity, while δ15N is a good indicator of trophic levels of organisms. Caves have limited resources due to the absence of light, reducing the trophic chains in these ecosystems. These extreme conditions impose strong selection pressures on cave-dwelling organisms, known as troglobites, which exhibit specific adaptations such as vision and pigment loss, and metabolic and physiological differences with their surface counterparts. The species Astyanax mexicanus corresponds to a model organism in the study of regressive evolution, which presents two different ecotypes, a widely distributed surface morph, and a cave-dwelling morph present in at least 34 caves in three karst regions of San Luis Potosí and Tamaulipas, Mexico. In the present study, we characterized the δ13C and δ15N of seven cave populations of A. mexicanus, corresponding to two karst regions: Sierra de El Abra and Sierra de Guatemala, representing distinct genetic cavefish lineages. We also developed a Nutrient Input Index (NI), to assess whether cave geomorphology influences resource availability. We found isotopic differences between caves and regions analyzed. Caves in the Sierra de El Abra showed higher δ15N values and wider trophic niche ranges compared with those in the Sierra de Guatemala, reflecting a more complex trophic network tentatively associated also with its geological history. In addition, a relationship was observed between the proximity of pools to the surface and the δ13C values, which could suggest differences in NI directly associated with cave geomorphology, impacting selective forces across the different cave systems.

A Long-Lasting, High-Stability Reactor System for Compound-Specific Carbon Isotope Analyses.

Compound-specific carbon isotope analysis is an essential technique in environmental, geobiological, ecological, and forensic research. It involvesthe online conversion of organic compounds separated by gas chromatography (GC) into carbon dioxide before entering a gas source mass spectrometer for carbon isotopic analysis. However, current oxidation interfaces require frequent maintenance or reactor replacement, reducing efficiency and data quality and increasing costs. This study presents a modified oxidation interface to address these issues. Our oxidation reactor system uses nickel and platinum wires as an oxidant with a constant oxygen flow controlled by an electronic pressure controller (EPC). This system eliminates the need for full-scale re-oxidation after initial activation and differs from systems using constant pressure control gauges that result in variable oxygen flow and carrier gas composition. We performed systematic comparisons of carbon isotope measurements for fatty acid methyl esters (FAMEs) and n-alkanes between our modified system and a commercial reactor system, and betweem systems that use constant pressure and constant flow oxygen supplies. Our oxidation interface with a constant flow of oxygen significantly enhances the analytical precision and accuracy of carbon isotope values, as demonstrated by a consistent reduction in the standard deviation of δ13C values to below 0.3‰. Importantly, our system has undergone over 5000 injections extending over 9 months during our longest analytical cycle, with no maintenance or user intervention needed. Our novel reactor system with a constant flow supply of auxiliary oxygen gas to the reactor greatly outperforms the conventional reactor system in efficiency, precision, and accuracy. It is virtually maintenance-free and may be dubbed the "forever" reactor, resulting in greatly enhanced analytical efficiency and reduced cost. Our methodology can be implemented on commercial systems with straightforward modifications by users.

Employing hydrogen stable isotope analysis for traceability of invasive pine wood nematode vector insects.

Bursaphelenchus xylophilus, the pathogen responsible for pine wilt disease, significantly threatens pine forests globally, with rapid infection leading to tree mortality within 40 days. This disease spreads efficiently through vector beetles, with Monochamus alternatus and Monochamus saltuarius serving as the primary vectors and Monochamus galloprovincialis being considered a potential vector in China. Molecular traceability and stable isotope traceability are both important techniques for insect tracing, each with its own advantages and limitations. Molecular traceability, such as DNA-based methods, offers high specificity and accuracy in identifying insect species, but it may require more complex procedures and higher costs due to the need for advanced equipment and skilled personnel. Stable isotope tracing, however, provides conservative and high-precision signatures, and is label-free, making it suitable for tracing the origins and pathways of insects in complex environments. Using the method of degreasing, the fat of the sample epidermis was removed, only the bone part was left, and the abdominal cavity was emptied to prevent the food from affecting the determination of hydrogen isotope. The present study aimed to trace the geographic origins of these vector insects in China using hydrogen stable isotope ratios, providing a novel tool for disease management. Data processing and modeling were conducted using R and Origin software, yielding the equation y = 0.9822x + 19.1765. Statistical tests confirmed the model's significance and fit. Results indicate a significant positive correlation of temperature and precipitation with atmospheric hydrogen isotopic composition. Our findings demonstrate the model's applicability in tracking the spread of pine wilt vectors, offering a promising approach to forest pathogen management. If the sample isotope test value is brought into the model and marked in the partition diagram, it can be proved that the model can effectively identify the source information of the sample. © 2025 Society of Chemical Industry.

Hydrochemical insights into spatiotemporal characteristics of groundwater salinization and health risk assessment of fluoride in the south bank of Yellow River irrigation area, Northwest China.

The groundwater salinization problem in the south bank of the Yellow River irrigation area is severe, restricting the sustainability of groundwater resources. However, the groundwater salinization formation mechanism is unclear. Accordingly, this study analyzed the chemical characteristics and salinization mechanism of groundwater based on hydrochemical analyses (self-organizing maps, SOM), isotope analyses (δ18O and δD), and quantitative models (Rayleigh distillation model), as well as evaluating the potential health risks of fluoride. The results indicated that surface water and groundwater in the study area had high salinity and weak alkalinity, with the fluoride and total nitrogen (TN) content exceeding Grade III water standards. Additionally, only 42% of the water samples were suitable for drinking, with nitrogen sources being the main cause of water quality deterioration. Around half of the samples were unsuitable for irrigation. The spatial and temporal distribution of total dissolved solids (TDS) in the irrigation area was influenced by autumn irrigation. Overall, groundwater salinization was primarily attributed to evaporite dissolution, cation exchange, silicate weathering, and human inputs. Evaporation was not the main influencing factor. In addition, the non-carcinogenic risk of fluoride in the water body decreased as follows: infants > children > adult females > adult males. The results of this study deepen understanding of the relationship between changes in groundwater quality and the ecological environment in semi-arid inland areas, thereby promoting the rational utilization and scientific management of groundwater resources in the irrigation area.

Chemical Durability of Uranium Oxide Microspheres for Use as QC Materials for Nuclear Safeguards.

This study investigates the chemical durability of uranium oxide microparticles (UO2+x and U3O8), as potential reference materials for nuclear safeguards. To optimize long-term preservation, the particles were exposed to three different storage media: dilute nitric acid (10-2 mol L-1 HNO3), deionized water, and ethanol. Dissolution rates in nitric acid (∼5 × 10-4 g.m-2.d-1) were similar to those of bulk uranium oxides, but UO2+x particles experienced greater absolute leaching due to their higher specific surface area, resulting in noticeable morphological changes. In distilled water, rapid precipitation of secondary phases, such as schoepite and studtite, transformed the particle morphology into aggregated platelets. In contrast, ethanol preserved both particle shape and structural integrity over 8 months, ensuring stability for isotopic analysis using large geometry secondary ion mass spectrometry (LG-SIMS). These results suggest ethanol as the most effective storage medium, especially under anhydrous conditions. While both UO2+x and U3O8 exhibited comparable durability, their reactivity was primarily influenced by microstructural differences. This study highlights the importance of selecting appropriate storage conditions based on fabrication methods and particle characteristics to maintain uranium oxide reference materials for nuclear safeguards and ensure their long-term reliability in quality control applications.

Determination of KGa‐1b and SHCa‐1 Δ′17O and δ18O via Laser Fluorination of Lithium Fluoride Clay Pellets

ABSTRACTRationaleStable oxygen isotope measurements in silicate clays, such as smectite and kaolinite, provide crucial information for understanding Earth's climate history and environmental changes. Despite a growing interest in the oxygen isotope analysis of silicate clays and clay‐rich sediments, there lacks a consensus on the preparation and standardization of clay mineral samples. To improve the accuracy and interlaboratory comparisons of clay isotope measurements, especially those involving laser fluorination techniques, newly established kaolinite and smectite oxygen isotope standards are much needed.MethodsWe employed conventional nickel bomb fluorination combined with dual‐inlet isotope ratio mass spectrometry to establish precise δ18O and Δ′17O values for leached clay reference materials KGa‐1b and SHCa‐1, a kaolinite and a hectorite/smectite, respectively. We further measured leached KGa‐1b and SHCa‐1 pressed into pellets with a lithium fluoride as a binding agent for the laser fluorination method, allowing us to test the reproducibility between methods and utilize a standard laser chamber drift correction scheme.ResultsThe laser fluorination technique yielded highly precise and reproducible δ18O and Δ′17O measurements for the KGa‐1b and SHCa‐1, aligning with bomb values of δ18O. This confirms the method's reliability and comparability to conventional isotope measurement techniques while also stressing the importance of proper sample preparation and laser chamber drift corrections.ConclusionsThis study demonstrates that laser fluorination is an effective method for accurately measuring the stable oxygen isotope composition of silicate clays or clay‐rich sediments when corrected with known silicate clay standards. These methods offer a valuable methodology for future research and applications that will significantly improve our understanding of past climate and environmental conditions.