Multi-collector Inductively Coupled Plasma Mass Spectrometry Research Articles

High-Precision (MC-ICPMS) Isotope Ratio Analysis Reveals Contrasting Sources of Elevated Blood Lead Levels of an Adult with Retained Bullet Fragments, and of His Child, in Milwaukee, Wisconsin.

Exposure to the neurotoxic element lead (Pb) continues to be a major human health concern, particularly for children in US urban settings, and the need for robust tools for assessment of exposure sources has never been greater. The latest generation of multicollector inductively coupled plasma mass spectrometry (MC-ICPMS) instrumentation offers the capability of using Pb isotopic signatures as a tool for environmental source tracking in public health. We present a case where MC-ICPMS was applied to isotopically resolve Pb sources in human clinical samples. An adult male and his child residing in Milwaukee, Wisconsin, presented to care in August 2015 with elevated blood lead levels (BLLs) (>200μg/dL for the adult and 10μg/dL for the child). The adult subject is a gunshot victim who had multiple bullet fragments embedded in soft tissue of his thigh for approximately 10years. This study compared the high-precision isotopic fingerprints (<1‰ 2σ external precision) of Pb in the adult's and child's whole blood (WB) to the following possible Pb sources: a surgically extracted bullet fragment, household paint samples and tap water, and a Pb water-distribution pipe removed from servicing a house in the same neighborhood. Pb in the bullet and adult WB were nearly isotopically indistinguishable (matching within 0.05-0.56‰), indicating that bullet fragments embedded in soft tissue could be the cause of both acute and chronic elevated blood Pb levels. Among other sources investigated, no single source dominated the child's exposure profile as reflected in the elevated BLL.

Monazite RW-1: a homogenous natural reference material for SIMS U–Pb and Th–Pb isotopic analysis

Well-characterized matrix-matched natural mineral references of known age are an important prerequisite for SIMS (secondary ion mass spectrometry) U–Th–Pb dating. We have characterized RW-1, a 44 g yellowish-brown single monazite specimen from a Norwegian pegmatite as an excellent hi-Th reference material for secondary ion mass spectrometric U–Th–Pb dating. A total of 206 secondary ion mass spectrometric analyses over six analytical sessions were performed on different monazite fragments of RW-1. The analyses resulted in 207Pb-based common lead corrected 206Pb/238U ages and Th–Pb ages with overall 2 % (2 SD = standard deviation) variations, indicating the good U–Th–Pb system homogeneity. The homogeneity of Th content of 11.8 ± 1.0 wt% (2 SD) and Th/U of 42 ± 3 (2 SD) make this crystal also a good compositional reference material. We used the combined ID–TIMS(Pb)/ID–MC–ICP–MS(U) technique (i.e. isotope dilution thermal ionization mass spectrometry for Pb, and isotope dilution multi-collector inductively-coupled plasma mass spectrometry for U) to determine U–Pb ages of the monazite samples studied. The mean 207Pb/235U age of 904.15 ± 0.26 Ma (95 % confidence level) is recommended as the best estimate crystallization age for RW-1 monazite. Considering that the most commonly distributed U–Pb monazite reference materials have rather low ThO2, we suggest that this RW-1 monazite with its ThO2 of 13.5 wt% is a suitable reference material providing investigators more confidence when dating high-Th monazite unknowns.

Evaluation of sulfur isotopic enrichment of urine metabolites for the differentiation of healthy and prostate cancer mice after the administration of 34S labelled yeast

Sulfur isotopic enrichment of urine metabolites in healthy and prostate cancer mice using 34S enriched yeast and High Performance Liquid Chromatography coupled to Multicollector Inductively Coupled Plasma Mass Spectrometry (HPLC-MC-ICP-MS) has been evaluated. A 30 weeks experiment (since the eleventh to the fortieth week of life) was carried out collecting the urine of three healthy mice and three transgenic mice with prostate cancer during 24h after a single oral administration of a 34S enriched yeast slurry. The isotopic enrichment of different sulphur metabolites was monitored by coupling a C18 reverse phase HPLC column with a multicollector ICP-MS using a membrane desolvating system. Quantification of sulfur in the chromatographic peaks was carried out by post-column isotope dilution using a 33S enriched spike. Differences between the 34S enrichment in the urine metabolites of healthy and prostate cancer mice were found from the beginning of the disease. Both populations could be differentiated using a principal component analysis (PCA). Finally, 7 unknown mice were correctly classified in each population using a linear discriminant analysis.

Precise Analysis of Gallium Isotopic Composition by MC-ICP-MS.

Though an isotope approach could be beneficial for better understanding the biogeochemical cycle of gallium (Ga), an analogue of the monoisotopic element aluminum (Al), the geochemistry of Ga isotopes has not been widely elaborated. We developed a two-step method for purifying Ga from geological (biological) samples for precise measurement of Ga isotope ratio using multicollector inductively coupled plasma mass spectrometry (MC-ICP-MS). Ga was thoroughly separated from other matrix elements using two chromatographic columns loaded with AG 1-X4 and Ln-spec resin, respectively. The separation method was carefully calibrated using both synthetic and natural samples and validated by assessing the extraction yield (99.8 ± 0.8%, 2SD, n = 23) and the reproducibility (2SD uncertainty better than 0.05‰, n = 116) of the measured isotopic ratio (expressed as δ71Ga). The validation of the whole protocol, together with instrumental analysis, was confirmed by the investigation of the matrix effect, the result of a standard addition experiment, and the comparison of Ga isotope measurement on two mass spectrometers-Nu Plasma II and Neptune Plus. Although the measurements using the sample-standard bracketing (SSB) correction method on both instruments resulted in identical δ71Ga values for reference materials, the modified empirical external normalization (MEEN) method gave relatively better precision compared to SSB on Neptune. Our preliminary results showed large variation of δ71Ga (up to 1.83‰) for 10 standards, with higher values in industrially produced materials, implying potential application of Ga isotopes.

Development of routines for simultaneous in situ chemical composition and stable Si isotope ratio analysis by femtosecond laser ablation inductively coupled plasma mass spectrometry

Stable metal (e.g. Li, Mg, Ca, Fe, Cu, Zn, and Mo) and metalloid (B, Si, Ge) isotope ratio systems have emerged as geochemical tracers to fingerprint distinct physicochemical reactions. These systems are relevant to many Earth Science questions. The benefit of in situ microscale analysis using laser ablation (LA) over bulk sample analysis is to use the spatial context of different phases in the solid sample to disclose the processes that govern their chemical and isotopic compositions. However, there is a lack of in situ analytical routines to obtain a samples' stable isotope ratio together with its chemical composition. Here, we evaluate two novel analytical routines for the simultaneous determination of the chemical and Si stable isotope composition (δ30Si) on the micrometre scale in geological samples. In both routines, multicollector inductively coupled plasma mass spectrometry (MC-ICP-MS) is combined with femtosecond-LA, where stable isotope ratios are corrected for mass bias using standard-sample-bracketing with matrix-independent calibration. The first method is based on laser ablation split stream (LASS), where the laser aerosol is split and introduced simultaneously into both the MC-ICP-MS and a quadrupole ICP-MS. The second method is based on optical emission spectroscopy using direct observation of the MC-ICP-MS plasma (LA-MC-ICP-MS|OES). Both methods are evaluated using international geological reference materials. Accurate and precise Si isotope ratios were obtained with an uncertainty typically better than 0.23‰, 2SD, δ30Si. With both methods major element concentrations (e.g., Na, Al, Si, Mg, Ca) can be simultaneously determined. However, LASS-ICP-MS is superior over LA-MC-ICP-MS|OES, which is limited by its lower sensitivity. Moreover, LASS-ICP-MS offers trace element analysis down to the μg g−1-range for more than 28 elements due to lower limits of detection, and with typical uncertainties better than 15%. For in situ simultaneous stable isotope measurement and chemical composition analysis LASS-ICP-MS in combination with MC-ICP-MS is the method of choice.

Mass Spectrometric Investigation of Silicon Extremely Enriched in (28)Si: From (28)SiF4 (Gas Phase IRMS) to (28)Si Crystals (MC-ICP-MS).

A new generation of silicon crystals even further enriched in (28)Si (x((28)Si) > 0.999 98 mol/mol), recently produced by companies and institutes in Russia within the framework of a project initiated by PTB, were investigated with respect to their isotopic composition and molar mass M(Si). A modified isotope dilution mass spectrometric (IDMS) method treating the silicon as the matrix containing a so-called virtual element (VE) existing of the isotopes (29)Si and (30)Si solely and high resolution multicollector inductively coupled plasma mass spectrometry (MC-ICP-MS) were applied in combination. This method succeeds also when examining the new materials holding merely trace amounts of (29)Si (x((29)Si) ≈ 5 × 10(-6) mol/mol) and (30)Si (x((30)Si) ≈ 7 × 10(-7) mol/mol) extremely difficult to detect with lowest uncertainty. However, there is a need for validating the enrichment in (28)Si already in the precursor material of the final crystals, silicon tetrafluoride (SiF4) gas prior to crystal production. For that purpose, the isotopic composition of selected SiF4 samples was determined using a multicollector magnetic sector field gas-phase isotope ratio mass spectrometer. Contaminations of SiF4 by natural silicon due to storing and during the isotope ratio mass spectrometry (IRMS) measurements were observed and quantified. The respective MC-ICP-MS measurements of the corresponding crystal samples show-in contrast-several advantages compared to gas phase IRMS. M(Si) of the new crystals were determined to some extent with uncertainties urel(M) < 1 × 10(-9). This study presents a clear dependence of the uncertainty urel(M(Si)) on the degree of enrichment in (28)Si. This leads to a reduction of urel(M(Si)) during the past decade by almost 3 orders of magnitude and thus further reduces the uncertainty of the Avogadro constant NA which is one of the preconditions for the redefinition of the SI unit kilogram.

Iron Transformation Pathways and Redox Micro-Environments in Seafloor Sulfide-Mineral Deposits: Spatially Resolved Fe XAS and δ(57/54)Fe Observations.

Hydrothermal sulfide chimneys located along the global system of oceanic spreading centers are habitats for microbial life during active venting. Hydrothermally extinct, or inactive, sulfide deposits also host microbial communities at globally distributed sites. The main goal of this study is to describe Fe transformation pathways, through precipitation and oxidation-reduction (redox) reactions, and examine transformation products for signatures of biological activity using Fe mineralogy and stable isotope approaches. The study includes active and inactive sulfides from the East Pacific Rise 9°50′N vent field. First, the mineralogy of Fe(III)-bearing precipitates is investigated using microprobe X-ray absorption spectroscopy (μXAS) and X-ray diffraction (μXRD). Second, laser-ablation (LA) and micro-drilling (MD) are used to obtain spatially-resolved Fe stable isotope analysis by multicollector-inductively coupled plasma-mass spectrometry (MC-ICP-MS). Eight Fe-bearing minerals representing three mineralogical classes are present in the samples: oxyhydroxides, secondary phyllosilicates, and sulfides. For Fe oxyhydroxides within chimney walls and layers of Si-rich material, enrichments in both heavy and light Fe isotopes relative to pyrite are observed, yielding a range of δ57Fe values up to 6‰. Overall, several pathways for Fe transformation are observed. Pathway 1 is characterized by precipitation of primary sulfide minerals from Fe(II)aq-rich fluids in zones of mixing between vent fluids and seawater. Pathway 2 is also consistent with zones of mixing but involves precipitation of sulfide minerals from Fe(II)aq generated by Fe(III) reduction. Pathway 3 is direct oxidation of Fe(II) aq from hydrothermal fluids to form Fe(III) precipitates. Finally, Pathway 4 involves oxidative alteration of pre-existing sulfide minerals to form Fe(III). The Fe mineralogy and isotope data do not support or refute a unique biological role in sulfide alteration. The findings reveal a dynamic range of Fe transformation pathways consistent with a continuum of micro-environments having variable redox conditions. These micro-environments likely support redox cycling of Fe and S and are consistent with culture-dependent and -independent assessments of microbial physiology and genetic diversity of hydrothermal sulfide deposits.

Effect of parent body evolution on equilibrium and kinetic isotope fractionation: a combined Ni and Fe isotope study of iron and stony-iron meteorites

Various iron and stony-iron meteorites have been characterized for their Ni and Fe isotopic compositions using multi-collector inductively coupled plasma-mass spectrometry (MC-ICP-MS) after sample digestion and chromatographic separation of the target elements in an attempt to further constrain the planetary differentiation processes that shifted these isotope ratios and to shed light on the formational history and evolution of selected achondrite parent body asteroids. Emphasis was placed on spatially resolved isotopic analysis of iron meteorites, known to be inhomogeneous at the μm to mm scale, and on the isotopic characterization of adjacent metal and silicate phases in main group pallasites (PMG), mesosiderites, and the IIE and IAB complex silicate-bearing iron meteorites. In a 3-isotope plot of 60/58Ni versus62/58Ni, the slope of the best-fitting straight line through the laterally resolved Ni isotope ratio data for iron meteorites reveals kinetically controlled isotope fractionation (βexper=1.981±0.039, 1 SD), predominantly resulting from sub-solidus diffusion (with the fractionation exponent β connecting the isotope fractionation factors, as α62/58=α60/58β). The observed relation between δ56/54Fe and Ir concentration in the metal fractions of PMGs and in IIIAB iron meteorites indicates a dependence of the bulk Fe isotopic composition on the fractional crystallization of an asteroidal metal core. No such fractional crystallization trends were found for the corresponding Ni isotope ratios or for other iron meteorite groups, such as the IIABs. In the case of the IIE and IAB silicate-bearing iron meteorites, the Fe and Ni isotopic signatures potentially reflect the influence of impact processes, as the degree of diffusion-controlled Ni isotope fractionation is closer to that of Fe compared to what is observed for magmatic iron meteorite types. Between the metal and olivine counterparts of pallasites, the Fe and Ni isotopic compositions show clearly resolvable differences, similar in magnitude but opposite in sign (Δ56/54Femet-oliv of +0.178±0.092‰ and Δ60/58Nimet-oliv of −0.212±0.082‰, 2SD). As such, the heavier Fe isotope ratios for the metal (δ56/54Fe=+0.023‰ to +0.247‰) and lighter values for the corresponding olivines (δ56/54Fe=−0.155‰ to −0.075‰) are interpreted to reflect later-stage Fe isotopic re-equilibration between these phases, rather than a pristine record of mantle-core differentiation. In the case of mesosiderites, the similarly lighter Ni and Fe isotopic signatures found for the silicate phase (−0.149‰ to +0.023‰ for δ60/58Ni, −0.214‰ to −0.149‰ for δ56/54Fe) compared to the metal phase (+0.168‰ to +0.191‰ for δ60/58Ni, +0.018‰ to +0.120‰ for δ56/54Fe) likely result from Fe and Ni diffusion. Overall, the Fe and Ni isotopic compositions of iron-rich meteorites reflect multiple, often superimposed, processes of equilibrium or kinetic nature, illustrating convoluted parent body histories and late-stage interaction between early-formed planetesimal reservoirs.

Improving Precision and Accuracy of Isotope Ratios from Short Transient Laser Ablation-Multicollector-Inductively Coupled Plasma Mass Spectrometry Signals: Application to Micrometer-Size Uranium Particles.

The isotope drift encountered on short transient signals measured by multicollector inductively coupled plasma mass spectrometry (MC-ICPMS) is related to differences in detector time responses. Faraday to Faraday and Faraday to ion counter time lags were determined and corrected using VBA data processing based on the synchronization of the isotope signals. The coefficient of determination of the linear fit between the two isotopes was selected as the best criterion to obtain accurate detector time lag. The procedure was applied to the analysis by laser ablation-MC-ICPMS of micrometer sized uranium particles (1-3.5 μm). Linear regression slope (LRS) (one isotope plotted over the other), point-by-point, and integration methods were tested to calculate the (235)U/(238)U and (234)U/(238)U ratios. Relative internal precisions of 0.86 to 1.7% and 1.2 to 2.4% were obtained for (235)U/(238)U and (234)U/(238)U, respectively, using LRS calculation, time lag, and mass bias corrections. A relative external precision of 2.1% was obtained for (235)U/(238)U ratios with good accuracy (relative difference with respect to the reference value below 1%).

Iron isotope investigation of hydrothermal and sedimentary pyrite and their aqueous dissolution products

Oxidative dissolution experiments were carried out on pyrite from multiple petrogenetic environments (hydrothermal, sedimentary, and coal-related nodules) to investigate possible variations in the iron isotopic composition of pyrite and the products of pyrite dissolution. The experimental materials were leached under carefully controlled abiotic conditions, and a subset of leachates and starting materials from these experiments was analyzed for 56Fe/54Fe by multicollector ICP-MS. Bulk pyrite δ56Fe values (relative to IRMM-014) ranged from −0.1 to +1.3‰, with hydrothermal bulk pyrite values <+0.5‰ and those of coal and sedimentary nodular pyrite ≥+0.5‰, higher than most previously measured values for Phanerozoic sedimentary pyrite. We suggest that this reflects precipitation of coal pyrite from a high-δ56Fe continental source, such as Fe derived from dissolution of Fe(III) oxides. This interpretation is consistent with pyrite rare earth element (REE) patterns. This could allow differentiation of Fe contributed from coal- and shale-related pyrite at abandoned mine drainage sites. Leachates from oxidative dissolution of the pyrite at pH=3 yielded, with few exceptions, δ56Fe values equal to or lower than those of the coexisting bulk pyrite, by up to about 1‰. These shifts are consistent in direction (but not magnitude) with equilibrium isotope fractionation predictions from theory, with possible second order effects from isotopic heterogeneity within individual natural pyrite samples.

High‐Precision Measurement of Molybdenum Isotopic Compositions of Selected Geochemical Reference Materials

Here we describe high‐precision molybdenum isotopic composition measurements of geological reference materials, performed using multi‐collector inductively coupled plasma‐mass spectrometry (MC‐ICP‐MS). Purification of Mo for isotopic measurements was achieved by ion exchange chromatography using Bio‐Rad AG® 1‐X8 anion exchange resin. Instrumental mass bias was corrected using 100Mo‐97Mo double spiking techniques. The precision under intermediate measurement conditions (eighteen measurement sessions over 20 months) in terms of δ98/95Mo was 0.10‰ (2s). The measurement output was approximately four times more efficient than previous techniques, with no compromise in precision. The Mo isotopic compositions of seven geochemical reference materials, seawater (IAPSO), manganese nodules (NOD‐P‐1 and NOD‐A‐1), copper‐molybdenum ore (HV‐2), basalt (BCR‐2) and shale (SGR‐1b and SCo‐1), were measured. δ98/95Mo values were obtained for IAPSO (2.25 ± 0.09‰), NOD‐P‐1 (−0.66 ± 0.05‰), NOD‐A‐1 (−0.48 ± 0.05‰), HV‐2 (−0.23 ± 0.10‰), BCR‐2 (0.21 ± 0.07‰), SCo‐1 (−0.24 ± 0.06‰) and SGR‐1b (0.63 ± 0.02‰) by calculating δ98/95Mo relative to NIST SRM 3134 (0.25‰, 2s). The molybdenum isotopic compositions of IAPSO, NOD‐A‐1 and NOD‐P‐1 obtained in this study are within error of the compositions reported previously. Molybdenum isotopic compositions for BCR‐2, SCo‐1 and SGR‐1b are reported for the first time.

Uranium isotope analysis by MC-ICP-MS in sub-ng sized samples

This study describes the multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) method for the determination of n(233U)/n(238U), n(234U)/n(238U), n(235U)/n(238U), and n(236U)/n(238U) isotope ratios in purified uranium solutions.

Vanadium isotope ratio measurements in fruit-bodies of Amanita muscaria

A new method has been developed for precise vanadium isotope ratio measurements by multi-collector inductively coupled plasma mass spectrometry (MC-ICPMS) inAmanita muscaria– a widespread toxic and hallucinogenic mushroom which is also known for its ability to bio-accumulate vanadium.

Effects of mercury and thallium concentrations on high precision determination of mercury isotopic composition by Neptune Plus multiple collector inductively coupled plasma mass spectrometry

Thallium (Tl) has been widely used as an internal standard for mass bias correction during high precision mercury (Hg) isotope ratio measurements using multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS).

On-line separation of strontium from a matrix and determination of the 87Sr/86Sr ratio by Ion Chromatography/Multicollector-ICPMS

In this work a high throughput, robust and sensitive method for the precise isotopic analysis of 87Sr/86Sr by coupling Ion Chromatography (IC) and Multicollector Inductively Coupled Plasma Mass Spectrometry (MC-ICPMS) is presented.

Comprehensive Isotopic and Elemental Analysis of a Multi-Oxide Glass By Multicollector ICP-MS in Isotope Substitution Studies

Multicollector ICP-MS was used to comprehensively analyze different types of isotopically modified glass created to investigate the processes of glass corrosion in the water. Analytical methods were developed for the analyses of synthesized, isotopically modified solid glass and the release of glass constituents upon contact with deionized water. To validate the methods, results from an acid digestion sample of the Analytical Reference Glass showed good agreement when compared to data from multiple prior analyses on the same glass [1]. In this paper, we present the results of the comprehensive analysis of the acid digestion of six types of isotopically modified glass and the release of glass constituents into water corrosion after one year of aqueous corrosion.

Matrix effects and mass bias caused by inorganic acids on boron isotope determination by multi-collector ICP-MS

Matrix effects and mass bias of inorganic acids on boron isotope measurement by MC-ICP-MS have been investigated.

Intra-skeletal calcite in a live-collected Porites sp.: Impact on environmental proxies and potential formation process

Geochemical proxies measured in the carbonate skeleton of tropical coral Porites sp. have commonly been used to reconstruct sea surface temperature (SST) and more recently seawater pH. Nevertheless, both reconstructed SST and pH depend on the preservation state of the skeleton, here made of aragonite; i.e., diagenetic processes and its related effects should be limited. In this study, we report on the impact of the presence of intra-skeletal calcite on the skeleton geochemistry of a live-collected Porites sp. The Porites skeleton preservation state was analyzed using X-ray diffraction and scanning electron microscopy. Sr/Ca, Mg/Ca, U/Ca, Ba/Ca, Li/Mg, and B/Ca ratios were measured at a monthly and yearly resolution using quadrupole ICP-MS and multi-collector ICP-MS. The δ11B signatures and the calcite percentages were acquired at a yearly timescale. The coral colony presents two parts, one with less than 3% calcite (referred to as “no-calcite” skeleton), the other one, corresponding to the skeleton formed during the last 4years of growth, with calcite percentages varying from 13% to 32% (referred to as “with calcite” skeleton). This intra-skeletal calcite replaces partly or completely numerous centers of calcification (COCs). All investigated geochemical tracers are significantly impacted by the presence of calcite. The reconstructed SST decreases by about 0.1°C per calcite-percent as inferred from the Sr/Ca ratio. Such impact reaches up to 0.26°C per calcite-percent for temperature deduced from the Li/Mg ratio. So, less than 5% of such intra-skeletal calcite does not prevent SST reconstructions using Sr/Ca ratio, but the percentage and type of calcite have to be determined before fine SST interpretation. Seawater pH reconstruction inferred from boron isotopes drop by about −0.011 pH-unit per calcite-percent. Such sensitivity to calcite presence is particularly dramatic for fine paleo-pH reconstructions. Here we suggest that after being brought to shallow waters following a cyclone, the studied coral was seasonally subjected to rainfall-related water freshening that could have mimicked a vadose environment like can be encountered on raised fossil coral reefs. Nevertheless, the process of calcite precipitation remains to be determined.

The importance of a Ni correction with ion counter in the double spike analysis of Fe isotope compositions using a 57Fe/58Fe double spike

AbstractWe present a new method capable of measuring iron isotope ratios of igneous materials to high precision by multicollector inductively coupled plasma mass spectrometry (MC‐ICP‐MS) using a 57Fe‐58Fe double spike. After sample purification, near‐baseline signal levels of nickel are still present in the sample solution, acting as an isobaric interference on 58 amu. To correct for the interference, the minor 60Ni isotope is monitored and used to subtract a proportional 58Ni signal from the total 58 amu beam. The 60Ni signal is difficult to precisely measure on the Faraday detector due to Johnson noise occurring at similar magnitude. This noise‐dominated signal is subtracted from the total 58 amu beam, and its error amplified during the double spike correction. Placing the 60Ni beam on an ion counter produces a more precise measurement, resulting in a near‐threefold improvement in δ56Fe reproducibility, from ±0.145‰ when measured on Faraday to 0.052‰. Faraday detectors quantify the 60Ni signal poorly, and fail to discern the transient 20Ne40Ar interference visible on the ion counter, which is likely responsible for poor reproducibility. Another consideration is instrumental stability (defined herein as drift in peak center mass), which affects high‐resolution analyses. Analyses experiencing large drift relative to bracketing standards often yield nonreplicating data. Based on this, we present a quantitative outlier detection method capable of detecting drift‐affected data. After outlier rejection, long‐term precision on individual runs of our secondary standard improves to ±0.046‰. Averaging 3–4 analyses further improves precision to 0.019‰, allowing distinction between ultramafic minerals.

Review of High-Precision Sr Isotope Analyses of Low-Sr Geological Samples

Isotope plays an important role in both tracing and dating in earth science, especially 87Rb-86Sr system. With the development of earth science, whole-rock analysis can’t sufficiently meet the requirements for scientific research and the micro-analysis becomes more and more significant. Laser ablation multi-collector inductively-coupled plasma mass-spectrometry (LA-MC-ICP-MS) has been extensively applied in micro-zone analysis due to its low sample-consumption, high accuracy, in situ and low requirements on matrix, but it is still difficult to accurately measure Sr isotope compositions especially for the samples with high Rb/Sr ratios and low Sr contents as it is restricted by severe quality discrimination and various types of mass spectrum interferences. Consequently, thermal ionization mass-spectrometry (TIMS), as the most accurate and precise method to analyze isotopic ratios, is still the most popular method of analyzing Sr ratios, especially for the samples with low Sr contents. This paper makes a systematic review on the high-precision Sr isotope analyses of low-Sr geological samples, including the micro-sampling technique, ultra-low procedural blank chemical method and TIMS measurement technique. The combination of ultra-low procedural blank and TIMS can be used to perform high-precision micro-analysis of the samples with ng magnitude, which will be undoubtedly an important direction for Rb-Sr geochronology, geochemistry and environmental studies.