High-precision Isotope Ratio Measurements Research Articles

Optically Switched Dual-Wavelength Cavity Ring-Down Spectrometer for High-Precision Isotope Ratio Measurements of Methane δD in the Near Infrared.

We report a spectrometer employing optically switched dual-wavelength cavity ring-down spectroscopy (OSDW-CRDS) for high-precision measurements of methane isotope ratios. A waveguide optical switch rapidly alternated between two wavelengths to detect absorption by two isotopologues using near-infrared CRDS. This approach alleviated common-mode noise that originated primarily from temperature and frequency fluctuations. We demonstrated the measurement of δD in natural abundance methane to a precision of 2.3 ‰, despite the lack of active temperature or frequency stabilization of the cavity. The ability of alternating OSDW-CRDS to improve the isotope precision in the absence of cavity stabilization were measured by comparing the Allan deviation with that obtained when frequency-stabilizing the cavity length. The system can be extended to a wide variety of applications such as isotope analysis of other species, kinetic isotope effects, ortho-para ratio measurements, and isomer abundance measurements. Furthermore, our technique can be extended to multiple isotope analysis or two species involved in kinetics studies through the use of multiport or high-speed optical switches, respectively.

High-precision isotopic analysis of serum and whole blood Cu, Fe and Zn to assess possible homeostasis alterations due to bariatric surgery.

Bariatric surgery is an effective procedure to achieve weight loss in obese patients. However, homeostasis of essential metals may be disrupted as the main absorption site is bypassed. In this study, we determined Cu, Fe and Zn isotopic compositions in paired serum and whole blood samples of patients who underwent Roux-en-Y gastric bypass (RYGB) surgery for evaluation of longitudinal changes and their potential relation to mineral element concentrations and relevant clinical parameters used for monitoring the patient's condition. Samples from eight patients were collected pre-surgery and at 3, 6 and 12 months post-surgery. Multi-collector inductively coupled plasma-mass spectrometry (MC-ICP-MS) was used for high-precision isotope ratio measurements. Alterations in metal homeostasis related to bariatric surgery were reflected in the serum and whole blood Cu, Fe and Zn isotopic compositions. The serum and whole blood Cu became isotopically lighter (lower δ65Cu values) after bariatric surgery, reaching statistical significance at 6 months post-surgery (p < 0.05). The difference between the serum and the whole blood Zn isotopic composition increased after surgery, reaching significance from 6 months post-surgery onwards (p < 0.05). Those changes in Cu, Fe and Zn isotopic compositions were not accompanied by similar changes in their respective concentrations, making isotopic analysis more sensitive to physiological changes than elemental content. Furthermore, the Zn isotopic composition correlates with blood glycaemic and lipid parameters, while the Fe isotopic composition correlates with glycaemic parameters. Graphical Abstract.

Rubidium isotopic composition of the Earth, meteorites, and the Moon: Evidence for the origin of volatile loss during planetary accretion

Understanding the origin of volatile element variations in the inner Solar System has long been a goal of cosmochemistry, but many early studies searching for the fingerprint of volatile loss using stable isotope systems failed to find any resolvable variations.An improved method for the chemical purification of Rb for high-precision isotope ratio measurements by multi-collector inductively-coupled-plasma mass-spectrometry. This method has been used to measure the Rb isotopic composition for a suite of planetary materials, including carbonaceous, ordinary, and enstatite chondrites, as well as achondrites (eucrite, angrite), terrestrial igneous rocks (basalt, andesite, granite), and Apollo lunar samples (mare basalts, alkali suite). Volatile depleted bodies (e.g. HED parent body, thermally metamorphosed meteorites) are enriched in the heavy isotope of Rb by up to several per mil compared to chondrites, suggesting volatile loss by evaporation at the surface of planetesimals. In addition, the Moon is isotopically distinct from the Moon in Rb. The variations in Rb isotope compositions in the volatile-poor samples are attributed to volatile loss from planetesimals during accretion. This suggests that either the Rb (and other volatile elements) were lost during or following the giant impact or by evaporation earlier during the accretion history of Theia.

Integrated Extraction Chromatographic Separation of the Lithophile Elements Involved in Long-Lived Radiogenic Isotope Systems (Rb-Sr, U-Th-Pb, Sm-Nd, La-Ce, and Lu-Hf) Useful in Geochemical and Environmental Sciences.

A fast and efficient sample preparation method in view of isotope ratio measurements is described, allowing the separation of 11 elements involved, either as "parent" or as "daughter" isotopes, in six radiogenic isotope systems used as chronometers and tracers in earth, planetary, and environmental sciences. The protocol is based on small extraction chromatographic columns, used either alone or in tandem, through which a single nitric acid solution is passed, without any intervening evaporation step. The columns use commercially available extraction resins (Sr resin, TRU resin, Ln resin, RE resin, and again Ln resin for isolating Sr and Pb, LREE then La-Ce-Nd-Sm, Lu(Yb), and Hf, Th, and U, respectively) along with an additional, in-house prepared resin for separating Rb. A simplified scheme is proposed for samples requiring the separation of Sr, Pb, Nd, and Hf only. Adverse effects of troublesome major elements (Fe3+, Ti) are circumvented by masking with ascorbic acid and hydrofluoric acid, respectively. Typical recoveries in the 85-95% range are achieved, with procedural blanks of 10-100 pg, negligible with regard to the amounts of analytes processed. The fractions separated are suitable for high precision isotope ratio measurements by TIMS or MC-ICP-MS, as demonstrated by the repeat analyses of several international reference materials of basaltic composition for 87Sr/86Sr, 208,207,206Pb/204Pb, 143Nd/144Nd, 176Hf/177Hf, and 230Th/232Th. Concentration data could be obtained by spiking and equilibrating the sample with appropriate isotopic tracers before the onset of the separation process and, finally, measuring the isotope ratios modified by the isotope dilution process.

An inter-laboratory comparison of high precision stable isotope ratio measurements for nanoparticle tracing in biological samples

Stable isotope labeling coupled with high precision isotope ratio measurements by multiple collector-ICP-MS is effective for tracing zinc from zinc oxide nanoparticles (ZnO NPs) in complex media and against a high zinc background. Using this technique, a previous study detected a slightly enhanced uptake of Zn in the blood of human females following dermal exposure to a sunscreen containing ZnO NPs, relative to a sunscreen of the same formulation but with larger ZnO particles (‘bulk’ material). Until now, the results of these exposures and the accuracy of the analyses, which require the resolution of subtle differences in Zn isotope ratios, have not been independently confirmed. Here we compare data from the previous study with results obtained in new, independent analyses of the same and additional samples, that were performed using similar techniques and instrumentation but in a different laboratory. The data sets are in good agreement, with a Pearson correlation coefficient of r ≈ 0.98, thus establishing the usefulness of the methods for tracing engineered ZnO NPs (and other anthropogenic sources of Zn) in Zn-rich biological materials. Previously unanalyzed blood samples from the earlier study provide further evidence for the increased uptake of Zn from ZnO NPs relative to bulk ZnO and they confirm that uptake rates decrease once sunscreen application has ceased.

Compact multipass optical cell for laser spectroscopy

A multipass cell (MPC) design for laser absorption spectroscopy is presented. The development of this new type of optical cell was driven by stringent criteria for compactness, robustness, low volume, and ease of use in optical systems. A single piece of reflective toroidal surface forms a near-concentric cavity with a volume of merely 40 cm(3). Contrary to traditional MPCs, this design allows for flexible path-length adjustments by simply changing the aiming angle of the laser beam at the entrance window. Two effective optical path lengths of 2.2 and 4.1 m were chosen to demonstrate the cell's suitability for high-precision isotope ratio measurements of CO(2) at 1% and ambient mixing ratio levels.

Rubidium isotopes in primitive chondrites: Constraints on Earth's volatile element depletion and lead isotope evolution

The bulk silicate Earth (BSE) shows substantial deficits in volatile elements compared to CI-chondrites and solar abundances. These deficits could be caused by pre-accretionary depletion in the solar nebula during condensation of solids, or by later heat-driven evaporation during collision of small bodies that later accreted to form the Earth. The latter is considered to result in isotope fractionation for elements with low condensation temperatures that correlates with the degree of depletion. Here, we report first high-precision isotope ratio measurements of the moderately volatile and lithophile trace element Rb. Data from seventeen chondrite meteorites show that their Rb isotope abundances are nearly indistinguishable from Earth, not deviating more than 1 per mil in their 87Rb/85Rb. The almost uniform solar system Rb isotope pool suggests incomplete condensation or evaporation in a single stage is unlikely to be the cause of the volatile element deficit of the Earth. As Rb and Pb have similar condensation temperatures, we use their different degrees of depletion in the BSE to address the mechanisms and timing of terrestrial volatile depletion. The Rb isotope data are consistent with a scenario in which the volatile budget of the Earth was generated by a mixture of a highly volatile-element depleted early Proto-Earth with undepleted material in the course of terrestrial accretion. Observed Pb and Rb abundances and U–Pb and Rb–Sr isotope systematics suggest that volatile addition occurred at approximately the same time at which last core–mantle equilibration was achieved. In line with previous suggestions, this last equilibration involved a second stage of Pb (but not Rb) depletion from the BSE. The timing of this second Pb loss event can be constrained to ~110Ma after the start of the solar system. This model supports a scenario with core storage of Pb in the aftermath of a putative Moon forming giant impact that also delivered the bulk of the volatile elements to the Earth.

Continuous isotopic composition measurements of tropospheric CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; at Jungfraujoch (3580 m a.s.l.), Switzerland: real-time observation of regional pollution events

Abstract. A quantum cascade laser based absorption spectrometer (QCLAS) is applied for the first time to perform in situ, continuous and high precision isotope ratio measurements of CO2 in the free troposphere. Time series of the three main CO2 isotopologue mixing ratios (12C16CO2, 13C16CO2 and 12C18O16O) have simultaneously been measured at one second time resolution over two years (from August 2008 to present) at the High Altitude Research Station Jungfraujoch (3580 m a.s.l., Switzerland). This work focuses on periods in February 2009 only, when sudden and pronounced enhancements in the tropospheric CO2 were observed. These short-term changes were closely correlated with variations in CO mixing ratios measured at the same site, indicating combustion related emissions as potential source. The analytical precision of 0.046‰ (at 50 s integration time) for both δ13C and δ18O and the high temporal resolution allowed the application of the Keeling plot method for source signature identification. The spatial origin of these CO2 emission sources was then determined by backward Lagrangian particle dispersion simulations.

Precise isotope ratio measurements by MC-ICP-MS and application of the isotope dilution technique for the determination of germanium in the Gallium Neutrino Observatory

Summary In the Gallium Neutrino Observatory (GNO) experiment solar neutrinos are studied. Low energy neutrinos interact with 71Ga producing radioactive 71Ge, which decays with a half-life of 11.43 days back to 71Ga. This β+-decay is used for quantifying the number of solar neutrinos observed. Stable Ge isotopes are used as carriers when 71Ge atoms are extracted from the GaCl3 target for measuring their decay. The carrier serves at the same time for quantification of the chemical yield of the extraction process. Ge-removal from the GaCl3 detector solution proceeds exponentially and a small amount of Ge carrier remains in the Ga-tank, which is removed only during the following extraction(s). The use of different stable enriched Ge isotopes (70Ge, 72Ge, 74Ge and 76Ge) in alternating sequence allows one to determine the extraction yield of the carrier by high precision isotope ratio measurements. The measurements are carried out using multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS). The exact quantification of any residual Ge carrier from the preceding run is achieved through isotope dilution calculations and isotope mixture calculations. In this paper we describe the evaluation of the results using the two-isotopes and two-components approach, as well as the multi-isotope and three-components approaches. We could demonstrate that the measured isotopic composition of the carrier after extraction can be fully modelled by a mixture of the initially used Ge carrier, of the Ge carrier from the previous run and of a small, but non-negligible contribution of a natural Ge contamination.

High precision and continuous field measurements of δ 13C and δ 18O in carbon dioxide with a cryogen-free QCLAS

The present paper describes a compact and cryogen-free, quantum cascade laser based absorption spectrometer (QCLAS) designed for in situ, continuous and high precision isotope ratio measurements of atmospheric CO2. The mobile instrument incorporates several new features including a novel astigmatic multi-pass cell assembly, a quasi-room temperature quantum cascade laser, thermoelectrically cooled detectors as well as a new retrieval approach. The combination of these features now makes it possible to measure isotope ratios of ambient CO2 with a precision of 0.03 and 0.05‰ for δ13C and δ18O, respectively, using a 100 s integration time. A robust and optimized calibration procedure was developed to bring the retrieved isotope ratios on an absolute scale. This assures an accuracy better than 0.1‰ under laboratory conditions. The instrument performance was also assessed in a field campaign in which the spectrometer operated autonomously and provided mixing ratio values for the main three CO2 isotopologues at one second time resolution. An accuracy of 0.2‰ was routinely obtained for both isotope ratios during the entire period. The results were in excellent agreement with the standard laboratory-based isotope ratio mass spectrometer measurements made on field-collected flask samples. A few illustrative examples are used to depict the potential of this optical method in atmosphere–biosphere research.

Selected isotope ratio measurements of light metallic elements (Li, Mg, Ca, and Cu) by multiple collector ICP-MS.

The unique capabilities of multiple collector inductively coupled mass spectrometry (MC-ICP-MS) for high precision isotope ratio measurements in light elements as Li, Mg, Ca, and Cu are reviewed in this paper. These elements have been intensively studied at the Geological Survey of Israel (GSI) and other laboratories over the past few years, and the methods used to obtain high precision isotope analyses are discussed in detail. The scientific study of isotopic fractionation of these elements is significant for achieving a better understanding of geochemical and biochemical processes in nature and the environment.

Atomic spectrometry update. Environmental analysis

This is the twenty-first annual review published in JAAS of the application of atomic spectrometry to the chemical analysis of environmental samples. In the analysis of air, there is ongoing development of instrumentation for the interrogation of particles at the nanometre scale. It would seem that there is continuing interest in the measurement of trace levels of mercury species in the atmosphere, particularly those emissions from point sources such as coal-fired power stations. In the analysis of water, elemental speciation protocols have again received considerable attention and there is a renewed trend for using methods based on vapour generation for the determination of selected elements. Dominant themes in the analysis of soils include the application of sequential extraction techniques and the continuing development of speciation protocols for elements such as As, Hg and Se. Laser ablation is readily being adopted as a solid sampling tool in many geochemical laboratories. In a similar vein, multi-collector ICP-MS is increasingly being used to perform high precision isotope ratio measurements. Not only is the focus on developing robust measurement procedures for routine use but also on carrying out more fundamental work, designed to increase our understanding of these techniques.

Analytical Methods for Non-Traditional Isotopes

This chapter is devoted to the analytical methods employed for making high precision isotope ratio measurements that preserve naturally occurring mass-dependent isotopic variations. The biggest challenge in making these types of measurements is deconvolving mass-dependent isotopic fractionation produced in the laboratory and mass spectrometer, from naturally occurring mass-dependent isotopic fractionation, because the patterns of isotope variation produced by these processes are identical. Therefore, the main theme of this chapter is the description and mathematical treatment of mass-dependent isotopic variations and the possible pitfalls in deconvolving instrumental mass bias from naturally occurring mass-dependent isotopic variations. This chapter will not attempt to catalog methods for isotopic analysis of different elements. These details are better discussed in later chapters where ‘element specific’ analytical issues are covered. Rather, the effort in the chapter will be to focus on those specific items that make mass analysis of non-traditional isotopes challenging and unique, and the methods that can be employed to make precise and accurate isotope ratios. Isotopic analysis of non-traditional isotopes is made using three main types of mass spectrometers. Elements that can easily be introduced as gases, such as Cl or Br, are typically analyzed using a gas source mass spectrometer. In contrast, metal elements are analyzed using either a thermalionization mass spectrometer (TIMS) or a multi-collector inductively coupled plasma mass spectrometer (MC-ICP-MS). The main difference between these three types of instruments is how the sample is introduced into the instrument, and how the sample is ionized. In contrast, the analyzer part of each instrument is similar. All three types of instruments use a stack of lenses with variable potential to focus the ion beam, a magnet to resolve the ion beam into different masses, and a series of collectors to measure ion currents of different isotopes simultaneously. The core of the mass analyzer …

High-precision Cu and Zn isotope analysis by plasma source mass spectrometry

Spectral interferences originating from instrumental and sample-matrix components continue to present a major analytical challenge to high-precision isotope ratio measurements by multiple-collector inductively coupled plasma mass spectrometry (MC-ICP-MS). This is particularly true when measuring stable isotopic variability of Cu and Zn, where instrumental and sample-matrix related spectral components may obscure the very small isotopic anomalies that typify these metals in terrestrial materials. We present a systematic characterisation and quantification of spectral interferences across the mass range 63Cu to 70Zn using two MC-ICP-MS instruments: a Micromass IsoProbe and a VG Axiom. Significant instrumental Ni backgrounds of up to 40 mV total Ni occur on the IsoProbe, reflecting streaming off the Ni-sampler and/or skimmer cones. This Ni contribution, however, is insufficient to account for the excess peak contribution at 64amu, suggestive of an as yet unidentified interference contribution at this mass. By contrast, Ni backgrounds on the Axiom are roughly one order of magnitude lower, and no comparable interference occurs at 64amu. High-resolution mass scans on the Axiom have identified 40Ar12C16O+ and 40Ar14N14N+ species at 68amu and 40Ar14N16O+ at 70amu. Also, HNO3-related 1H1H14N16O16O16O+ and 1H1H14N16O16O18O+ species at 64amu and 66amu respectively were observed on the Axiom using solution nebulisation. None of these species were observed on the IsoProbe, possibly reflecting the effect of an Ar-bled hexapole collision cell that reduces molecular interferences through ion-molecule reactions. Instrumental backgrounds have been successfully corrected using an on-peak acid blank subtraction procedure. Zinc hydride adducts occur on the Axiom using solution nebulisation. These interferences are eliminated using a desolvated plasma, and have been corrected by monitoring the 64Zn1H+/64Zn ratio on a pure Zn solution and applying an offline peak subtraction. No Zn hydride interferences were observed on the IsoProbe, suggesting differences in instrument design influence the formation and/or persistence of these species. Matrix-induced interference contributions on the Axiom and IsoProbe show increasing significance from argides (NaAr+, MgAr+, AlAr+) to oxide/hydroxide (TiO+, TiOH+, VO+, VOH+, CrO+, CrOH+) to double-charged species (Ba2+, Ce2+). Switching from solution nebulisation to a desolvated plasma enhances argide and double-charge species, and concurrently depresses oxides and hydroxides, reflecting changing conditions within the ICP-source. These results highlight the importance of removing problematic matrix components prior to Cu and Zn MC-ICP-MS isotope ratio measurements.

Fe isotope variations in natural materials measured using high mass resolution multiple collector ICPMS.

We present the first measurements of Fe isotope variations in chemically purified natural samples using high mass resolution multiple-collector inductively coupled plasma source mass spectrometry (MC-ICPMS). High mass resolution allows polyatomic interferences at Fe masses to be resolved (especially, (40)Ar(14)N(+), (40)Ar(16)O(+), and (40)Ar(16)OH(+)). Simultaneous detection of Fe isotope ion beams using multiple Faraday collectors facilitates high-precision isotope ratio measurements. Fe in basalt and paleosol samples was extracted and purified using a simple, single-stage anion chemistry procedure. A Cu "element spike" was used as an internal standard to correct for variations in mass bias. Using this procedure, we obtained data with an external precision of 0.03-0.11 per thousand and 0.04-0.15 per thousand for delta(56/54)Fe and delta(57/54)Fe, respectively (2sigma). Use of Cu was necessary for such reproducibility, presumably because of subtle effects of residual sample matrix on mass bias. These findings demonstrate the utility of high-resolution MC-ICPMS for high-precision Fe isotope analysis in geologic and other natural materials. They also highlight the importance of internal monitoring of mass bias, particularly when using routine methods for Fe extraction and purification.

High precision isotope ratio measurements of mercury isotopes in cinnabar ores using multi-collector inductively coupled plasma mass spectrometry.

Variations in Hg isotope ratios in cinnabar ores obtained from different countries were detected by high precision isotope ratio measurements using multi-collector inductively coupled mass spectrometry (MC-ICP-MS). Values of delta198/202Hg varied from 0.0-1.3 percent per thousand relative to a NIST SRM 1641d Hg solution. The typical external uncertainty of the delta values was 0.06 to 0.26 percent per thousand. Hg was introduced into the plasma as elemental Hg after reduction by sodium borohydride. A significant fractionation of lead isotopes was observed during the simultaneous generation of lead hydride, preventing normalization of the Hg isotope ratios using the measured 208/206Pb ratio. Hg ratios were instead corrected employing the simultaneously measured 205/203T1 ratio. Using a 10 ng ml(-1) Hg solution and 10 min of sampling, introducing 60 ng of Hg, the internal precision of the isotope ratio measurements was as low as 14 ppm. Absolute Hg ratios deviated from the representative IUPAC values by approximately 0.2% per u. This observation is explained by the inadequacy of the exponential law to correct for mass bias in MC-ICP-MS measurements. In the absence of a precisely characterized Hg isotope ratio standard, we were not able to determine unambiguously the absolute Hg ratios of the ore samples, highlighting the urgent need for certified standard materials.

Determination of 236U/238U isotope ratio in contaminated environmental samples using different ICP-MS instruments

This paper considers use of the 236U isotope to monitor the spent uranium from nuclear fallout using inductively coupled plasma mass spectrometry (ICP-MS) in soil samples collected in the vicinity of the Chernobyl Nuclear Power Plant (NPP). Sector field ICP-MS (ICP-SFMS) and quadrupole based ICP-MS without and with hexapole collision cell (ICP-CC-MS) were used for uranium isotope analysis. In addition, a multiple ion collector ICP-MS (MC-ICP-MS) was used for high-precision isotope ratio measurements. A 238U+ ion sensitivity of 18 GHz ppm−1, 12.4 GHz ppm−1 and 16 GHz ppm−1, respectively, was observed in ICP-SFMS, ICP-CC-MS and MC-ICP-MS with ultrasonic nebulizer. An absolute sensitivity of 3600 counts fg−1 was achieved for uranium by using a direct injection high efficiency nebulizer for solution introduction in ICP-SFMS. The detection limit for 236U was in the fg g−1 range and abundance ratio sensitivity for 236U/238U was 5 × 10−6, 3 × 10−7, 6 × 10−7, and less than 3 × 10−7 in ICP-SFMS, MC-ICP-MS, quadrupole ICP-MS and ICP-CC-MS at mass resolution m/Δm = 300, respectively. Interlaboratory comparison yielded a good accuracy (0.4–1.6%) of 236U/238U isotope ratios ranging from 1.5 × 10−3 to 3.2 × 10−4 measured in samples containing 100 ng of uranium. The 236U/238U isotope ratios and spent uranium fraction were determined in Chernobyl soil samples using single ion detector ICP-MS and multiple ion collector ICP-MS (MC-ICP-MS). In comparison to 235U/238U isotope ratio, the 236U/238U isotope ratio provided more sensitive and accurate determination of the portion of spent uranium from Chernobyl NPP in spent/natural uranium mixture in soil samples down to 0.1%. The concentration of Chernobyl spent uranium in upper 0–10 cm soil layers in investigated areas in the vicinity of Chernobyl NPP amounts to 2.4 × 10−9 g g−1 to 8.1 × 10−7 g g−1 depending mainly on the distance to the Chernobyl reactor.

Sensitive detection of methane and nitrous oxide isotopomers using a continuous wave quantum cascade laser

A continuous wave quantum cascade laser (QCL), operating near 8.1 μm, was used for wavelength modulation spectroscopy of methane (CH4) and nitrous oxide (N2O) stable isotopes. Several rotational transitions of 14N216O, 15N14N16O, 14N218O, 14N217O, 13CH4 and 12CH4 fundamental bands were detected. The noise-equivalent absorbance was measured to be less than 10-5 in a 1-Hz bandwidth. A characterization of the laser source was also performed. The use of a QCL spectrometer for high-precision isotope ratio measurements is discussed.

Correction of instrumentally produced mass fractionation during isotopic analysis of fe by thermal ionization mass spectrometry

High-precision (∼0.015%/mass) isotope ratio measurements of Fe may be obtained by using magnetic-sector thermal ionization mass spectrometry (TIMS), where rigorous correction of instrumentally produced mass fractionation can be made. Such corrections are best done by using a double-spike approach, which was first introduced several decades ago. However, previous derivations do not lend themselves to the high-precision isotope analysis that modern TIMS instruments are capable of because of various assumptions of mass fractionation laws or constant atomic weights. Moreover, some of these previous approaches took iterative approaches to the calculation, and none presented detailed error propagations. Here we present a completely general derivation to the double-spike approach that may be used for any appropriate isotope system and is applicable to the mass fractionation laws that are known to occur in TIMS. In addition, we present an assessment of error propagation as a function of algorithm and spike isotope composition. This approach has produced the highest precision Fe isotope ratio measurements yet reported, on the order of ±0.2 to 0.3 per mil for the 54Fe/ 56Fe ratio, that correct for instrumentally produced mass fractionation and yet retain natural, mass-dependent isotopic variations in samples.

Precise Determination of Cadmium, Indium and Tellurium Using Multiple Collector ICP‐MS

New sample preparation and ion‐exchange separation methods as well as instrumental measurement protocols were established for the determination of trace‐level Cd, In, and Te concentrations in geological materials by isotope‐dilution mass spectrometry. High precision isotope ratio measurements were performed with a multiple collector inductively coupled plasma‐mass spectrometer (MC‐ICP‐MS). The mass biases incurred for In and Te were corrected by adding and monitoring Pd and Sb standard solutions, respectively. Mass fractionation of Cd was corrected by using the mass fractionation factor calculated from the measurement of a standard solution. The measurement precision was better than 1 % for Cd, In and Te. Detection limits were &lt; 1 ng g‐1 for Cd, &lt; 0.02 ng g‐1 for In and Te. Using these new analytical techniques, the concentrations of Cd, In and Te were determined in six international geological reference materials. Concentrations could be reproduced within 3% for Cd, 4% for In and 10% for Te. Sample heterogeneity and volatility problems might have been the reason for the relatively large differences between Te replicates. Our results displayed excellent reproducibility compared with those of other techniques and agree well with data from previously published recommended values.