Multi-collector Inductively Coupled Plasma Mass Spectrometry Research Articles

Determination of the isotopic composition of tungsten using MC-ICP-MS

The processes of planetary accretion or formation of the Earth and other celestial objects can be studied by using the 182Hf-182W chronometer which requires precise measurements of tungsten isotope ratios. Many comparative measurements for the isotopic composition of tungsten have been performed using either thermal ionization mass spectrometry (TIMS) or multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS). Yet, calibrated measurements of tungsten isotope ratios, and, in turn, isotopic abundances and atomic weight, are still lacking. In this study, we report the first independent measurements of all tungsten isotope ratios in five commercial tungsten reagents, including the new NRC candidate isotopic reference material WOLF-1 by MC-ICP-MS with use of the-state-of-the-art optimized regression mass bias correction model and NIST SRM 989 isotopic rhenium as calibrator.

Determination of the isotopic composition of hafnium using MC-ICPMS

Despite the numerous important applications of hafnium isotopes in geological science, and the advances in multi-collector inductively coupled plasma mass spectrometry (MC-ICPMS), hafnium still lacks calibrated measurements of its isotope ratios and, in turn, isotopic abundances and atomic weight. In this study, we determined the isotopic composition of hafnium in four commercial hafnium reagents, including a commonly used hafnium standard (JMC-475) and a NRC candidate isotopic reference material (HALF-1) by MC-ICPMS. The state-of-the-art regression model with NIST SRM 989 isotopic rhenium as calibrator was used to correct instrumental isotopic fractionation without reliance on other hafnium standards, normalizing isotope ratios, or exponential mass-bias fractionation model.

Anion-Specific Sulfur Isotope Analysis by Liquid Chromatography Coupled to Multicollector ICPMS.

An accurate method has been developed to measure, in a single analytical run, δ34S in sulfite, sulfate and thiosulfate in water samples by liquid chromatography combined with multicollector inductively coupled plasma mass spectrometry (MC-ICPMS). The method is based on the anionic exchange separation of sulfur species prior to their online isotope ratio determination by MC-ICPMS. Mass bias correction was accomplished by a novel approach based on the addition of an internal sulfur-containing standard to the sample. This innovative approach was compared to the sample-standard bracketing procedure. On-column isotopic fractionation was observed and therefore corrected by external calibration. Isotopic ratios were calculated by linear regression slope (LRS), an advantageous method for transient signals, leading to a combined uncertainty of δ34S below 0.25‰ and a reproducibility below 0.5‰ for the injection of 1 μg of S. The method was successfully applied to the measurement of δ34S in synthetic solutions and environmental water samples. Matrix effects leading to δ34S overestimation were observed for sulfate in some samples with high sodium/sulfate mass ratios. The developed analytical procedure simplifies the δ34S analysis of liquid environmental samples since preparation steps are no longer required and allows the analysis of several sulfur-containing species in a single run.

Production and characterization of 60Fe standards for accelerator mass spectrometry.

Accelerator Mass Spectrometry (AMS) is one of the most sensitive analysis techniques to measure long-lived radionuclides, reaching detection limits for isotopic ratios down to 10−15–10−16 in special cases. Its application portfolio covers nearly every field of environmental research, considering processes in the atmosphere, biosphere, hydrosphere, cryosphere, lithosphere and the cosmosphere. Normally, AMS measures the content of isotopes in comparison to a validated standard. However, in some cases like for example 60Fe, well characterized standard materials are difficult to produce due to the extreme rareness of the isotope. We report here on the manufacturing of a set of 60Fe standards, obtained by processing irradiated copper from a beam dump of the high-power proton accelerator (HIPA) at the Paul Scherrer Institute (PSI). The isotopic ratios of the standards have been adjusted via a dilution series of a master solution, isotopic content of which has been characterized by Multi Collector–Inductively Coupled Plasma–Mass Spectrometry (MC-ICP-MS). In total, we produced three samples with isotopic ratios of 1.037(6)·10−8, 1.125(7)·10−10 and 1.234 (7)·10-12, respectively. The latter had already been applied in three pioneering AMS studies investigating the remaining signal of injected matter of nearby super novae explosions in sediment archives.

Fast and precise boron isotopic analysis of carbonates and seawater using Nu Plasma II multi-collector inductively coupled plasma mass spectrometry and a simple sample introduction system.

The boron (B) isotopic composition in marine carbonates provides important insights into paleoclimate reconstruction and biomineralization. However, precise and accurate measurements of B isotopes using plasma-based mass spectrometry is difficult due to the volatile nature of B, which typically requires complex and more specialized sample introduction systems. Existing analytical protocols have mostly been based on Thermo Scientific Neptune Plus multi-collector inductively coupled plasma mass spectrometry (MC-ICPMS) instruments, whereas methods based on Nu Plasma mass spectrometers are scarce. We have developed a simplified analytical protocol using Nu Plasma II MC-ICPMS with standard glass sample introduction systems. Boron extraction and purification were conducted using a two-stage column chemistry with cation-exchange and Amberlite IRA 743 B-specific resin. A sample drying step was avoided, which allows for direct isotopic analysis after column chemistry. A wet plasma mode with a standard glass cyclonic spray chamber and a glass nebulizer was used instead of a more specialized perfluoroalkoxy (PFA) sample introduction system. Low residual B signals were achieved with a relatively short period of wash-out with 0.5 N HNO3 . The external precision is better than 0.30‰ (2SD) calculated from the long-term bracketing standard, NIST SRM 951a. The overall robustness of the method was demonstrated by measurements of the international carbonate standard JCp-1 (δ11 B = +24.49 ± 0.36‰, 2SD) and seawater (δ11 B = +39.98 ± 0.35‰), which are consistent with reported values. Our method provides an alternative approach for B isotope analysis using a routine wet plasma MC-ICPMS setup that can facilitate geochemical and environmental application of B isotopes.

Boron isotope variability related to boron speciation (change during uptake and transport) in bell pepper plants and SI traceable n(11 B)/n(10 B) ratios for plant reference materials.

Boron (B) is an essential micronutrient in plants and its isotope variations are used to gain insights into plant metabolism, which is important for crop plant cultivation. B isotope variations were used to trace intra-plant fractionation mechanisms in response to the B concentration in the irrigation water spanning the range from B depletion to toxic levels. A fully validated analytical procedure based on multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS), sample decomposition and B matrix separation was applied to study B isotope fractionation. The validation was accomplished by establishing a complete uncertainty budget and by applying reference materials, yielding expanded measurement uncertainties of 0.8‰ for pure boric acid solutions and ≤1.5‰ for processed samples. With this validated procedure SI traceable B isotope amount ratios were determined in plant reference materials for the first time. The B isotope compositions of irrigation water and bell pepper samples suggest passive diffusion of the heavy 11 B isotope into the roots during low to high B concentrations while uptake of the light 10 B isotope was promoted during B depletion, probably by active processes. A systematic enrichment of the heavy 11 B isotope in higher located plant parts was observed (average Δ11 Bleaf-roots = 20.3 ± 2.8‰ (1 SD)), possibly by a facilitated transport of the heavy 11 B isotope to growing meristems by B transporters. The B isotopes can be used to identify plant metabolism in response to the B concentration in the irrigation water and during intra-plant B transfer. The large B isotope fractionation within the plants demonstrates the importance of biological B cycling for the global B cycle.

Lead isotope and geochemical analyses of copper-based metal artefacts from the Iron Age water burial in Levänluhta, Western Finland

This article presents the results of the first-ever lead isotope (LI) analysis of copper-based archaeological artefacts found in the region of Finland. Eight metal objects recovered from the Iron Age water burial site of Levänluhta in western Finland were analysed via multi collector inductively coupled plasma mass spectrometry (MC-ICP-MS) and portable X-ray fluorescence spectrometry (pXRF) in order to attain geochemical and LI data. The majority of the objects are Merovingian period (ca. 550–800 CE) jewellery, displaying domestic Iron Age artefact styles, and were probably cast by local workshops in Finland. Until recently, the copper exploited in Bronze and Iron Age metallurgy in Finland had been linked to Scandinavian ores. However, this provenance scenario seems implausible in the light of recent LI studies demonstrating that Scandinavian Bronze Age artisans in fact relied on long-distance metal transport. Comparisons between the LI data of the analysed objects and published ore databases exclude the possibility of a domestic or Scandinavian copper source for the metals. Instead, it appears likely that the copper originated from southern European ores. The low arsenic and antimony levels in the copper alloys provide indication of long recycling patterns of the metals used in the Iron Age workshops in Finland. It is possible that the Iron Age artefacts contain recycled copper-alloys already acquired in the Bronze Age. The metals were transported for long distances, and it appears that the pan-European metal circulation network also crossed the Baltic Sea to reach coastal Finland.

Separation of Uranium and Thorium for 230Th-U Dating of Submarine Hydrothermal Sulfides.

The age of a submarine hydrothermal sulfide is a significant index for estimating the size of hydrothermal ore deposits. Uranium and thorium isotopes in the samples can be separated for 230Th-U dating. This article presents a method to purify and separate U and Th isotopes in submarine hydrothermal sulfide samples. Following this technique, the separated U and Th fractions can meet measuring requirements by multi-collector inductively coupled plasma mass spectrometry (MC-ICPMS). The age of the hydrothermal sulfide sample can be calculated by measuring the present-day activity ratios of 230Th/238U and 234U/238U. A super clean room is necessary for this experiment. Cleaned regents and supplies are used to reduce the contamination during the sample processes. Balance, hotplate, and centrifuge are also used. The sulfide sample is powdered for analysis and less than 0.2 g sample is used. Briefly, the sample is weighed, dissolved, added to 229Th-233U-236U double spike solution, Fe co-precipitated, and separated on an anion-exchange resin extraction column. Approximately 50 ng U is consumed for 230Th-U dating of sulfides sample by MC-ICPMS.

Cellular and sub-cellular Cu isotope fractionation in the human neuroblastoma SH-SY5Y cell line: proliferating versus neuron-like cells.

Cu isotope fractionation was investigated in the human neuroblastoma SH-SY5Y cell line, in a proliferating/tumor phase (undifferentiated cells), and in a differentiated state (neuron-like cells), induced using retinoic acid (RA). The SH-SY5Y cell line displays genetic aberrations due to its cancerous origin, but differentiation drives the cell line towards phenotypes suitable for the research of neurological diseases (e.g., Alzheimer's disease or Parkinson's disease). Cellular Cu distribution was first explored by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) imaging and, subsequently, Cu isotopic analysis was performed at cellular and sub-cellular levels via multi-collector inductively coupled plasma-mass spectrometry (MC-ICP-MS). The SH-SY5Y cells showed a re-distribution of intracellular Cu upon RA differentiation. Both undifferentiated and differentiated cells became systematically enriched in the light 63Cu isotope with increasing intracellular Cu content. Differentiated neuron-like SH-SY5Y cells showed a heavier Cu isotopic composition (+ 0.3‰) than did the undifferentiated proliferating cells when exposed to Cu for 24h. However, after a longer exposure time (72h), no difference was observed between both cellular phenotypes. Mitochondrial fractions were enriched in the light 63Cu isotope, compared to whole cells, for both undifferentiated and differentiated cells (no significant difference). The Cu isotopic composition of the remaining cell lysates was heavier than that of the whole cells and + 0.2‰ heavier in the differentiated cells than in the undifferentiated cells. These results indicate that neuronal differentiation affects the Cu isotope fractionation accompanying Cu uptake in the cells, but this effect does not seem to be associated with the mitochondrial Cu pathway. Cu isotope fractionation can be an interesting tool for studying Cu metabolism at a (sub)-cellular level in functional neurons. Graphical abstract.

Application of an Isotope Binary Mixing Model for Determination of Precise Mercury Isotopic Composition in Samples with Low Mercury Concentration.

An isotope binary mixing model was applied for high precision measurement of mercury isotope ratios in samples with low mercury concentrations by multicollector inductively coupled plasma mass spectrometry (MC-ICPMS). Standard addition was used to evaluate the precision and accuracy of the isotope composition calculations resulting from the isotope binary mixing model. A high, steady 202Hg signal of approximately 2.13 V was achieved, with the mercury concentration reaching 3 ng/mL. The isotopic composition of three standards (NIST SRM 1646a; NIST SRM 1575a; BCR 482) and natural samples were precisely determined. The standards and natural samples were diluted to low mercury concentrations (low to 0.90 ng/mL) and mixed with standard solutions (NIST SRM 3133) with high mercury concentrations (50 ng/mL); the isotopic compositions of low mercury concentration samples were calculated using an isotope binary mixing model after the isotopic compositions of the mixing solutions were measured. The results showed that the uncertainty of the calculated mercury isotopic compositions was in an acceptable range and the calculation isotope data were in good agreement with direct measurements. Our method allows the precise determination of mercury isotope composition in mercury solutions of concentrations (0.90 ng/mL) below the detection limit of the current system (3.00 ng/mL).

Accurate Determination of Lithium Isotopic Compositions in Geological Samples by Multi-collector Inductively Coupled Plasma-Mass Spectrometry

Abstract Accurate determination of lithium (Li)isotopic composition in natural geological samples is the basis for Li isotope geochemical studies. In this study, a method contained preparation of geological materials (water and rock) and accurate determination of Li isotopic composition was set up. The separation of Li from water and rock samples was implemented by a single column containing 1.5 mL of Bio-Rad AG 50W-X12 (200–400 mesh) resin, with 0.40 M HCl and 1.0 M HCl as eluents. Only 8.5 and 14 mL of eluents were used to separate Li from water and rock samples with this method, respectively. Blank signal of the operation procedure was (2.4 ± 0.1) mV, which was almost same as the 2.3 mV of the 2% HNO3 signal used in this study. Experimental results showed that Li isotopic fractionation during leaching process was significant and deviation of δ7Li values in these samples with incompletely recovered Li reached up to 50‰. Lithium isotopic ratios were determined by multi-collector ICP-MS (Nu Plasma II) using the sample standard bracketing (SSB) method. L-SVEC standard with similar Li concentration to samples (about 80 ng mL−1) was used in this study. The external precision (2σ) of this technique, determined by repeated measurement of pure Li standard solutions and seawater was

A simple method for Cu, Zn and Mo purification and mass bias correction for precise and accurate isotopic ratio determination in geological samples by MC-ICPMS

A simple and quick method for simultaneous purification of Cu, Zn and Mo and accurate and precise measurement of their isotopic composition in geological samples using multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) has been developed. The method involves the use of a single chromatographic column filled with the anion exchange resin AG-MP-1 for complex matrix removal and further purification of these three elements. The external standard-sample-standard bracketing (SSB) procedure combined to internal standard addition was used for accurate mass bias correction and precise Cu, Zn and Mo isotopic ratio measurements. The method was applied to different geological materials, as granodiorite (GSP 2-USGS), limestone (JLS-1, Japan), Buffalo River Sediments (NIST SRM - 8704) and sediments from Amazon River Basin. The mean precision for these samples was: 0.08 ‰ for δ65/63Cu; 0.05 ‰ for δ66/67Zn and 0.04 ‰ for δ98/95Mo. The main advantage is that the proposed method is simple and rapid, and carries out the quantitative recovery of elements of different atomic masses and at very low concentration ranges, mainly for Mo. In addition, optimizations made the calibration and correction of instrumental mass bias easier, leading to consistent results with other methods that are currently published. The comparison of isotopic compositions of Cu and Mo obtained for granodiorite with respect to data reported in the literature demonstrate that the simpler and multi-element method developed in this study can be properly used within the required limits of accuracy as a multi-proxy tool in isotope geochemistry.

Effects of cone combinations on accurate and precise Mg-isotopic determination using multi-collector inductively coupled plasma mass spectrometry.

High-precision determination of magnesium (Mg) isotopes can now be routinely achieved by multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS). The analytical sensitivity and instrumental mass discrimination behavior of this method are, however, sensitive to the types of sample and skimmer cones used in these measurements, so it is important that these parameters should be investigated. Using the sample-standard-bracketing method in the wet-plasma mode, four available combinations of sample and skimmer cones [Jet sample cone + H skimmer cone (Jet + H), standard sample cone + H skimmer cone (Standard + H), standard sample cone + X skimmer cone (Standard + X), and Jet sample cone + X skimmer cone (Jet + X)] were systematically investigated for peak shape, sensitivity, mass discrimination, accuracy, and precision in Mg-isotopic ratio determination using a Neptune plus MC-ICP mass spectrometer. The results showed that different cone combinations do not affect peak shapes but would significantly change the sensitivities for Mg-isotopic determinations. Compared with using the Standard + H, the sensitivities of Mg-isotopic determinations were enhanced by approximately a factor of 1.3, 1.4, and 1.9 by using the Standard + X, the Jet + H, and the Jet + X combinations, with the most stable mass discrimination behaviors obtained by the Jet + H. The instrumental mass fractionation slope for any combination of a modified cone geometry (i.e. Standard + X, Jet + X, and Jet + H) is 0.500, while it is 0.510 for the Standard + H. In addition, the mass discrimination behavior is related to Mg concentrations once the combination is set, indicating the necessity of concentration match during Mg-isotopic determination. The precision and accuracy of the Jet + H combination are better than those of the other combinations, and this is further supported by the validation of the Mg-isotope data for four international reference materials: Cambridge-1, NASS-6, AGV-2, and BHVO-2. As the Jet + H combination also provides a high signal, this combination gives the most robust strategy for the highly precise and accurate determination of Mg isotopes.

Quantitative Data Extraction from Orthopyroxene Trace Element Maps and Its Potential to Examine the Formation of the UG2 Unit, Bushveld Complex

We present a mineral chemical stratigraphy across the UG2 Unit, situated in the Upper Critical Zone of the Bushveld Complex. The magmatic evolution of the rocks hosting this world-class ore deposit for chromium and platinum group elements (PGEs) is still under debate. Orthopyroxene is a common phase across the magmatic stratigraphy of the unit. It hosts trace metals, whose relative contents can record information about magmatic processes. This study determined laser ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS) trace element data for orthopyroxene and spot LA multi-collector ICP-MS Sr-isotope data for plagioclase. Mapping of trace element distributions revealed internal zoning in Cr, V, Y, and Th. Unlike in conventional spot analysis, quantitative trace element concentrations were extracted post-analysis from two-dimensional LA-ICP-MS maps. This approach offered advantages over spot analysis. The maps revealed internal complexities (e.g., inclusions, exsolved phases, zonations and diffusion halos) that could be avoided with suitable thresholds for chemical filter elements (i.e., 100 ppm < Cr < 4000 ppm, Y < 6 ppm), permitting fast, automated extraction of pure orthopyroxene data pixels from elemental maps covering noritic, troctolitic, anorthositic and chromititic mineral assemblages. Diffusive equilibration in orthopyroxene was evaluated by comparing zonations in elements with different known diffusivities. Magnesium and Ni are homogenously distributed, indicative of rapid diffusive processes, while Cr and V show zonations, interpreted to largely reflect primary distribution. Thorium and Y apparently diffused along discrete pathways, indicated by concentration anomalies following orthopyroxene lamellae. A systematic study of the trace element inventory of orthopyroxene across the succession of the UG2 Unit, complemented with Sr isotope signatures of plagioclase, revealed clear evidence for open-system processes: compatible elements (Cr, Ni) are decoupled from Mg# variations in orthopyroxene from specific UG2 subunits; distinct Mg# peaks coincide with negative V excursions in orthopyroxene from chromite-bearing subunits; towards the top of the unit, plagioclase shows a distinct 87Sr/86Srinitial peak and orthopyroxene shows Cr-depleted and Th-enriched rims. These chemical features cannot be explained by crystal mixing alone and argue for the involvement of at least two chemically distinct melts in the formation of the studied UG2 section.

GHR1 Zircon – A New Eocene Natural Reference Material for Microbeam U‐Pb Geochronology and Hf Isotopic Analysis of Zircon

We present multitechnique U‐Pb geochronology and Hf isotopic data from zircon separated from rapakivi biotite granite within the Eocene Golden Horn batholith in Washington, USA. A weighted mean of twenty‐five Th‐corrected 206Pb/238U zircon dates produced at two independent laboratories using chemical abrasion‐isotope dilution‐thermal ionisation mass spectrometry (CA‐ID‐TIMS) is 48.106 ± 0.023 Ma (2s analytical including tracer uncertainties, MSWD = 1.53) and is our recommended date for GHR1 zircon. Microbeam 206Pb/238U dates from laser ablation‐inductively coupled plasma‐mass spectrometry (LA‐ICP‐MS) and secondary ion mass spectrometry (SIMS) laboratories are reproducible and in agreement with the CA‐ID‐TIMS date to within < 1.5%. Solution multi‐collector ICP‐MS (MC‐ICP‐MS) measurements of Hf isotopes from chemically purified aliquots of GHR1 yield a mean 176Hf/177Hf of 0.283050 ± 17 (2s, n = 10), corresponding to a εHf0 of +9.3. Hafnium isotopic measurements from two LA‐ICP‐MS laboratories are in agreement with the solution MC‐ICP‐MS value. The reproducibility of 206Pb/238U and 176Hf/177Hf ratios from GHR1 zircon across a variety of measurement techniques demonstrates their homogeneity in most grains. Additionally, the effectively limitless reserves of GHR1 material from an accessible exposure suggest that GHR1 can provide a useful reference material for U‐Pb geochronology of Cenozoic zircon and Hf isotopic measurements of zircon with radiogenic 176Hf/177Hf.

A Simplified Method Using a Single N,N,N',N'-Tetraoctyl Diglycolamide Resin Column for the Purification of Sr, Nd and Hf in Geological Materials and the Determination of Their Isotopic Ratios by Multi-collector Inductively Coupled Plasma-Mass Spectrometry.

A simplified method using a single column of N,N,N',N'-tetraoctyl diglycolamide (TODGA) resin is developed for the separation of Sr, Nd and Hf with matrix and interference elements from geological samples, and for subsequent determination of their isotopic ratios by multi-collector inductively coupled plasma-mass spectrometry (MC-ICP-MS). The analytes of Sr, Nd and Hf are absorbed by the TODGA resin and eluted with 6 mol/L HNO3, 1.2 mol/L HCl and 1 mol/L HNO3-1.6 mol/L HF, respectively. The separation procedure is validated by the certified reference materials (CRMs) of BHVO-2, BCR-2 and AGV-2 with analyte recovery greater than 97%. The ratios are measured for 87Sr/86Sr, 143Nd/144Nd and 176Hf/177Hf and the mean values (2σ) are 0.703455 (16), 0.512977 (12) and 0.283108 (8) for BHVO-2, 0.705008 (18), 0.512633 (10) and 0.282878 (4) for BCR-2, and 0.703989 (20), 0.512791 (8) and 0.282982 (8) for AGV-2, which are consistent with the certified values.

The application of abundance sensitivity filters to the precise and accurate measurement of uranium series nuclides by plasma mass spectrometry

Application of retardation filters has revolutionized the use of multi-collector inductively coupled plasma mass spectrometry (MC-ICPMS) for the measurement of U-series disequilibria. Here, we present an evaluation of the application of retardation energy filters coupled with ion counting detectors for the measurement of U-series disequilibria by MC-ICPMS. We show that: 1) The RPQ minimizes backgrounds caused by ions experiencing irregular flight paths at high masses of uranium series nuclides. This reduced background is important for low count rate measurements and has enabled us to develop an improved method for the determination of 226Ra/228Ra ratios using a dual SEM/RPQ collector block. 2) Systematic biases exist for isotope ratios of 234U/238U and 230Th/232Th without the use of RPQs; thus, the RPQ is important for measurement of both of these isotope ratios. 3) That the RPQ makes possible 210Pb measurements in geologic samples using MC-ICPMS, but that this application is limited to samples that have low common Pb, such as carbonates and silica sinter. Additionally, we present mass spectrometric and gamma counting data for U-Th-Ra disequilibria in rock standard reference materials including AGV-2, AThO, BCR-1, BCR-2, BHVO-2, BIR-1a, DTS-1, PCC-1, RGM-2, TML, and W-2a. Comparing this new data with values from published literature enables us to provide consensus or recommended values for U, Th, and 226Ra concentrations and 230Th/232Th ratios for each of these standards. We note that this is the first compilation of recommended radium concentrations for rock standard reference materials.

Vanadium isotope composition of seawater

The speciation, burial, and isotopic composition of vanadium (V) in seawater is predicted to be closely coupled to the redox state of the oceans. While the speciation and burial terms are reasonably constrained, the V isotopic composition of seawater has remained elusive owing to significant analytical challenges. To this end, for the first time we have developed and validated a new method to purify V from large volume (≥500 mL) seawater samples that we used to determine the V isotopic composition of seawater. Our method comprises four discrete V-purification steps that exploit ion-exchange chromatography including Nobias chelate and anion exchange resin(s) and measurement by multi-collector inductively-coupled plasma mass spectrometry. Results from several samples with addition of standard V solution with known isotope composition show no isotopic deviation in the chemical and/or analytical procedures and our reproducibility is within typical analytical error for vanadium isotopes measurements. Though V yields were non-quantitative (averaging ≈ 70%) for natural seawater samples, our approach was nonetheless validated with additional experiments. Therein, synthetic seawater solutions of known V isotopic composition with concentration similar to natural seawater were used to confirm that there is limited isotope fractionation during analytical procedures with similar yields. We further tested seawater samples using UV radiation, HNO3/HCl oxidation, and High-Pressure Asher treatments to ensure there was limited effects from potential non-dissolved phases or variable V speciation such as organic ligand binding of V. All tests except the High-Pressure Asher samples had similar recoveries (i.e. >70%) and all recorded similar isotopic values within error which suggest our method is robust and reliable for V isotopic measurement of seawater. Using our most optimal method, we report V isotope data for several seawater samples from surface and subsurface Atlantic Ocean and deep Pacific Ocean for the first time. Inter-laboratory sample comparison shows that the data was within analysis error (∼0.15‰, 2SD). Initial results imply that the deep ocean is isotopically homogeneous with respect to V, and the uptake of V in surface waters appear to cause very limited, if any, isotope fractionation as it is within analytical uncertainties. Thus, our results suggest a reference seawater V isotope composition of +0.20 ± 0.15‰ relative to V isotope standard AA solution. This work analyzes the first V isotope value of seawater which provides a key foundation for future work to constrain the modern marine V isotope cycle and budget and application for paleoceanographic research.

Strontium isotope ratios (87 Sr/86 Sr) of human fingernail clippings reveal multiple location signals.

Strontium isotope ratios (87 Sr/86 Sr) in human fingernail keratin tissues have been underexplored for region of origin and travel history reconstruction studies. Here we investigated 87 Sr/86 Sr ratios in fingernail keratin to establish baseline measurements in a resident group and to examine how 87 Sr/86 Sr ratios changed with relocation. Fingernail clippings were collected from resident (n = 10) and non-resident/traveler groups (n = 4 and n = 4) that were part of a larger study in Salt Lake City (UT, USA) from 2015 to 2016. Strontium abundance and 87 Sr/86 Sr ratios were determined via multicollector inductively coupled plasma mass spectrometry (MC-ICP-MS). 87 Sr/86 Sr and oxygen (δ18 O) isotope ratios from the traveler participants were compared to examine temporal patterns. Strontium abundance and 87 Sr/86 Sr ratios in fingernails from the resident group established a baseline against which we could evaluate potential differences in non-resident/traveler groups. Resident 87 Sr/86 Sr ratios remained constant over the study period and were consistent with previously measured tap waters for the area. 87 Sr/86 Sr ratio changes in non-resident/traveler groups were rapid and reflected the current location of the individual within 4-5 weeks of arrival. Lastly, δ18 O and 87 Sr/86 Sr ratios of the same fingernail clippings did not exhibit similar temporal patterns, since fingernail δ18 O ratios required more time to attain values characteristic of the new environment. Our findings suggest that strontium is incorporated into fingernail tissues differently from hair and this could be advantageous to forensic investigations. We found that 87 Sr/86 Sr and δ18 O ratios of the same fingernail clippings revealed two different time points reflecting an individual's residence over short- (4-5 weeks, 87 Sr/86 Sr ratios) and long-term (3-5 months, δ18 O values) time scales. It is likely that the 87 Sr/86 Sr ratios of fingernail clippings reflect exogenous signals that are incorporated through bathing waters and that these signals change rapidly with movement to a new location. Our results may aid future forensic studies in the determination of region of origin in unidentified remains.

Mineralogical thallium geochemistry and isotope variations from igneous, metamorphic, and metasomatic systems

This study presents new thallium (Tl) concentration and isotopic composition data for potassium feldspar (K-feldspar), micas, sulfides, and other minerals using solution multi-collector inductively-coupled plasma mass spectrometry (MC-ICP-MS). The samples studied represent a diverse set of igneous, metamorphic, and metasomatic rock types. Purified separates of minerals anticipated to be Tl-bearing were analyzed; in many cases coexisting minerals were measured to examine the distribution of Tl and its isotopes between coexisting phases. This study is the first of its kind to document mineralogical controls on Tl chemical and isotopic fractionation.Thallium contents in rock-forming minerals and common sulfides vary from below detection limit (here, approximately 0.2 ppm Tl in the mineral utilizing an IsoProbe MC-ICP-MS) to 3200 ppm. In this present study, mica and feldspar samples can reach Tl concentrations well over 20 ppm, compared to only 0.7 ppm in average crust. In contrast, only 14 of 38 common sulfide samples contain Tl at levels above the detection limit. Measured Tl isotope ratios, reported as ε205Tl relative to the NIST 997 standard solution, range from −12.1 ± 0.6 to +18.0 ±1.4 (2σ). Most samples analyzed fall within the published range of ε205Tl (−20 to +15) (Nielsen et al., 2017). Although most sulfides show limited Tl enrichment, they display the highest ε205Tl values among coexisting minerals, with Fe-rich micas having the lowest ε205Tl values.The patterns in enrichment are best interpreted to reflect crystal chemical differences and the incompatible, dominantly lithophile nature of Tl. In turn, isotopic fractionation also reflects control by the bonding environment as well as redox conditions. The preferential distribution of Tl into micas and K-feldspar found here is consistent with the similarity in charge and ionic radius of Tl+ and K+. The higher ε205Tl values in sulfides agree with previous observations and theoretical studies showing the tendency of covalent bonds, high bond strengths, and high oxidation states to favor heavy isotopes. This work highlights important areas for future research regarding the natural weathering of Tl-bearing substrates, understanding regional cycling of Tl, and potential bioremediation of Tl contamination.