Isotope Laboratory Research Articles

Oxygen and Carbon Isotopes in Marine Carbonates: A Biogenic Climate Archive Built Upon Disequilibria

The stable isotopic composition of marine biogenic carbonates is one of the main archives for paleoclimate reconstructions. Reading these archives accurately requires understanding of how different organisms make carbonate minerals, and how various biomineralization processes influence stable isotope fractionation. New developments in stable isotope measurements, laboratory experiments, and biomineralization modeling have progressively enabled us to disentangle the environmental and biological controls on the stable isotope proxies, and offer promise for a deeper understanding of how calcifying organisms record and respond to changes in Earth’s climate and carbon cycle through geologic time.

PETRÁNYI GYULA BELGYÓGYÁSZ PROFESSZOR, A DEBRECENI ORVOSTUDOMÁNYI EGYETEM INTÉZMÉNYVEZETŐ DÉKÁNJA 1953-1954

In the academic year 1953/54, Professor Gyula Petrányi headed the Debrecen Medical University, which became independent in 1951, as Dean with the power of a rector, and then served as Vice-Rector of the Clinical Faculty of the University from 1971-74. He came to the University of Debrecen in 1950 at the young age of 38, when he was entrusted with the establishment and organization of the II. Department of Internal Medicine. Initially, the clinic was located in Bem Square within the Municipal Hospital, then moved to the clinical premises in July 1951. From 1967 to 1974 he was director of the I. Department of Internal Medicine. Until 1983, he was head of the Internal Medicine Clinic II at Semmelweis Medical University and, at the same time director of the National Institute of Internal Medicine. During his 24 years in Debrecen, he drew on his previous international experience to establish a new clinic that was up to date. He laid the foundations for an integrated approach to internal medicine and sub-disciplinary specialization. His repeatedly published textbooks on internal medicine have underpinned the knowledge and professional work of generations of medical doctors. He is credited with the establishment of the Immunology Laboratory, the Isotope Laboratory, the Intensive Care Unit of the Department of Internal Medicine, the Endoscopy Laboratory, the Dialysis Centre, and the foundation of the Central Clinical Chemistry Laboratory. In his scientific activity, he focused on immunology, which was a pioneering field at the time, and as an academician, he laid the clinical foundations for this field in Hungary. His university leadership was characterized by systemic and quality elevation of teaching, clinical and research activities. As dean and clinical deputy rector, he played a significant role in the Medical University of Debrecen serving as an example for other Hungarian medical universities.

Spatial and temporal stable water isotope data from the upper snowpack at the EastGRIP camp site, NE Greenland, sampled in summer 2018

Abstract. Stable water isotopes stored in snow, firn and ice are used to reconstruct climatic parameters. The imprint of these parameters at the snow surface and their preservation in the upper snowpack are determined by a number of processes influencing the recording of the environmental signal. Here, we present a dataset of approximately 3800 snow samples analysed for their stable water isotope composition, which were obtained during the summer season next to the deep drilling site of the East Greenland Ice Core Project in northeast Greenland (75.635411° N, 36.000250° W). Sampling was carried out every third day between 14 May and 3 August 2018 along a 39 m long transect. Three depth intervals in the top 10 cm were sampled at 30 positions with a higher resolution closer to the surface (0–1 and 1–4 cm depth vs. 4–10 cm). The sample analysis was carried out at two renowned stable water isotope laboratories that produced isotope data with the overall highest uncertainty of 0.09 ‰ for δ18O and 0.8 ‰ for δD. This unique dataset shows the strongest δ18O variability closest to the surface, damped and delayed variations in the lowest layer, and a trend towards increasing homogeneity towards the end of the season, especially in the deepest layer. Additional information on the snow height and its temporal changes suggests a non-uniform spatial imprint of the seasonal climatic information in this area, potentially following the stratigraphic noise of the surface. The data can be used to study the relation between snow height (changes) and the imprint and preservation of the isotopic composition at a site with 10–14 cm w.e. yr−1 accumulation. The high-temporal-resolution sampling allows additional analyses on (post-)depositional processes, such as vapour–snow exchange. The data can be accessed at https://doi.org/10.1594/PANGAEA.956626 (Zuhr et al., 2023a).

The absolute δ18 O value for SLAP with respect to VSMOW reveals a much lower value than previously established.

SLAP is one of the two calibration materials for the isotopic water scale. By consensus the established δ18 O value is -55.5‰, although several expert laboratories measure significantly more negative δ18 OSLAP values. The real δ18 OSLAP value as such does not influence the isotopic water scale; however, knowledge of the size of isotopic scale contraction in stable isotope measurements is vital for second-order isotopes. This study describes the quantification of δ18 OSLAP with respect to δ18 OVSMOW . SLAP-like water was quantitatively mixed with highly 18 O-enriched water to mimic VSMOW. The 18 O concentration was determined using an electron ionization quadrupole mass spectrometer. The isotopic composition of the SLAP-like and VSMOW-like waters was measured using an optical spectrometer, alongside original VSMOW and SLAP. This study resulted in a much more negative δ18 O value for SLAP than expected. The averaged outcome of seven independent experiments is δ18 OSLAP = -56.33 ±0.03‰. There is a large discrepancy between the actual isotopic measurements of even the most carefully operating isotope laboratories and the true δ18 O value. Although this finding as such does not influence the use of the VSMOW-SLAP scale, it raises the intriguing question of what we actually measure with our instruments and why even a fully corrected measurement can be so far off. Our result has consequences for issues like the transfer of δ18 O from and to the VPDB scale, various fractionation factors, and Δ17 O. The absolute 18 O abundance for SLAP was calculated as (1887.98 ± 0.43) × 10-6 based on the absolute 18 O abundance of VSMOW and the presented δ18 OSLAP in this paper.

Evaluation of exposure to ionizing radiation of medical staff performing procedures with glucose labeled with radioactive fluorine - 18F-FDG

Evaluation of exposure to ionizing radiation of medical staff performing procedures with glucose labeled with radioactive fluorine - 18F-FDG

Effects of lipid extraction on human bone collagen: Comparing stable carbon and nitrogen isotope values with and without lipid extraction

Effects of lipid extraction on human bone collagen: Comparing stable carbon and nitrogen isotope values with and without lipid extraction

Indigenous artefacts and oral stories

This article presents the results of studies conducted by Canadian academics in collaboration with Sturgeon Lake and Pelican Narrows First Nations communities (Saskatchewan, Canada). The objectives of the project were: (1) developing a research ethics protocol for collecting, studying, and preserving indigenous artefacts; (2) measurements of chemical compositions of artefacts; (3) collecting oral stories of Elders. Within the project, two workshops were organized in Pelican Narrows and Sturgeon Lake. Post-secondary students were trained to work on the project. The laboratory measurements of chemical compositions of artefacts were conducted at the Scanning Electron Microscope Laboratory (University of Alberta), and the Saskatchewan Isotope Laboratory (University of Saskatchewan). The carbon-dating measurements were carried out at André E. Lalonde Accelerator Mass Spectrometry Laboratory (University of Ottawa). The statistical analysis of chemical compositions was conducted in order to test the provenance similarities of artefacts. The project was supported by the Department of Canadian Heritage.

Studies of Physical Parameters of Indigenous Artifacts. Collecting and Preserving the Relating Oral Stories

The project, supported by the Department of Canadian Heritage, was conducted by scholars from First Nations University of Canada (FNUniv), University of Regina (U of R) and Royal Saskatchewan Museum (RSM) in 2018 - 2020, in collaboration with Sturgeon Lake and Pelican Narrows First Nations communities. More than forty people, including Elders and students, participated in this project. The research Ethics review was done by U of R. We also consulted with Elders regarding the research Ethics protocols during the individual meetings, ceremonies and workshops in Pelican Narrows and Sturgeon Lake. Research assistants (Indigenous students) were trained (Indigenous studies and the basics of archaeology) for working in First Nations communities and at the RSM. We interviewed Elders and Knowledge Keepers from Pelican Narrows and Sturgeon Lake and recorded their oral stories; collected Indigenous artifacts in these communities and selected samples from RSM collections for physical measurements at the Scanning Electron Microscope Laboratory of the University of Alberta, Saskatchewan Isotope Laboratory of the University of Saskatchewan and André E. Lalonde Accelerator Mass Spectrometry Laboratory of the University of Ottawa. Then we carried out the statistical analysis of the obtained data. The preliminary results of the project were presented to community members.

Study of associations of blood proteins with development of unstable atherosclerotic plaques in coronary arteries by quantitative proteomics

Aim. To study the associations of blood proteins with the presence of unstable atherosclerotic plaques in the arteries in patients with coronary artery disease using the quantitative proteomic analysis.Materials and methods. The study included patients with coronary artery disease (n = 40); the average age of patients was 58 ± 7 years. Material for the study was blood serum. Protein concentrations in serum samples were determined using the PeptiQuant Plus Proteomics Kit (Cambridge Isotope Laboratories, USA). Protein fractions were identified using the liquid chromatograph and tandem mass spectrometer Q-TRAP 6500.Results. Mass spectrometry revealed an increased concentration of proteins, such as fibrinogen, fibulin-1, and complement factor H, in the serum samples of patients with unstable atherosclerotic plaques. It took place with a simultaneous decrease in the levels of α 2-antiplasmin, heparin cofactor II, coagulation factor XII, plasminogen, prothrombin, vitronectin, complement proteins (C1, C3, C7, C9), and complement factor B. The differences were considered significant at p < 0.05. It was revealed that the presence of unstable atherosclerotic plaques was associated with the level of fibulin-1 (Exp(B) = 1.008; р = 0.05), plasminogen (Exp(В) = 0.995; р = 0.027), and coagulation factor X (Exp(В) = 0.973; р = 0.037).Conclusion. An increased concentration of fibulin-1 can be considered as a potential biomarker of unstable atherosclerotic plaque development in coronary artery disease. The possibility of using the studied proteins as biomarkers of unstable atherosclerotic plaques requires further studies on their potential role in the development of this disease.

PSXI-12 Determination of Protein Requirements for Labrador Retriever Pups (> 14 wk-9 Mo) Using the Indicator Amino Acid Oxidation (Iaao) Technique

Abstract Providing protein to growing puppies in accurate amounts ensures that animals have enough energy and nutrients for depositing muscle, growing bones, and maintaining joint health. Inclusion amounts must be provided at correct doses, considering a diet with excess protein can lead to harmful outcomes such as hyperkalemia or acidosis. To determine the protein requirements in growing Labrador Retrievers, the indicator amino acid oxidation (IAAO) technique was utilized in six puppies (>14 wk-9 mo). Dogs were supplied with constant dietary Phe across diets. The control diet was fed for two days, followed by a day in which the test diet was fed, a tracer amino acid was supplied, and breath samples were collected. On test day, a priming dose of L-[1-13C]phenylalanine (Cambridge Isotope Laboratories, Inc.) based on the body weight of the subject was supplied, followed by [1-13C]Phe doses every 30 minutes, spanning a four-hour period. A respiration mask was placed on each subject every 30 minutes (Oxymax, Columbus Instruments), 13CO2 was collected, and enrichment was determined by isotope ratio mass spectrometry (IRMS). IRMS results were converted to atom percent excess (APE) and analyzed using a segmented model of best fit (JMP Pro 16). The outcome of this experiment determines that if essential amino acids and non-essential amino acid nitrogen requirements are met, Labrador Retriever puppies will have mean and population safe requirements (mean±2SD) of 47.5 ± 1.325 g/1,000 kcal.

PSXIII-B-3 Determining Phenylalanine and Tyrosine Amino Acid Requirements in Growing Labrador Retrievers Using the Direct Amino Acid Oxidation Technique

Abstract Phenylalanine and tyrosine are important amino acids for synthesis of proteins, catecholamine neurotransmitters, and melanin in canines. Since phenylalanine (Phe) is converted to tyrosine (Tyr), this experiment used the direct amino acid oxidation (DAAO) technique to determine the phenylalanine requirement and phenylalanine plus tyrosine requirements for growing Labrador Retrievers. The Phe requirement was separated from Phe plus Tyr requirement by supplementing the test diets utilized for Phe requirements with 1.48% crystalline Tyr. A total of twelve dogs were used in two trials to determine the Phe and Phe + Tyr requirements in growing puppies ( >14wk-1yr). Control diet was fed for two days, followed by a testing day where an experimental diet was fed, a tracer amino acid was supplied, and breath samples were collected. On test day, a priming dose of L-[1-13C] phenylalanine (Cambridge Isotope Laboratories, Inc.) based on the dog’s body weight was supplied, followed by enteral feeding of [1-13C]Phe every 30 minutes, spanning a four hour period. Respiration masks were placed on each subject every 30 minutes (Oxymax, Columbus Instruments), 13CO2 collected, and enrichment determined by isotope ratio mass spectrometry (IRMS). Results for IRMS were converted to atom percent excess (APE) and analyzed using a segmented model (JMP® Pro 15). Results showed that Phe mean and population safe requirements were 1.29 +/- 0.26 g/1000 kcal, while the Phe + Tyr requirements were 1.95 +/- 0.65 g/1000 kcal. Knowledge gathered through these studies is invaluable as both the Phe and Phe plus Tyr dietary requirements for growing Labrador Retriever puppies were determined.

Design and radiological study of the 225Ac medical target at the TRIUMF-ARIEL proton-target station

Design and radiological study of the 225Ac medical target at the TRIUMF-ARIEL proton-target station

Design optimization of an electron-to-photon conversion target for ultra-high dose rate x-ray (FLASH) experiments at TRIUMF

Objective. To develop a bremsstrahlung target and megavoltage (MV) x-ray irradiation platform for ultrahigh dose-rate (UHDR) irradiation of small-animals on the Advanced Rare Isotope Laboratory (ARIEL) electron linac (e-linac) at TRIUMF. Approach. An electron-to-photon converter design for UHDR radiotherapy (RT) was centered around optimization of a tantalum–aluminum (Ta–Al) explosion-bonded target. Energy deposition within a homogeneous water-phantom and the target itself were evaluated using EGSnrc and FLUKA MC codes, respectively, for various target thicknesses (0.5–1.5 mm), beam energies (E e− = 8, 10 MeV) and electron (Gaussian) beam sizes ( = 2–10 mm). Depth dose-rates in a 3D-printed mouse phantom were also calculated to infer the compatibility of the 10 MV dose distributions for FLASH-RT in small-animal models. Coupled thermo-mechanical FEA simulations in ANSYS were subsequently used to inform the stress–strain conditions and fatigue life of the target assembly. Main results. Dose-rates of up to 128 Gy s−1 at the phantom surface, or 85 Gy s−1 at 1 cm depth, were obtained for a 1 × 1 cm2 field size, 1 mm thick Ta target and 7.5 cm source-to-surface distance using the FLASH-mode beam (E e− = 10 MeV, 2 = 5 mm, P = 1 kW); furthermore, removal of the collimation assembly and using a shorter (3.5 cm) SSD afforded dose-rates >600 Gy s−1, albeit at the expense of field conformality. Target temperatures were maintained below the tantalum, aluminum and cooling-water thresholds of 2000 °C, 300 °C and 100 °C, respectively, while the aluminum strain behavior remained everywhere elastic and helped ensure the converter survives its prescribed 5 yr operational lifetime. Significance. Effective design iteration, target cooling and failure mitigation have culminated in a robust target compatible with intensive transient (FLASH) and steady-state (diagnostic) applications. The ARIEL UHDR photon source will facilitate FLASH-RT experiments concerned with sub-second, pulsed or continuous beam irradiations at dose rates in excess of 40 Gy s−1.

CANREB EBIS commissioning at TRIUMF

The Canadian Rare Isotope facility with Electron Beam ion source (CANREB) is an essential part of the Advanced Rare IsotopE Laboratory (ARIEL) presently under construction at TRIUMF. CANREB was recently commissioned and can accept stable or rare isotope beams from a variety of ion sources, delivering high purity beams of highly charged ions (HCI) to experiments. The injected beams are bunched using a radiofrequency quadrupole cooler-buncher and energy adjusted using a pulsed drift tube for injection into the electron beam ion source (EBIS) charge state breeder. The EBIS is designed for a maximum electron beam current of 500 mA and a maximum magnetic field of 6 T. Ions with energies up to 14 keV can be injected and HCI with mass-to-charge (A/q) ratios 3 ⩽ A/q ⩽ 7 can be charge bred and extracted. The HCI are A/q-selected using a Nier-type spectrometer before being transported to the ISAC linac for post-acceleration. Results from CANREB beam commissioning with focus on the EBIS will be presented.

Progress and challenges in dual- and triple-isotope (δ18 O, δ2 H, Δ17 O) analyses of environmental waters: An international assessment of laboratory performance.

Stable isotope analyses of environmental waters (δ2 H, δ18 O) are an important assay in hydrology and environmental research with rising interest in δ17 O, which requires ultra-precise assays. We evaluated isotope analyses of six test water samples for 281 laboratory submissions measuring δ2 H and δ18 O along with a subset analyzing δ17 O and Δ17 O by laser spectrometry and isotope ratio mass spectrometry (IRMS). Six test waters were distributed to laboratories spanning a wide δ range of natural waters for δ2 H, δ18 O and δ17 O and Δ17 O. One sample was a blind duplicate to test reproducibility and claims of analytical precision. Results showed that ca 83% of the submissions produced acceptable δ18 O and δ2 H results within 0.2‰ (mUr) and 1.6‰ of the benchmark values, respectively. However, 17% of the submissions gave questionable to unacceptable results. A blind duplicate revealed many laboratories reported overly optimistic precision, and many could not replicate within their claimed precision. For Δ17 O, dual-inlet results for IRMS using quantitative O2 conversion were accurate and highly precise, but the results for laser spectrometry ranged by ca 200 per meg (μUr) for each sample, with ca 70% unable to replicate the duplicate to their claimed Δ17 O precision. One complicating factor is the lack of certified primary reference waters for δ17 O. No single factor or combination of factors was identifiable for poor or good performance, and underperformance came from issues like data normalization including inadequate memory and drift corrections, compromised working reference materials and underperforming instrumentation. We recommend isotope laboratories include high and low δ value controls of known isotope composition in each run. Progress in Δ17 O analyses by laser spectrometry requires extraordinary proof of performance claims and would benefit from the development of adoptable and systematic advanced data processing procedures to correct for memory and drift.

PSX-A-5 Late-Breaking: Branched chain amino acid and threonine requirements for puppy (>14 wk-9mo) Labrador Retrievers using the indicator amino acid oxidation (IAAO) technique

Abstract Branched chain amino acids are heavily involved in protein synthesis and turnover, emphasizing the need to establish requirement for growing animals. On the other hand, threonine is vital for supporting proteins necessary for gut health. Thus, it is very important to supply branched chain amino acids and threonine in appropriate amounts to growing animals. In this experiment, the indicator amino acid oxidation (IAAO) technique was utilized to determine valine, isoleucine, leucine, and threonine requirements in six puppy Labrador Retrievers (>14wk-9mo). Puppies were subjected to diets ranging from deficient to excess, with each of the indispensable amino acids formulated at 1.6x NRC values. The control diet was fed for two days of adaptation, followed by one experimental day in which the test diet was fed. On the test day, a breath sample was collected using a using a respiration mask (Oxymax, Columbus Instruments). A priming dose of L-[1-^13C]phenylalanine (Cambridge Isotope Laboratories, Inc.) based on body weight was supplied to each puppy, followed by [1-^13C]Phe doses every 30 minutes, for a four hour period. ^13CO[2] was collected after each dose and enrichment was determined by isotope ratio mass spectrometry (IRMS). Results from IRMS were converted to atom percent excess (APE) and analyzed using a segmented line model (JMP^® Pro 16). Each of the Four Rivers mean and population requirements were as follows: 1.72 ± 0.11 g/1000 kcal ME for valine; 1.43 ± 0.24 g/1000 kcal ME for isoleucine; 2.25 ± 0.15 g/1000 kcal ME for leucine; 1.74 ± 0.16 g/1000 kcal ME for threonine (mean ± 2SD). The knowledge gained from this study is highly useful as the lean mass deposited as a puppy influences the animal throughout their lifetime.

PSX-A-17 Late-Breaking: Methionine and total sulfur amino acid requirements for pups (>14 wk to 9 months), adults, and senior Labrador Retrievers using the indicator amino acid oxidation (IAAO) technique

Abstract Methionine and cystine are often considered limiting amino acids in canine diets but limited requirement studies have been conducted especially for different life stages. Eighteen Labrador Retrievers (6 pups (>14 wk-9 month), 6 adults, and 6 seniors [>8yr)] were utilized in feeding studies to evaluate the changing requirements of methionine (Met) and total sulfur amino acids (TSAA) as canines age. For this study, the indicator amino acid oxidation (IAAO) technique was utilized to determine the amino acid (AA) requirements in each of the three age groups. Dogs were subjected to diets ranging from deficient to excess, with indispensable amino acids formulated at 1.6x NRC values. To allow for adaptation, a control diet with same dietary ingredients, protein and amino acid levels was fed for two days prior to feeding the test diets on the third day. On test day, a baseline breath sample was collected for determining CO2 production using a respiration mask (Oxymax, Columbus Instruments). A priming dose of L-[1-13C] phenylalanine (Cambridge Isotope Laboratories, Inc.) based on body weight was utilized, followed by [1-13C] Phe doses every 30 minutes, spanning a four hour period. After each dose 13CO2 was collected, and enrichment was determined by isotope ratio mass spectrometry (IRMS). Results for IRMS were converted to atom percent excess (APE) and analyzed using a piecewise model of best fit (JMP® Pro 16). A segmented line regression showed Met and TSAA mean and population requirements for pups (>14 wk-9 mo.) were 0.78 ± 0.16 and 1.53 ± 0.21 g/1000kcal (mean ± 2SD), respectively. Meanwhile, for adults, mean and population requirements for Met and TSAA were estimated to be 0.68 ± 0.19 and 1.4 ± 0.30 g/1000kcal (mean ± 2SD), respectively, and for seniors, Met and TSAA mean and population requirements were determined to be 0.62 ± 0.17 and 1.27 ± 0.23 g/1000kcal (mean ± 2SD), respectively.

Population structure, habitat preferences, feeding strategies, and diet of the brittle star Ophiopholis aculeata in nearshore and offshore habitats of the northwest Atlantic

AbstractOphiopholis aculeata is a ubiquitous brittle star (Echinodermata: Ophiuroidea) known to occur from the upper subtidal to the bathyal zone. Individuals from shallow inshore habitats (rhodolith beds and rock fields) and deeper offshore locations in eastern Canada were studied to assess the population structure, habitat selection, diet, and feeding strategies of this species through use of stable isotope analyses, gut contents, and laboratory experiments. Potential drivers of habitat selection such as depth, light conditions, body size, sex, intraspecific competition, and presence of predators were examined. This study highlighted variable population size structures and abundances as well as diversified food sources and feeding strategies (i.e., suspension and deposit feeding, scavenging, predation on live organisms, and even cannibalism) as a function of native depth and habitat. It also revealed that studies on the feeding biology of brittle stars must carefully consider sex and life stage as driving factors.

Rhyolitic and basaltic reference materials for TC/EA analysis: Investigation of water extraction and D/H ratios

Rhyolitic and basaltic reference materials for TC/EA analysis: Investigation of water extraction and D/H ratios

Performance of low-cost stainless-steel beverage kegs for long-term storage integrity and easy dispensing of water isotope (δ18 O, δ2 H) reference materials.

A widespread problem observed in global water isotope (δ18 O, δ2 H) proficiency tests is compromised working reference materials due to storage-dispensing evaporation effects. Proper storage requires no evaporation or leakage, which causes isotopic drift and bias. Surveys by the International Atomic Energy Agency (IAEA) show most isotope laboratories use glass or plastic bottles to store working reference materials, with frequent opening and closings that pose evaporation risks. Practical small (ca. 2-5 L) storage-dispensing solutions free of air exposure, evaporation, and leakage are needed. We also tested several smaller-scale bottles for day-to-day aliquots. We tested low-cost, conveniently sized (4 L) adaptations of a common stainless-steel beverage keg with a liquid dispenser, with minor modifications to facilitate low-flow dispensing and pressurization (1-2bar) with Ar or N2 . We tested three kegs (100%, 75%, 50% initial fills) for a 2-year period along with monthly dispensing to assess long-term storage viability for maintaining δ18 O and δ2 H integrity and dispensing, and day-to-day aliquot bottles for 6months. Test results showed these small keg storage systems fully maintained the isotopic integrity of water over the 2-year testing period with no trend in the isotopic data that would reveal evaporative loss or leakage (e.g., pressure or mass loss) regardless of starting fill level. However, evaporated water in the outlet tube assembly must be eliminated by discarding 15-20 mL before dispensing into appropriate daily-use laboratory standard bottles (30-100 mL). Glass bottles for daily aliquots showed good integrity properties, but only if their fill level was >50%. The use of a low-cost pressurized metal beverage keg dispensing system provides a robust solution to enable laboratories to maintain the integrity of their water isotope working reference materials over several years.