High-precision Isotope Measurements Research Articles

A single-column separation procedure for Sr, Nd, and Sm in small-size samples and high-precision isotope measurements using a TIMS with 1013 and 1012 Ω amplifiers

A single-column separation procedure for Sr, Nd, and Sm in small-size samples and high-precision isotope measurements using a TIMS with 1013 and 1012 Ω amplifiers.

Origin of carbonatites and associated silicate rocks revealed by Mg triple-isotope approach

Carbonatites are rare carbonate-rich igneous rocks derived from carbon and carbonate-rich regions of Earth's mantle. Although a number of igneous processes are recognized to have controlled their compositions, the origin of the carbonate-rich nature of these magmas remains debated and has been linked to various mantle-related processes, including subduction and plume–lithosphere interaction. High-precision isotope measurements can provide insights into carbonatite petrogenesis, including the identification of subducted crustal material in their source region. In particular, combining mass-dependent and kinetically corrected Mg isotope data, also known as the triple-isotope approach, provides insights into mass fractionation processes driving mass dependent fractionation, which in turn allows to distinguish between equilibrium and kinetic processes. In this work, we report high-precision Mg stable isotope data for 59 carbonatites and associated silicate rocks from different localities and ages ranging from 3000 Ma to present-day, as well as C and O isotopic analysis for 38 carbonatites and Sr isotopic analysis for 41 carbonatites and silicate rocks. In addition, we also report Mg isotope data for 17 Phanerozoic carbonate rocks, with the aim of identifying the isotopic signature of carbonate-rich material potentially recycled to the carbonatite mantle source regions. Collectively, the data reveal a range of stable Mg isotope compositions from δ25/24MgDTS-2 = −1.20 ± 0.01‰ to +0.08 ± 0.01‰. We observe positive residual deviations after kinetic mass fractionation correction of the Mg isotope data for our carbonatites; an isotope signal that is also present in Phanerozoic carbonates. This observation establishes that a component of the Mg present in these samples experienced mass-dependent equilibrium isotopic fractionation processes, which are significantly larger at low temperatures. Given that the Mg results do not covary with C and O isotopic signals, the magnitude of the fractionation following the equilibrium law observed in carbonatites provides strong evidence for recycled material from the Earth's surface in the mantle source of Ca- and Mg-rich carbonatites. Furthermore, associated silicate rocks present mantle-like Mg isotopic compositions in contrast with the genetically linked carbonatites - based on the Sr isotopes - for some complexes, which is best explained if the carbonatites and associated silicate rocks represent distinct generation of partial melts of a mantle source containing recycled carbonate.

Sources, seasonal cycling, and fate of plutonium in a seasonally stratified and radiologically contaminated pond

Unlike short-term laboratory experiments, studies at sites historically contaminated with radionuclides can provide insight into contaminant migration behavior at environmentally-relevant decadal timescales. One such site is Pond B, a seasonally stratified reservoir within Savannah River Site (SC, USA) has low levels (μBq L−1) of plutonium in the water column. Here, we evaluate the origin of plutonium using high-precision isotope measurements, investigate the impact of water column geochemistry on plutonium cycling during different stratification periods, and re-evaluate long-term mass balance of plutonium in the pond. New isotopic data confirm that reactor-derived plutonium overwhelms input from Northern Hemisphere fallout at this site. Two suggested mechanisms for observed plutonium cycling in the water column include: (1) reductive dissolution of sediment-derived Fe(III)-(oxyhydr)oxides during seasonal stratification and (2) plutonium stabilization complexed strongly to Fe(III)-particulate organic matter (POM) complexes. While plutonium may be mobilized to a limited extent by stratification and reductive dissolution, peak plutonium concentrations are in shallow waters and associated with Fe(III)-POM at the inception of stratification. This suggests that plutonium release from sediments during stratification is not the dominant mechanism driving plutonium cycling in the pond. Importantly, our analysis suggests that the majority is retained in shallow sediments and may become increasingly recalcitrant.

Multi-collector Inductively Coupled Plasma Mass Spectrometry: New Developments and Basic Concepts for High-precision Measurements of Mass-dependent Isotope Signatures

Due to the development of multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) around 25 years ago, the isotopes of a large range of elements (masses from Li to U) are now analyzed with high enough precision and accuracy to resolve subtle natural variations. These so-called 'non-traditional stable isotope systems' opened many new research avenues and are applied at an increasing rate in research and industry projects and in a broad range of different disciplines, including archeology, biology, physics, cosmochemistry and geology. Here, we briefly summarize the most basic concepts of MC-ICP-MS, introduce new technical developments and address important points on how to acquire accurate high-precision isotope measurements of non-traditional stable isotopes.

High-precision determination of stable potassium and magnesium isotopes utilizing single column separation and multicollector inductively coupled plasma mass spectrometry

With advances in analytical precision by multicollector inductively coupled plasma mass spectrometry, K and Mg isotopes are increasingly used as a combined tool in tracing sources and processes in geoscientific research. However, reported methods in the literature require at least two column separation procedures during sample purification, which is time-consuming (at least two days). Therefore, a single column procedure could improve efficiencies, and these efforts are necessary to extend the combined application of K and Mg isotopes as geological tracers. In this study, a simple and time-efficient chromatographic procedure was reported, utilizing a single column for quantitative separation of both K and Mg from sample matrices for high-precision isotopic measurement of K and Mg. Using this novel method, the results for international geological standards agreed with published values, verifying the robustness of the procedure. The popularization of this optimized procedure would potentially extend the combined application of K and Mg isotopes in geological studies.

The iron did it

Atmospheric Oxygen What factors controlled the accumulation of atmospheric oxygen gas (O2) early in the history of Earth? Heard et al. used high-precision iron isotopic measurements of Archean-Paleoproterozoic sediments, with ages between 3.8 billion and 2.3 billion years ago, and laboratory data about synthetic pyrites to show that pyrite, or iron sulfide, burial could have resulted in net O2 export. These reactions therefore may have contributed to early episodes of transient oxygenation before the Great Oxidation Event that began about 2.4 billion years ago. Science , this issue p. [446][1] [1]: /lookup/doi/10.1126/science.aaz8821

Further Evaluation for High-precision Isotopic Measurement of 205Pb-spiked Pb by Dynamic Multiple Ion Counting

Further Evaluation for High-precision Isotopic Measurement of 205Pb-spiked Pb by Dynamic Multiple Ion Counting

Chemical procedure for Zn purification and double spike method for high precision measurement of Zn isotopes by MC-ICPMS

We have developed a new technique for Zn separation and high precision isotope measurement of geological and cosmochemical samples. The protocol includes sample digestion, chemical separation and purification with ion-exchange chromatography and a double spike isotopic measurement using a MC-ICPMS. An analytical precision of 0.02‰ (2SD) for 66Zn/64Zn was obtained by multiple measurements of a secondary standard (JMC-Lyon). In order to test the accuracy of our method, we analyzed the Zn isotopic composition of the geological reference materials BHVO-2, AGV-2, BIR-1, BCR-2 and JB-2, which are consistent with previous measurements from the literature. The measurements of geological reference standards show an external reproducibility ranging between 0.02 and 0.05‰ (2SD). This study provides a high precision and accuracy Zn isotope double spike technique for geological and cosmochemical rock samples, while requiring only 28 ng Zn per analysis, and is therefore suitable for the study of high temperature igneous or cosmochemical processes.

Precise determination of Ar, Kr and Xe isotopic fractionation due to diffusion and dissolution in fresh water

Dissolved noble gases are ideal conservative tracers of physical processes in the Earth system due to their chemical and biological inertness. Although bulk concentrations of dissolved Ar, Kr, and Xe are commonly measured to constrain physical models of atmosphere, ocean, and terrestrial hydrosphere processes, stable isotope ratios of these gases (e.g. 136Xe/129Xe) are seldom used because of low signal-to-noise ratios. Here we present the first results from a new method of dissolved gas sampling, extraction and analysis that permits measurement of stable Ar, Kr, and Xe isotope ratios at or below ∼5 per meg amu−1 precision (1σ), two orders-of-magnitude below conventional Kr and Xe isotopic measurements. This gain in precision was achieved by quantitative extraction and subsequent purification of dissolved noble gases from 2-L water samples via helium sparging and viscous dual-inlet isotope ratio mass spectrometry. We have determined the solubility fractionation factors (αsol) for stable Ar, Kr, and Xe isotope ratios between ∼2 and 20°C via laboratory equilibration experiments. We have also conducted temperature-controlled air-water gas exchange experiments to estimate the kinetic fractionation factors (αkin) of these isotope ratios. We find that both αsol and αkin, normalized by isotopic mass difference (Δm), decrease in magnitude with atomic number but are proportional to Δm for isotope ratios of the same element. With the new ability for high precision isotopic measurements, we suggest that dissolved Kr and Xe isotope ratios in groundwater represent a promising, novel geochemical tool with important applications for groundwater modeling, water resource management, and paleoclimate.

Extraction of Pb and Zn from crude oil for high-precision isotopic analysis by MC-ICP-MS

Radiogenic and stable isotopic tracing of crude oils has not so far been undertaken, largely because of the difficulties of dealing with the low trace element contents of oil samples for high-precision isotopic measurements. Here, we present a novel analytical protocol that allows for precise and accurate determination of radiogenic Pb and stable Zn isotopic compositions on as little as 5 ml of crude oil from a variety of geographically, geologically, and environmentally diverse settings. The 41 Pb and Zn samples measured to validate the new protocol were separated from their respective crude oils by liquid-liquid extraction into an aqueous phase readily handled in a clean laboratory for subsequent purification of Pb and Zn by standard anion-exchange column chromatography. Lead and Zn isotopic compositions on the same 5 ml sample of crude oil were obtained by MC-ICP-MS on 95% of the total extracted Pb and Zn, while elemental concentrations were measured by Q-ICP-MS on 5% aliquots. To the best of our knowledge, the present technique is the first efficient procedure for Pb and Zn isotopic analysis of crude oil, which, owing to the elimination of the organic fraction at the liquid-liquid extraction stage, does not require any specialized equipment, neither for the wet chemistry nor for the mass spectrometry. The high extraction yields of the method and the low detection limits and high sensitivity of, respectively, Q-ICP-MS and MC-ICP-MS permit analysis of very small sample quantities (down to 2 ng and 100 ng, respectively, of Pb and Zn for isotopic analysis, and a few hundred pg for abundance measurements). Reproducibility is on a par with routine state-of-the-art Pb and Zn isotopic measurements of other types of geological materials, while total procedural blanks for both elements are negligible relative to the amounts of Pb and Zn typically separated from crude oil.

A novel sample cell for reducing the “Position Effect” in laser ablation MC-ICP-MS isotopic measurements

A novel laser ablation cell geometry significantly reduces the so-called position effect on high precision and accuracy isotopic measurements by Laser Ablation-Multiple Collector-Inductively Coupled Plasma-Mass Spectrometry (LA-MC-ICP-MS).

An improved extraction chromatographic purification of tungsten from a silicate matrix for high precision isotopic measurements using MC-ICPMS

An improved chemical method is developed to accurately measure the W isotopic compositions of silicate samples with a precision of better than ±0.05ε on ε182W.

Double-spike inversion for three-isotope systems

Double spiking is conventionally used to make accurate determinations of natural mass-dependent isotopic fractionations for elements with four or more stable isotopes. Here we document a methodology which extends the effective application of double spiking to three isotope systems. This approach requires making a mixture with isotope ratios that lie on a ‘critical curve’ where the sample – double-spike mixing line and the tangent to the instrumental mass-bias curve are coincident. Inversion of the mixing equations for such a mixture leads to a solution for the sample fractionation which is independent (to first order) of the uncertainty in the instrumental mass-bias and, hence, independent of any mass-dependent artefacts in the measurement such as those produced by residual matrix not completely removed by prior chemical purification. In practice, mixtures can be made which yield an accuracy conservatively estimated to be ∼ 0.005‰/amu. The precision of the method is explored as a function of double-spike composition for Mg, Si and K isotope systems. We show that for Mg and Si measurement precision is not compromised by the compositions of viable critical mixtures nor by uncertainty magnification during inversion of the equations. Thus, double spiking provides a valuable means to obtain robust, high precision isotopic measurements of Mg and Si. For K, however, the low abundance of 40K in the optimal critical mixture places a significant practical limitation on the application of double spiking to analyses of this element.

Evaluation of carrier gases for high-precision water isotopic measurements by cavity ring-down laser spectroscopy

ABSTRACTThe carrier gas is important for obtaining stable, precise hydrogen and oxygen isotopic ratios in water samples using cavity ring-down laser spectroscopy. The δ2H and δ18O variations were investigated using four carrier gases under two microcombustion conditions. Although most deviations of δ2H and δ18O values were within the standard deviation of the instrument, statistical analysis indicated that carrier gas provided by a drying tube with higher water background was not suitable for cavity ring-down laser spectroscopy. In addition, the microcombustion on condition did not significantly improve the precision and accuracy of δ2H and δ18O measurements. Therefore, the best method for achieving highly precise results involved the use of low water containing compressed air as the carrier gas with the microcombustion warm condition.

Cryogenic distillation facility for isotopic purification of protium and deuterium.

Isotopic purification of the protium and deuterium is an important requirement of many physics experiments. A cryogenic facility for high-efficiency separation of hydrogen isotopes with a cryogenic distillation column as the main element is described. The instrument is portable, so that it can be used at the experimental site. It was designed and built at the Petersburg Nuclear Physics Institute, Gatchina, Russia. Fundamental operating parameters have been measured including a liquid holdup in the column packing, the pressure drops across the column and the purity of the product at different operating modes. A mathematical model describes expected profiles of hydrogen isotope concentration along the distillation column. An analysis of ortho-parahydrogen isomeric composition by gas chromatography was used for evaluation of the column performance during the tuning operations. The protium content during deuterium purification (≤100 ppb) was measured using gas chromatography with accumulation of the protium in the distillation column. A high precision isotopic measurement at the Institute of Particle Physics, ETH-Zurich, Switzerland, provided an upper bound of the deuterium content in protium (≤6 ppb), which exceeds all commercially available products.

The earliest Lunar Magma Ocean differentiation recorded in Fe isotopes

Recent high-precision isotopic measurements show that the isotopic similarity of Earth and Moon is unique among all known planetary bodies in our Solar System. These observations provide fundamental constraints on the origin of Earth–Moon system, likely a catastrophic Giant Impact event. However, in contrast to the isotopic composition of many elements (e.g., O, Mg, Si, K, Ti, Cr, and W), the Fe isotopic compositions of all lunar samples are significantly different from those of the bulk silicate Earth. Such a global Fe isotopic difference between the Moon and Earth provides an important constraint on the lunar formation – such as the amount of Fe evaporation as a result of a Giant Impact origin of the Moon. Here, we show through high-precision Fe isotopic measurements of one of the oldest lunar rocks (4.51±0.10 Gyr dunite 72 415), compared with Fe isotope results of other lunar samples from the Apollo program, and lunar meteorites, that the lunar dunite is enriched in light Fe isotopes, complementing the heavy Fe isotope enrichment in other lunar samples. Thus, the earliest olivine accumulation in the Lunar Magma Ocean may have been enriched in light Fe isotopes. This new observation allows the Fe isotopic composition of the bulk silicate Moon to be identical to that of the bulk silicate Earth, by balancing light Fe in the deep Moon with heavy Fe in the shallow Moon rather than the Moon having a heavier Fe isotope composition than Earth as a result of Giant Impact vaporization.

Tungsten isotopes in bulk meteorites and their inclusions-Implications for processing of presolar components in the solar protoplanetary disk.

We present high precision, low- and high-resolution tungsten isotope measurements of iron meteorites Cape York (IIIAB), Rhine Villa (IIIE), Bendego (IC), and the IVB iron meteorites Tlacotepec, Skookum, and Weaver Mountains, as well as CI chondrite Ivuna, a CV3 chondrite refractory inclusion (CAI BE), and terrestrial standards. Our high precision tungsten isotope data show that the distribution of the rare p-process nuclide 180W is homogeneous among chondrites, iron meteorites, and the refractory inclusion. One exception to this pattern is the IVB iron meteorite group, which displays variable excesses relative to the terrestrial standard, possibly related to decay of rare 184Os. Such anomalies are not the result of analytical artifacts and cannot be caused by sampling of a protoplanetary disk characterized by p-process isotope heterogeneity. In contrast, we find that 183W is variable due to a nucleosynthetic s-process deficit/r-process excess among chondrites and iron meteorites. This variability supports the widespread nucleosynthetic s/r-process heterogeneity in the protoplanetary disk inferred from other isotope systems and we show that W and Ni isotope variability is correlated. Correlated isotope heterogeneity for elements of distinct nucleosynthetic origin (183W and 58Ni) is best explained by thermal processing in the protoplanetary disk during which thermally labile carrier phases are unmixed by vaporization thereby imparting isotope anomalies on the residual processed reservoir.

The chronology of planetary embryos

Planetary Formation Protoplanets, or early planetary embryos such as iron meteorite parent bodies, formed in the early protoplanetary disk from dust, debris, and planetesimals. Defining the precise chronology of accretion and differentiation—including core formation—of these planetary embryos will aid in a richer understanding of the chemical evolution of the solar system. Through high-precision tungsten isotope measurements, Kruijer et al. show that the timing of accretion and core formation for iron meteorite groups falls within 0.6 to 2 million years of the age of the solar system (see the Perspective by Elliott). Differences of timing within this group are probably a function of volatile contents of the parent bodies or spatial and chemical heterogeneity within the protoplanetary disk. Science , this issue p. [1150][1]; see also p. [1086][2] [1]: /lookup/volpage/344/1150?iss=6188 [2]: /lookup/volpage/344/1086?iss=6188

High precision osmium elemental and isotope measurements of North Atlantic seawater

This study presents new Os isotope and elemental data of seawater from the North Atlantic Ocean.

Maintaining consistent traceability in high-precision isotope measurements of CO<sub>2</sub>: a way to verify atmospheric trends of δ<sup>13</sup>C and δ<sup>18</sup>O

Abstract. Maintaining consistent traceability of high-precision measurements of CO2 isotopes is critical in order to obtain accurate atmospheric trends of δ13C and δ18O (in CO2). Although a number of laboratories/organizations around the world have been conducting baseline measurements of atmospheric CO2 isotopes for several decades, reports on the traceability and maintenance are rare. In this paper, a principle and an approach for maintaining consistent traceability in high-precision isotope measurements (δ13C and δ18O) of atmospheric CO2 are described. The concept of Big Delta is introduced and its role in maintaining traceability of the isotope measurements is described and discussed extensively. The uncertainties of the traceability have been estimated based on annual calibration records over the last 10 yr. The overall uncertainties of CO2 isotope measurements for individual ambient samples analyzed by the program at Environment Canada have been estimated (excluding these associated with the sampling). The values are 0.02 and 0.05‰ in δ13C and δ18O, respectively, which are close to the World Meteorological Organization (WMO) targets for data compatibility. The annual rates of change in δ13C and δ18O of the primary anchor (which links the flask measurements back to the VPDB-CO2 scale) are close to zero (−0.0016 ± 0.0012‰, and −0.006 ± 0.003‰ per year, respectively) over a period of 10 yr (2001–2011). The average annual changes of δ13C and δ18O in air CO2 at Alert GAW station over the period from 1999 to 2010 have been evaluated and confirmed; they are −0.025 ± 0.003‰ and 0.000 ± 0.010‰, respectively. The results are consistent with a continuous contribution of fossil fuel CO2 to the atmosphere, having a trend toward more negative in δ13C, whereas the lack of change in δ18O likely reflects the influence from the global hydrologic cycle. The total change of δ13C and δ18O during this period is ~0.27‰ and ~0.00‰, respectively. Finally, the challenges and recommendations as strategies to maintain a consistent traceability are described.