Isotope Ratio Measurements Research Articles

Coral photosymbiosis on Mid-Devonian reefs.

The ability of stony corals to thrive in the oligotrophic (low-nutrient, low-productivity) surface waters of the tropical ocean is commonly attributed to their symbiotic relationship with photosynthetic dinoflagellates1,2. The evolutionary history of this symbiosis might clarify its organismal and environmental roles3, but its prevalence through time, and across taxa, morphologies and oceanic settings, is currently unclear4-6. Here we report measurements of the nitrogen isotope (15N/14N) ratio of coral-bound organic matter (CB-δ15N) in samples from Mid-Devonian reefs (Givetian, around 385 million years ago), which represent a constraint on the evolution of coral photosymbiosis. Colonial tabulate and fasciculate (dendroid) rugose corals have low CB-δ15N values (2.51 ± 0.97‰) in comparison with co-occurring solitary and (pseudo)colonial (cerioidor phaceloid) rugose corals (5.52 ± 1.63‰). The average of the isotopic difference per deposit (3.01 ± 0.58‰) is statistically indistinguishable from that observed between modern symbiont-barren and symbiont-bearing corals (3.38 ± 1.05‰). On the basis of this evidence, we infer that Mid-Devonian tabulate and some fasciculate (dendroid) rugose corals hosted active photosymbionts, while solitary and some (pseudo)colonial (cerioidor phaceloid) rugose corals did not. The low CB-δ15N values of the Devonian tabulate and fasciculate rugose corals relative to the modern range suggest that Mid-Devonian reefs formed in biogeochemical regimes analogous to the modern oligotrophic subtropical gyres. Widespread oligotrophy during the Devonian may have promoted coral photosymbiosis, the occurrence of which may explain why Devonian reefs were the most productive reef ecosystems of the Phanerozoic.

Online Isotope Analysis of Sulfur in Proteins via Capillary Electrophoresis Coupled With Multicollector ICP-MS (CE/MC-ICP-MS): A Proof of Concept Study.

Isotope ratio analysis of sulfur in biological samples using inductively coupled plasma-mass spectrometry (ICP-MS) has gained significant interest for applications in quantitative proteomics. Advancements like coupling separation techniques with multicollector ICP-MS (MC-ICP-MS) enhance the throughput of species-specific sulfur isotope ratio measurements, fostering new avenues for studying sulfur metabolism in complex biological matrices. This proof-of-concept study investigates the feasibility of online CE/MC-ICP-MS for directly analyzing sulfur isotope ratios in proteins (albumin). Leveraging our previous work on the applicability of CE/ICP-MS for quantifying sulfur-containing biological molecules, we explore its potential for sulfur isotope analysis. Our results demonstrate that direct analysis of sulfur isotopes in albumin protein using online capillary electrophoresis MC-ICP-MS (CE/MC-ICP-MS) eliminates the need for laborious pretreatment steps, while yielding isotope ratios comparable to the reference values. Although initial precision can be improved through further system optimization and protein injection techniques, this approach paves the way for future analysis of mixtures of various biological compounds in, for example, clinical diagnosis studies.

Isotopic Composition of C, N, and S as an Indicator of Endometrial Cancer.

The metabolic pathway of cancerous tissue differs from healthy tissue, leading to the unique isotopic composition of stable isotopes at their natural abundance. We have studied if these changes can be developed into diagnostic or prognostic tools in the case of endometrial cancer. Measurements of stable isotope ratios were performed using isotope ratio mass spectrometry for nitrogen, carbon, and sulfur isotopic assessment. Uterine tissue and serum samples were collected from patients and the control group. At a natural abundance, the isotopic compositions of all three of the studied elements of uterus cancerous and healthy tissues are different. However, no correlation of the isotopic composition of the tissues with that of serum was found. Differences in the isotopic composition of the tissues might be a potential prognostic tool. However, the lack of a correlation between the differences in the isotopic composition of the tissues and serum seems to exclude their application as diagnostic biomarkers, which, however, might be possible if a position-specific isotopic analysis is performed.

An East Antarctic, sub-annual resolution water isotope record from the Mount Brown South Ice core

We report high resolution measurements of the stable water isotope ratios (δ18O, δD) from the Mount Brown South ice core (MBS, 69.11° S 86.31° E). The record covers the period 873 - 2009 CE with sub-annual temporal resolution. Preliminary analyses of surface cores have shown the Mount Brown South site has relatively high annual snowfall accumulation (0.3 metres ice equivalent) with a seasonal bias toward lower snowfall during austral summer. Precipitation at the site is frequently related to intense, short term synoptic scale events from the mid-latitudes of the southern Indian Ocean. Higher snowfall regimes are associated with easterly winds, while lower snowfall regimes are associated with south-easterly winds. Isotope ratios are measured with Infra-Red Cavity Ring Down Spectroscopy, calibrated on the VSMOW/SLAP scale and reported on the MBS2023 time scale interpolated accordingly. We provide estimates for measurement precision and internal accuracy for δ18O and δD.

Precise Determination of Cd Isotope Ratios at 3-10 ng Level by Thermal Ionization Mass Spectrometry Using a Molybdenum Silicide Emitter.

Thermal ionization mass spectrometry (TIMS) combined with the double spike technique has excellent analytical precision for Cd isotopic ratio analysis. However, because of the low ionization efficiency of Cd by TIMS, it is still not possible to obtain high precision Cd isotope ratios for small sample size (<100 ng) due to the lack of a highly sensitive emitter for Cd. A new loading method using molybdenum silicide (MoSi2) emitter has been developed for Cd isotope ratio measurements. This emitter produces a significant enhancement in the ionization efficiency of Cd and thus significantly reduces the required sample size to the 3-10 ng level. Analyses of δ114/110Cd for the NIST SRM 3108 using 108Cd-116Cd double spike method show excellent reproducibility (2 SD) that reaches ±0.032‰, ±0.042‰, and ±0.051‰ for 10, 5, and 3 ng of Cd, respectively. This method was further verified with a suite of geological reference materials. Replicate digestions and analyses (n = 8, 2 SD) of δ114/110Cd for NIST SRM 2711a, NOD A-1, and GBW08401 demonstrated good external reproducibility with results of 0.596 ± 0.024‰ for NIST SRM 2711a, 0.150 ± 0.036‰ for NOD A-1, and -0.665 ± 0.084‰ for GBW08401. These data clearly indicate that MoSi2 is an excellent alternative for traditional silica gel to Cd isotopic measurements, especially for samples with a low content of Cd.

Hydrogen isotope fractionation in plants with C3, C4, and CAM CO2 fixation.

Measurements of stable isotope ratios in organic compounds are widely used tools for plant ecophysiological studies. However, the complexity of the processes involved in shaping hydrogen isotope values (δ2H) in plant carbohydrates has limited its broader application. To investigate the underlying biochemical processes responsible for 2H fractionation among water, sugars, and cellulose in leaves, we studied the three main CO2 fixation pathways (C3, C4, and CAM) and their response to changes in temperature and vapor pressure deficit (VPD). We show significant differences in autotrophic 2H fractionation (εA) from water to sugar among the pathways and their response to changes in air temperature and VPD. The strong 2H depleting εA in C3 plants is likely driven by the photosynthetic H+ production within the thylakoids, a reaction that is spatially separated in C4 and strongly reduced in CAM plants, leading to the absence of 2H depletion in the latter two types. By contrast, we found that the heterotrophic 2H-fractionation (εH) from sugar to cellulose was very similar among the three pathways and is likely driven by the plant's metabolism, rather than by isotopic exchange with leaf water. Our study offers new insights into the biochemical drivers of 2H fractionation in plant carbohydrates.

Precise and accurate Ga isotope ratio measurements of geological samples by multi-collector inductively coupled plasma mass spectrometry

Precise and accurate Ga isotope ratio measurements of geological samples by multi-collector inductively coupled plasma mass spectrometry

Technical note: Optimizing the in situ cosmogenic 36Cl extraction and measurement workflow for geologic applications

Abstract. In situ cosmogenic 36Cl analysis by accelerator mass spectrometry (AMS) is routinely employed to date Quaternary surfaces and assess rates of landscape evolution. However, standard laboratory preparation procedures for 36Cl dating require the addition of large amounts of isotopically enriched chlorine spike solution; these solutions are expensive and increasingly difficult to acquire from commercial sources. In addition, the typical workflow for 36Cl dating involves measuring both 35Cl/37Cl and 36Cl/Cl concurrently on the high-energy (post-accelerator) end of the AMS system, but 35Cl/37Cl determinations using this technique can be complicated by isotope fractionation and system memory during measurement. The traditional workflow also does not provide 36Cl extraction laboratories with the data needed to calculate native Cl concentrations in advance of 36Cl/Cl measurements. In light of these concerns, we present an improved workflow for extracting and measuring chlorine in geologic materials. Our initial step is to characterize 35Cl/37Cl on sample aliquots of up to ∼1 g prepared in Ag(Cl, Br) matrices, which greatly reduces the amount of isotopically enriched spike solution required to measure native Cl content in each sample. To avoid potential issues with isotope fractionation through the accelerator, 35Cl/37Cl is measured on the low-energy, pre-accelerator end of the AMS line. Then, for 36Cl/Cl measurements, we extract Cl as AgCl or Ag(Cl, Br) in analytical batches with a consistent total Cl load across all samples; this step is intended to minimize source memory effects during 36Cl/Cl measurements and allows the preparation of AMS standards that are customized to match known Cl contents in the samples. To assess the efficacy of this extraction and measurement workflow, we compare chlorine isotope ratio measurements on seven geologic samples prepared using standard procedures and the updated workflow. Measurements of 35Cl/37Cl and 36Cl/Cl are consistent between the two workflows, and 35Cl/37Cl values measured using our methods have considerably higher precision than those measured following standard protocols. The chemical preparation and measurement workflow presented here (1) reduces the amount of isotopically enriched chlorine spike used per rock sample by up to 95 %; (2) identifies rocks with high native Cl concentrations, which may be lower priority for 36Cl surface exposure dating, at an early stage of analysis; and (3) allows laboratory users to maintain control over the total chlorine content within and across analytical batches. These methods can be incorporated into existing laboratory and AMS protocols for 36Cl analyses and will increase the accessibility of 36Cl dating for geologic applications.

Simultaneous Bulk‐Rock Elemental and Boron Isotope Ratio Measurement Using LA‐ICP‐MS on Silicate Micro‐Particulate Pellets

We have established a method for the simultaneous measurement of element abundances and boron isotopic compositions of bulk‐rock silicate samples by laser ablation coupled to two different ICP‐MS instruments. Fifteen silicate reference materials were prepared as micro‐particulate pressed powder pellets (MP) for analysis. Approximately 1/5th of the ablated material was transported to a single‐collector ICP‐MS for elemental measurement, while 4/5ths were sent to a multi‐collector ICP‐MS for boron isotope ratio measurement. Compositions of different milling materials (agate, zirconium oxide, tungsten carbide, sintered corundum and silicon nitride) were measured for the evaluation of potential contamination during sample preparation. Determined element mass fractions are in agreement with literature values within ±20%. For boron isotope ratios, the matrix‐dependent background elevation across the m/z from 9.9 to 11, and the effect of ablation mass was quantified. Measured δ11B values of most reference materials are consistent with literature values within ±1‰. The intermediate measurement precision is ±0.3‰ for JB‐2 with 30 μg g−1 B and ±0.4‰ for JA‐2 with 21 μg g−1 B. A publically available, web‐based streamlit app was developed for data processing (https://zenodo.org/doi/10.5281/zenodo.11150471). This paves the way for combined, accurate and precise elemental and boron isotope ratio measurements of geological materials.

An Analytical Method for Quantification of Sn Isotope Variations in Geological Materials Using MC‐ICP‐MS

A robust analytical method is presented here, for measurements of Sn isotope variations with high precision using a multi‐collector inductively coupled plasma‐mass spectrometer (MC‐ICP‐MS). A silicate rock dissolution procedure was used, together with means to remove organic matter introduced by the resin during ion‐exchange chromatography. The two‐stage ion exchange chromatography efficiently isolates Sn from the matrix and isobarically interfering elements, from samples with variable Sn mass fractions (~ 0.03 to 7 μg g−1). A double spike technique was also implemented to correct any secondary mass bias induced during sample processing and isotope ratio measurements. An intermediate precision (2s) of ± 0.47 was obtained for ε122/118Sn (using internal normalisation; n = 70 over a period of 29 months), ± 0.021‰ for δ122/118Sn (using double spike; n = 176 over a period of 29 months) and ± 0.059‰ for δ122/118Sn (using Sb doping; n = 34 over a period of 4.5 months) for the Sn standard solution, NIST SRM 3161a (Lot# 140917). The δ122/118SnNIST SRM 3161a of eleven geological reference materials are reported for the first time (BIR‐1a, BRP‐1, DTS‐2b, ECRM 782‐1, JP‐1, OKUM, QLO‐1a, RGM‐2, SGR‐1b, STM‐2 and UB‐N), with five others (AGV‐2, BCR‐2, BHVO‐2, GSP‐2 and W‐2a) showing similar results to previous studies, generally with improved precision. The intermediate precision (2s) of replicate dissolutions of ten RMs (AGV‐2, BCR‐2, BHVO‐2, BIR‐1a, DTS‐2b, GSP‐2, OKUM, SGR‐1b, STM‐2 and W‐2a) varied from 0.003 to 0.054‰. Typical repeatability precision (2SE) of individual measurements of these ten RMs over multiple measurement sessions varied from 0.031 to 0.297‰ (with 120Sn+ beam intensity &lt; 2.37 V) and 0.017 to 0.025‰ (with 120Sn+ beam intensity &gt; 2.37 V).

Quantifying particulate organic matter: source composition and fluxes at the river-estuary interface

Particulate organic matter (POM) characteristics and variability have been widely studied along the land-ocean aquatic continuum, yet, gaps remain in quantifying its source composition, fluxes, and dynamics at the river-estuary interface. POM in rivers consists of a complex mixture of sources, derived both from locally produced (i.e. phytoplankton) and from adjacent ecosystems (e.g. terrestrial POM). Each source differ in its trophic and biogeochemical characteristics, hence impacting its integration into local food webs, its transfer to estuaries and sea, and its contribution to biogeochemical processes. In this study, we use a robust approach based on in situ POM to characterize river POM end-members, to quantify POM composition and dynamics, and to identify the related key drivers. This study was performed at the River-Estuary interface of one of the main rivers in Western Europe (the Loire River, France). For 3 years, we conducted bimonthly measurements of carbon and nitrogen isotopic (δ13C, δ15N) and elemental (C/N) ratios to quantify the contribution of two sources (phytoplankton and terrestrial POM) to the POM mixture and calculated annual fluxes of particulate organic carbon (POC) and nitrogen (PN) sources. Throughout the year, POM consisted of ~65% phytoplankton and 35% terrestrial POM. The mean annual export fluxes were 40.6 tPOC/year and 2.45 tPN/year over the studied period, with half of it originating from phytoplankton (53 and 55% for POC and PN, respectively). We observed a clear seasonal pattern in POM composition: phytoplankton predominated from March to October, in relation to high primary production, while terrestrial contributions were the highest from November to February, driven by greater autumn-winter hydrodynamics. Our study illustrate the interest of such an approach to quantify POM composition in aquatic system and estimate source fluxes, and provide fundamental results for estimating seasonal baselines in food webs, establishing biogeochemical budgets, and quantifying POM exports to estuarine and marine environments. Applying this methodology across a broad spectrum of aquatic systems should enhance our understanding of biogeochemical processes and organic matter transformation along the land-ocean continuum and illustrates the contribution of these ecosystems to global biogeochemical cycles.

Accuracy Improvement in the LA‐MC‐ICP‐MS Measurement of 87Sr/86Sr in Bioapatite Using Dentin of Carcharinus leucas (Bull shark) to Estimate 87Rb/85Rb Instrument Induced Fractionation

In situ 87Sr/86Sr microanalysis in bioapatite using laser ablation (LA‐)MC‐ICP‐MS is an essential tool for provenance studies, as enamel tissue build‐up records the regional Sr isotopic composition of ingested food and water sources. Several factors hamper the acquisition of reliable and precise 87Sr/86Sr data: isobaric interferences, elemental and isotopic fractionation of Rb and Sr, and the lack of certified reference materials. Here we thoroughly characterise several teeth from Carcharinus leucas (Bull shark) for the spatial distribution of Sr and Rb mass fraction by LA‐ICP‐Q‐MS, and their 87Sr/86Sr ratio by solution MC‐ICP‐MS, MC‐TIMS and LA‐MC‐ICP‐MS, and which were used subsequently as a reference material during laser ablation measurement of Sr isotope ratios in bioapatite. We establish a protocol to estimate the 85Rb/87Rb mass bias from the analysis of shark teeth that demonstrates that the common assumption of equal Sr and Rb instrument induced fractionation can lead to a systematic bias in 87Sr/86Sr isotope ratios. Using the shark teeth as an "external" reference material to measure βRb yielded 87Sr/86Sr compositions in unknown samples that are within approximately ‐42 ppm to +66 ppm of expected values, instead of approximately ‐50 ppm to +190 ppm if assuming βRb = βSr. Finally, this methodology was tested on fossil gomphotherid (Rhynchotherium sp.) enamel, allowing us to make preliminary inferences about its palaeobiogeography.

High‐Resolution In Situ Fe Isotope Measurements of Silicate Minerals and Glasses by Femtosecond Laser Ablation MC‐ICP‐MS

In this study, we present a high precision and high spatial resolution in situ Fe isotope protocol using femtosecond (fs) laser ablation multi‐collector inductively coupled plasma‐mass spectrometry (LA‐MC‐ICP‐MS). The intermediate measurement precision obtained over a period of ca. 3 years for the USGS glass BIR‐1G against the Puratronic reference material is 0.17‰ (2s) for δ56Fe. Uncertainties achieved on individual analyses of glass and olivines were &lt; 0.15‰ for δ56Fe. This high precision is associated with high spatial resolution of about 170 × 25 μm. Our results display good consistency between LA‐MC‐ICP‐MS and solution nebulisation MC‐ICP‐MS data from the literature. Obtained δ56Fe values on different USGS glasses (BIR‐1G, BHVO‐2G and BCR‐2G) show that these reference materials have homogenous Fe isotope ratio and therefore can be used as bracketing calibrators during laser ablation measurement sessions. On the other hand, the San Carlos Olivine displays high Fe isotope heterogeneity, and therefore cannot be considered as a good bracketing standard (calibrator). We also applied our fs‐LA‐MC‐ICP‐MS protocol to olivines and pyroxene from the Kerguelen Archipelago. This technique appears to be a relevant tool to resolve isotopic zoning in chemically zoned silicate phenocrysts, even of small size (&lt; 1 mm). We demonstrate that within single lavas, olivine crystals display various zoning depending on their size, related to their residence time in the magma. Both equilibrium and diffusive processes were observed in olivine crystals from Kerguelen, uncovering complex histories. Hence, iron isotope ratio measurements by fs‐LA‐MC‐ICP‐MS open new possibilities for studying highly zoned silicate minerals in magmatic rocks to better understand their formation.

Towards Improved Measurement of Chemical Composition and Isotope Ratios of Rare-earth Phosphates in Atom Probe Tomography

Towards Improved Measurement of Chemical Composition and Isotope Ratios of Rare-earth Phosphates in Atom Probe Tomography

Sample preservation methods for nitrous oxide concentration and isotope ratio measurements in aquatic environments

AbstractThe nitrogen (N) and oxygen (O) stable isotope analysis of dissolved nitrous oxide (N2O) can provide important constraints on the sources and cycling of N2O in aquatic environments. The isotopic composition of aqueous N2O, both in field (natural abundance) or experimental (15N‐labeling) samples, however, may be altered by abiotic reactions involving nitrite () or hydroxylamine (NH2OH) and microbial activity during sample storage, if samples are not adequately preserved. Here we tested five different preservatives, mercuric chloride (HgCl2), copper sulfate (CuSO4), zinc chloride (ZnCl2), hydrochloric acid (HCl) mixed with sulfamic acid (SFA), and sodium hydroxide (NaOH), for fixing natural water samples from an estuary and a lake with different concentrations over a range of different storage times for N2O analyses. ZnCl2 and CuSO4 decreased the pH, and led to abiotic N2O production from , shifting the N2O isotopic composition significantly. Removal of with a mixture of SFA and HCl did not always prevent the alteration of the original N and O isotope composition of N2O, confirming the requirement for complete removal, and underscoring the biasing effects of at very low pH, even at trace levels. At low background, HgCl2 preservation led to robust and accurate results. However, in light of its toxicity and bioaccumulation potential in food webs, this fixative should be avoided. The addition of NaOH reduced abiotic side reactions involving , and yielded the most reliable and reproducible results for N2O concentration and isotope ratio measurements across tested settings and storage times.

Developing δ15N and δ13C isoscapes using whole blood from Magellanic penguins, Spheniscus magellanicus.

Understanding the migration of marine animals is hindered by the limitations of traditional tracking methods. It is therefore crucial to develop alternative methods. Stable isotope-based tracking has proven useful for this task, although it requires detailed isoscapes in the focal area. Here, we present predator-based isoscapes of the coastal zone of the Patagonian Shelf Large Marine Ecosystem (PSLME), which offers a novel tool for geolocation. Whole-blood samples from breeding Magellanic penguins nesting at 11 colonies were used to create δ15N and δ13C isoscapes. Isotopic values were assigned to random positions inside their corresponding foraging area. Spatial analysis and data interpolation resulted in δ15N and δ13C isoscapes for the coastal zone of the PSLME, which were validated through cross-validation. The isoscapes mean standard error ranged from 0.05 to 0.41 for δ15N and from 0.07 to 0.3 for δ13C, similar to the error range of the mass spectrometer used for measuring isotope ratios. Predictive surfaces reflected the latitudinal trends, with δ13C and δ15N values increasing northwards. δ13C values showed a strong latitudinal gradient, while δ15N values had two distinct domains, with higher values in the north. The error surface indicated the highest certainty within 130 km from the shore and within the reported Magellanic penguin foraging areas. Both isoscapes revealed strong spatial variation. The δ13C isoscape showed a latitudinal gradient, consistent with patterns in other oceans. The δ15N isoscape clearly separated northern and southern colonies, likely influenced by nitrogen sources. The error obtained fell within the measurement error ranges, adding credibility to the models.

Zinc isotope fractionation during coprecipitation with amorphous iron (hydr)oxides

Coprecipitation facilitates the incorporation of Zn into the lattice of Fe (hydr)oxide, which is a crucial mechanism causing low Zn bioavailability in widespread Zn-deficient soils. Zn isotopes are a potential indicator of the coprecipitation of Zn and Fe (hydr)oxides in soils. However, the Zn isotope fractionation caused by coprecipitation with amorphous Fe (hydr)oxides (e.g., ferrihydrite) and the impact of environmentally relevant conditions remain unknown. Here, the molecular mechanism and impact factor of Zn isotope fractionation during Zn2+-Fe3+ coprecipitation under natural soil conditions (including different pH values and initial Zn/Fe ratios) were investigated by combining isotope ratio measurements, extended X-ray absorption fine structure (EXAFS) analyses, and density functional theory (DFT) geometry optimization. The results show that aqueous Zn (Znaq) can be complexed on the ferrihydrite surface (Znads) with positive isotope fractionation (Δ66Znads–aq = 0.42 ± 0.09 ‰) or directly incorporated into the ferrihydrite lattice with slightly negative isotope fractionation (Δ66Znstru-aq = −0.08 ± 0.03 ‰). In addition, over time, the surface-complexed Zn can further transform to a layered structure on the surface but exhibits limited Zn isotope fractionation. According to Zn K-edge EXAFS, the Zn isotope fractionation of surface complexation and incorporation of Znaq are related to the decrease in the Zn–O bond strength in the order surface complexed Zn (RZn–O = 2.00 Å) > aqueous Zn (RZn–O = 2.08 Å) > directly incorporated Zn (RZn–O = 2.06–2.07 Å with slight distortion). The limited Zn isotope fractionation associated with the transformation of Znads is related to the reconfiguration of Znads during the nucleation of octahedral Zn layer structures. Furthermore, the primary process controlling Zn isotope fractionation is different under varying experimental conditions, leading to distinct Zn isotope fractionation between the bulk solid and solution during Zn–Fe coprecipitation. Low pH values (5.0–6.0) and initial Zn/Fe ratios (0.01–0.02) favor the direct precipitation of Znaq, resulting in slightly negative Zn isotope fractionation between the bulk solid and solution. In contrast, high pH values (7.0–7.5) and initial Zn/Fe ratios (0.1–0.2) favor surface complexation and the transformation of Znads, leading to heavy Zn isotope enrichment in the bulk solid. These findings offer novel insights into the primary mechanism through which Fe (hydr)oxides regulate Zn bioavailability in Zn-deficient soils and provide experimental evidence supporting the potential application of Zn isotopes as an indicator for comprehending the fate of Zn controlled by Fe (hydr)oxides in soils.

Reliability Evaluation for Mercury Stable Isotope Ratio Measurement by MC-ICP/MS

This study assessed the reliability of Mercury (Hg) stable isotope ratio measurements using MC-ICP/MS hyphenated with three different systems: wet plasma, dry plasma, and a cold vapor generator (CVG). Precision measurements using wet plasma improved with concentration, showing a range of 0.4 - 10.0% at 100 µg/L, with corresponding accuracy from 0.0 – 0.4%. By contrast, dry plasma demonstrated precision between 0.02 - 2.2% at 10 µg/L for 202/198Hg, with accuracy ranging from 1.2 - 1.4%. The CVG system, however, displayed significantly enhanced accuracy, from 0.2% for 199/198Hg to 0.9% for 204/198Hg at 0.1 µg/L. The study also incorporated a mass bias correction using a thallium (NIST 997 standard) internal spike, emphasizing the importance of maintaining a total Hg beam above 0.5 V to ensure measurement precision and accuracy. The findings suggest that the CVG method is most suitable for environmental samples with trace Hg concentrations, while both dry and wet plasma systems can serve effectively at higher concentrations (≥ 100 µg/L), given their analytical convenience and performance.

Exploration of metallic interferences pertinent to nuclear safeguards related uranium isotope ratio measurement on the Neoma MC-ICP-MS platform without the MS/MS option

In this paper we present basic observations regarding the formation and effect of various polyatomic metallic interferences (combinations of Pb, Al, Si, Mo, W, Fe, Sn, Ti, Ba, and Pt) on uranium isotopic ratios measured via a new Multi Collector – Inductively Coupled Plasma – Mass Spectrometer (MC-ICP-MS) platform: The ThermoFisher Scientific™ Neoma® (without the MS/MS® collision cell option). Our approach is to dope a uranium isotopic standard (IRMM-2020) with various quantities of the metallic elements, all of which have been previously identified as posing isobaric interferences during uranium isotope measurement, and then perform analyses in solution mode and by laser ablation (LA) MC-ICP-MS. As expected, there is considerable variability between the different elementally doped solution and the degree of perturbation exhibited by the uranium isotope standard. However, Pt appears to induce the most drastic shift for 234U/238U, 235U/238U, and 236U/238U. One unexpected result is that the presence of Pb, whether alone or in combination with Al and Si, appears to result in a reduction of the expected uranium signal. This effect was observed (and re-confirmed using a different cup configuration) on the Neoma® MC-ICP-MS during wet plasma analysis, but was not observed during dry plasma conditions (e.g. laser ablation sampling of dried IRMM-2020 containing Pb). Furthermore, the phenomenon was also not observed during dry plasma analysis on a NeptunePlus®. Further experiments will be necessary to fully understand the origin of this signal attenuation, and the results of our study highlight the need for continued investigation of the polyatomic interference issue as new MC-ICP-MS platforms are developed since our results clearly demonstrate that they can drastically skew the observed isotope ratios in sometimes unexpected directions. Lastly, the use of N2 during LA sampling appears to slightly increase the magnitude of the interferences compared to when only Ar is utilized as the carrier gas. This observation further highlights the importance of plasma conditions on interference formation.

A preliminary investigation into the feasibility of laser ablation U-Pb isotope ratio measurement via all-faraday cup detection with 1011- and 1013-Ω amplifiers on the Neoma multicollector-inductively coupled plasma-mass spectrometer.

Signal detection for uranium-lead (U-Pb) dating of zircon is typically performed via ion counters. Here, we develop a preliminary understanding of the strengths and limitations of faraday-cup-based detection. A suite of zircon reference materials and the NIST-610 glass were sampled using laser ablation followed by U-Pb isotope ratio measurement on a Neoma multicollector-inductively coupled plasma-mass spectrometer. We were able to produce geologically accurate 207Pb/206Pb, 206Pb/238U, and 207Pb/235U ratios for the NIST-610 glass and the zircon standards, with ages ranging from ~2.5Ga to ~337 Ma (TanBrown A, Oracle, 91550, Mud Tank, Temora, and Plešovice). Two of the younger zircon standards examined (94-35, ~55.6Ma, and Fish Canyon, 28.6Ma) yielded accurate 206Pb/238U but not 207Pb/235U or 207Pb/206Pb ratios, whereas the youngest zircon standard (Penglai, ~4.4Ma) failed for all three ratios of interest. The accuracy and precision of the all-faraday method are directly tied to signal intensity, with reliable data capable of being produced even when both isotopes in a ratio have signals below ~0.001 V (equivalent to ~62 500 cps on an ion counter). The all-faraday cup multicollection method provides sufficient sensitivity to obtain geologically meaningful U-Pb data, with possible advantages being that laser pit depth-dependent changes in the observed interelemental fractionation behavior may be easier to correct using a static collector configuration compared to when the ion beam is swept across a single detector while also removing the need for an interdetector-type calibration. Further work is needed to refine the all-faraday cup method (e.g., application of background subtraction and common Pb corrections, outlier removal, and interelement as well as down-hole fractionation corrections), but our initial results demonstrate that the faraday detector method has sufficient sensitivity to warrant further study.