Isotopic Analytical Techniques Research Articles

Busting the dust: Evaluating local vs distal sources in Quaternary sediments at Thirlmere Lakes

The Quaternary sediments preserved within the Thirlmere Lakes system, Greater Blue Mountains World Heritage Area, Australia, are an important regional environmental record representing at least the last two interglacials. Understanding the source and evolution of these sediments, both temporally and spatially, is an essential component of the site's reconstruction. In this study, we evaluate this question using physical, mineralogical, elemental, and isotopic analytical techniques. Four distinct lake sediment facies all show bi-modal distributions of coarse sand and clay to fine silts, representing various mixtures of catchment Hawkesbury Sandstone and Ashfield Shale. Clays are predominantly kaolinite-dickite, however, the 7 Å dehydrated form of halloysite is prominent in an orange-yellow oxidised lake facies unit. The relative distribution and concentration of rare earth elements, including yttrium (REY), is heterogeneous across all the lake facies, varying between both lakes and with depth. This variability suggests a geochemical signature reflecting a combination of mixed sources and secondary mineral precipitation, driven by catchment geomorphology and specific site conditions. Slightly positive Ce anomalies in the oxidised lake facies, combined with the greater halloysite representation, represents a period of dry conditions and sub-aerial exposure. Evaluation of catchment, regional and continental REY ratios, Eu anomalies and εNd data implies a predominant internal catchment source signature, with any external contributions restricted to the local Bringelly Shale and the immediate south-eastern Australia, including the Murray River Basin. Geochemical and isotopic values for these proposed internal and external sediment sources predicts that an aeolian source from outside the immediate catchment represents a maximum of 30% of the fine-grained sediment fraction.

A passive method for sampling water in the soil-plant-atmosphere continuum for stable hydrogen and oxygen isotope analyses.

Hydrogen and oxygen isotopes in water molecules are powerful tools to constrain the dynamics of water cycling within the soil-plant-atmosphere continuum (SPAC). However, the recovery of water from the SPAC requires logistical arrangements and implementation of different time- and cost-consuming techniques in either the field or the laboratory. We developed a passive method to sample water from the three compartments of the SPAC by using a hygroscopic salt of a high water absorbance capacity (CaCl2 ). This method allows either H2 O(V) -H2 O(L) isotope equilibration in the case of infinite water reservoir (atmospheric water vapor (WV)) or quantitative absorption of water from a finite water reservoir (e.g. soil and plants). The water absorbed by CaCl2 was distilled first and subsequently processed for hydrogen and triple oxygen isotope mass spectrometry analyses. The distillation step can be bypassed when employing isotope analytical techniques that are based on equilibration. Our experiments show that anhydrous CaCl2 absorbs WV of 210 ± 6% and 130 ± 6% of its dry weight from an infinite WV reservoir at relative humidity of 60% and 30%, respectively. Chemical and isotope equilibrations between WV and absorbed water were attained within 3 days at room temperature, enabling the back-calculation of the isotope composition of atmospheric WV. Preliminary experiments to extract water from plant and sand (i.e. finite WV reservoir) demonstrate a quasi-complete recovery of water in these matrices without significant isotope fractionation. The reproducibility of our method is better than 1.6‰, 0.32‰, 0.17‰ and 6‰ per meg for δ2 H, δ18 O, δ17 O and 17 O-excess. The CaCl2 -H2 O absorption (passive) method requires very limited logistics in the field facilitating spatial and temporal water vapor/water sampling from atmosphere and soil at low resolution (i.e. average of 3-5 days). Moreover, it allows high sample throughput for the extraction of plant water in the laboratory. The reproducibility of this method is similar to the analytical uncertainty in mass spectrometry analyses.

Thorium isotope evidence for glacial–interglacial dust storminess and productivity in the North Pacific gyre

The flux of dust deposition to the ocean and its impact on marine biological productivity are outstanding issues of the Earth’s climate system. The North Pacific gyre (NPG) is the Earth’s largest ecosystem and is important for marine nitrogen fixation, which is sensitive to Asian dust-regulated surface nutrient stoichiometry. Meanwhile, it is one of the least studied regions in the global ocean during the late Pleistocene, because of the extremely slow sediment accumulation and lack of biological material preservation. 232Th and 230Th concentrations recorded by hydrogenetic ferromanganese crusts in the deep NPG provide a novel and quantitative proxy of dust deposition and export productivity in this region. For this purpose, we have established an in situ U–Th isotope analytical technique on hydrogenetic ferromanganese crusts collected from the deep NPG. Iron, Mn, and Co of our samples have also been analyzed to constrain the impact of dust dissolution on the Fe geochemical cycle. Remarkably, variability of the 232Th-based dust flux over the last ∼900 ky exhibits a striking resemblance to grain-size records of the Chinese loess deposits and sea-level reconstructions but clearly decouples from the global temperature evolution. On orbital time scales, dust storms over the NPG are apparently sensitive to effects related to continental ice sheet sizes but decoupled from major global cooling during the early glaciation. While our 232Th data indicate a 2- to 3-fold variability of glacial–interglacial dust flux, scavenging of Fe, Mn, and Co in the deep NPG is much less variable through the late Pleistocene. We suggest that variable dust fluxes have a limited impact on the inventory of dissolved Fe in the deep waters of NPG, even though the scavenging of Fe has likely been regulated by glacial–interglacial paleoceanography. The paired 230Th-scavenging-based biological productivity tracks gyre sea surface temperature rather than dust flux during the last glacial cycle. We observe no correlation between dust flux and export productivity in the NPG, indicating that dust-derived Fe is not the productivity-limiting factor on orbital time scales in this region. Instead, these results imply that changes in gyre mixing and mode water formation might have led to increased supply of phosphorous and thus enhanced glacial biological carbon sequestration, with potentially stronger nitrogen fixation under higher eolian input.

Extracting daily isotopic records on fish otolith (Trachurus japonicus) by combining micro-milling and micro-scale isotopic analysis(MICAL-CF-IRMS).

The recent progress in micro-scale isotopic analytical techniques for otoliths has enabled the reconstruction of the experienced water temperature history of fish in every few days resolution using the stable oxygen isotope ratio (δ18 O) of otoliths. We aimed to improve those techniques and extract the daily δ18 O records of otoliths formed during the juvenile period. Growth rings were formed daily in fish otoliths. We precisely distinguished the daily rings in otoliths of Japanese jack mackerel Trachurus japonicus, and milled them along daily growth rings using a high-spatial resolution micromilling system (Geomill326). Then, we determined the stable carbon and oxygen (δ13 C, δ18 O) isotopic compositions using a high-precision micro-scale isotopic analytical system (MICAL3c with IsoPrime 100). We successfully milled each daily ring with width ranging from 14.0 to 62.9μm (average 27.0μm) during the high growth period (30-70 days after hatching), and determined the isotopic compositions of otolith aragonite. Our improved micro-scale analytical method is the first to determine the daily δ18 O history of fish otoliths. By using our method together with the δ18 O - water temperature equation, the daily history of experienced water temperature can be elucidated. Our high-resolution milling and analytical technique can also be applied to high-resolution isotope analysis for stalactites, clams, and corals.

Short-Lived Nuclides in the Early Solar System: Abundances, Origins, and Applications

Several short-lived radionuclides (SLRs) were present in the first few million years of Solar System history. Their abundances have profound impact on the timing of stellar nucleosynthesis events prior to Solar System formation, chronology of events in the early Solar System, early solar activity, heating of early-formed planetesimals, and chronology of planet formation. Isotopic analytical techniques have undergone dramatic improvements in the past decade, leading to tighter constraints on the levels of SLRs in the early Solar System and on the use of these nuclides for detailed chronological studies. This review emphasizes the abundances of SLRs when the Solar System formed and how we know them, and briefly discusses the origins of these nuclides and applications in planetary science.

Lithium Isotope Measurement Using Laser-Induced Breakdown Spectroscopy and Chemometrics.

Laser-induced breakdown spectroscopy (LIBS) is a technique capable of portable, quantitative elemental analysis; however, quantitative isotopic determination of samples in situ has not yet been demonstrated. This research demonstrates the ability of LIBS to quantitatively determine concentrations of 6Li in solid samples of lithium hydroxide monohydrate in a nominally 40 mTorr argon environment using chemometrics. Three chemometric analysis techniques (principal component regression, partial least squares regression, and neural networks analysis) are applied to spectra collected using a spectrometer with modest resolving power (λ/Δλ ≈ 27 000). This analysis suggests that bulk lithium isotopic assay can be determined using LIBS to within a 95% confidence interval in minutes to an hour for enrichment levels ranging from 3% to 85%. This has direct applications for the nuclear safeguards and geological exploration communities and others that desire a portable, stable isotope analytical technique. Additionally, isotope-specific self-absorption of atomic emission in a laser-produced plasma is observed for the first time.

Sensitive detection of atmospheric N2O isotopomers using a quantum cascade laser based spectrometer

Stable isotope analytical techniques have a crucial role to play in the study of atmospheric pollutant and trace gas sources, sinks and transport processes. Quantum cascade laser absorption spectroscopy (QCLAS) allows the site-selective and high-precision analysis of many isotopic species at trace levels, yet not sensitive enough for atmospheric N2O mixing ratios. In this study, a quantum cascade laser based spectrometer combining with a liquid nitrogen-free preconcentration unit was developed to demonstrate the applicability of high sensitivity and high precision measurement of atmospheric N2O isotopomers. Primary laboratory tests have been performed for simultaneous determination of the mixing ratios of the most abundant nitrous oxide isotopic species: 14N15N16O, 15N14N16O and 14N216O. The experiment results showed that site-selective 15N/14N can be measured with the precision of 0.59‰ with an optimal averaging time of 258 s at 100 ppm. Details of spectral absorption line pairs selection and N2O adsorption/desorption processes are also discussed.

Combining Denitrifying Bacteria and Laser Spectroscopy for Isotopic Analyses (δ(15)N, δ(18)O) of Dissolved Nitrate.

We present a novel approach for nitrogen (δ(15)N) and oxygen (δ(18)O) isotopic analysis of nitrate in water based on the isotopic analysis of N2O produced from the conversion of NO3(-) by cultured denitrifying bacteria and off-axis integrated cavity output spectroscopy (OA-ICOS). The headspace N2O was manually injected into an OA-ICOS isotopic N2O laser analyzer through a syringe septum port. Sample analysis time was ∼300 s. The use of OA-ICOS technology yields accurate and precise δ(15)N and δ(18)O results for dissolved nitrate samples when nonlinearity issues are considered. This new isotope analytical technique thus improves the isotopic analysis of nitrates by (i) providing accurate measurements of δ(15)N and δ(18)O without preconcentration, (ii) eliminating interferences by other gas substances (i.e., H2O and CO2), and (iii) reducing extensive maintenance and costs of isotope ratio mass spectrometers (IRMS). This approach will greatly streamline the identification and quantification of nitrate sources in aquatic systems.

Drivers of atmospheric nitrate processing and export in forested catchments

AbstractIncreased deposition of reactive atmospheric N has resulted in the nitrogen saturation of many forested catchments worldwide. Isotope‐based studies from multiple forest sites report low proportions (mean = ∼10%) of unprocessed atmospheric nitrate in streams during baseflow, regardless of N deposition or nitrate export rates. Given similar proportions of atmospheric nitrate in baseflow across a variety of sites and forest types, it is important to address the postdepositional drivers and processes that affect atmospheric nitrate transport and fate within catchments. In a meta‐analysis of stable isotope‐based studies, we examined the influence of methodological, biological, and hydrologic drivers on the export of atmospheric nitrate from forests. The δ18O‐ values in stream waters may increase, decrease, or not change with increasing discharge during stormflow conditions, and δ18O‐ values are generally higher in stormflow than baseflow. However, δ18O‐ values tended to increase with increasing baseflow discharge at all sites examined. To explain these differences, we present a conceptual model of hydrologic flowpath characteristics (e.g., saturation overland flow versus subsurface stormflow) that considers the influence of topography on landscape‐stream hydrologic connectivity and delivery of unprocessed atmospheric nitrate to streams. Methodological biases resulting from differences in sampling frequency and stable isotope analytical techniques may further influence the perceived degree of unprocessed atmospheric nitrate export. Synthesis of results from numerous isotope‐based studies shows that small proportions of unprocessed atmospheric nitrate are common in baseflow. However, hydrologic, topographic, and methodological factors are important drivers of actual or perceived elevated contributions of unprocessed atmospheric nitrate to streams.

Trophodynamics and organic matter assimilation pathways in the northeast Chukchi Sea, Alaska

We analyzed trophic linkages in the northeast Chukchi Sea shelf based on the stable carbon and nitrogen isotopic analysis of 39 species collected in 2009 and 2010. To decipher organic matter assimilation pathways, benthic fauna were first categorized into nine trophic guilds based on their physical location in the seabed (epibenthic, surface, or subsurface), feeding mode (suspension feeder, deposit feeder, predator, or scavenger), and food source (suspended particulate organic matter, phytoplankton, zooplankton, sediment, microflora, meiofauna, or macrofauna). A discriminant function analysis (DFA) determined that feeding modes were predicted by stable isotope values at an overall classification success rate of 42%, although classification success of each individual guild varied from 0 to 66%. In some instances, stable isotopes classified trophic guilds incorrectly more often than correctly, suggesting high trophic redundancy in the system. A striking pattern was observed where the δ13C values of individuals in some trophic guilds, ranging from about −23 to −17‰, were substantially more 13C-enriched than representative end-members, which includes phytoplankton (−24.0‰), suspended particulate organic matter (−24.3‰), and bulk sediment organic matter (−23.3‰). In contrast, near-seafloor suspended particulate organic matter was significantly 13C-enriched compared to suspended particulate organic matter of near surface waters (p<0.05), and bulk sedimentary organic matter was more 13C-enriched than overlying phytoplankton at seven of 10 stations. This suggests the presence of an unmeasured 13C-enriched end-member that is a product of biogeochemical alteration and reworking by the sediment microbial community. Although the microbial community is difficult to quantify using bulk stable isotope analytical techniques, these results indicate it cannot be overlooked as a critical component and avenue through which large amounts of reduced carbon are assimilated by a rich and diverse arctic shelf food web.

A precise analytical method for bromine stable isotopes in natural waters by GasBench II-IRMS

A precise analytical methodology for bromine stable isotope was established by GasBench II-IRMS. The bromine isotope analytical technique consists of two key links: the separation and purification of bromine and mass spectrometry of bromine stable isotope. The separation and purification of bromine aims at extracting bromine from natural waters containing a mass of chlorine and then precipitating bromide in form of silver bromide. By reacting with methyl iodide, silver bromide is converted to methyl bromide, which is analyzed by GasBench II-IRMS next. GasBench II-IRMS is mainly composed of a multipurpose online gas preparation device (GasBench II) containing CP-PoraPlot-Q chromatographic column and a gas stable isotope ratio mass spectrometer (MAT253). By mass spectrometry, the internal precision and external precision for this method can be reached at better than ±0.03‰ (n=12) and ±0.06‰ (n=8) with analysis time of 15min,which achieved the international top level. Applying this method to measure bromine isotope compositions of typical geothermal groundwater, oilfield water, saline groundwater and salt lake water in China, different fractionation effect between bromine and chlorine and remarkable bromine isotope fractionation effect from different sources and evolutionary processes were observed.

Practical considerations for the use of pollen δ13C value as a paleoclimate indicator

Workers have shown a correlation between temperature and the pollen δ(13)C value, and therefore suggested using pollen δ(13)C values to reconstruct paleotemperature. To evaluate the potential for pollen δ(13)C values to be used as a paleotemperature proxy, it is essential to quantify the variability in pollen δ(13)C values and to evaluate the effect of temperature on pollen δ(13)C values, in isolation, under controlled environmental conditions. Pollen was isolated from 146 Hibiscus flowers from 26 plants within a single climate environment to evaluate isotopic variability in pollen δ(13)C values. The nearest leaf (n = 82) and flower phloem (n = 30) were also sampled to measure the δ(13)C variability in carbon providing the raw material for new growth. To evaluate the correlation between temperature and pollen δ(13)C values, we isolated pollen from 89 Brassica rapa plants grown in controlled growth chambers with temperatures ranging from 17 to 32°C. The range in pollen δ(13)C values collected from different flowers on the same Hibiscus plant was large (average = 1.6‰), and could be as much as 3.2‰. This amount of variability was similar to that seen between flower-adjacent leaves, and phloem extracted from styles of individual flowers. In controlled growth chamber experiments, we saw no correlation between temperature and the pollen (R(2) = 0.005) or leaf (R(2) = 0.10) δ(13)C values. We measured large variability in pollen δ(13)C values. When temperature was isolated from other environmental parameters, temperature did not correlate with the pollen δ(13)C value. These results complicate the supposed relationship between temperature and pollen δ(13)C values and caution against using nanogram isotope analytical techniques for characterizing whole-plant individuals.

Error propagation in normalization of stable isotope data: a Monte Carlo analysis

A higher analytical precision of a stable isotope ratio mass spectrometer does not automatically guarantee accurate determination of the true isotope composition (delta-value) of samples, since estimates of true delta-values are obtained from the normalization of raw isotope data. We performed both Monte Carlo simulations and laboratory experiments to investigate aspects of error propagation during the normalization of carbon stable isotope data. We found that increasing both the number of different reference standards and the number of repetitions of each of these standards reduces the normalization error. A 50% reduction in the normalization error can be achieved over the two-point normalization by either analyzing two standards four times each, or four standards two times each. If the true delta-value of a sample is approximately known a priori, the normalization error may then be reduced through a targeted choice of locally optimal standards. However, the difference in improvement is minimal and, therefore, a more practical strategy is to use two or more standards covering the whole stable isotope scale. The selection of different sets of standards by different laboratories or for different batches of samples in the same laboratory may lead to significant differences in the normalized delta-values of the same samples, leading to inconsistent results. Hence, the same set of standards should always be used for a particular element and a particular stable isotope analytical technique.

Application of the stable-isotope system to the study of sources and fate of Hg in the environment: A review

With the improvement of analytical methods and the development of multiple-collector inductively coupled plasma-mass spectrometry (MC-ICP/MS), research on non-traditional stable isotope (Cu, Zn, Fe, Se, Mo, Cr, Hg) in geochemistry has made tremendous progress in the past decade. Recent studies have demonstrated that both organic and inorganic reactions may cause Hg isotope fractionation, and variations of Hg isotopic composition in the environment have been successfully employed to explain Hg pollution history, Hg sources and tracking Hg pathways in nature. Furthermore, Hg isotopic fractionation studies can be a powerful tool in the calibration of global Hg cycling models. Stable isotope geochemistry of Hg is therefore becoming a new frontier subject in earth sciences. Based on summarizing previous research, this paper outlines the main advances in the study of Hg stable isotopes with particular emphasis placed on a brief explanation of Hg isotope analytical techniques, possible Hg isotope fractionation mechanisms observed in both natural and experimental processes, Hg isotope composition variations in different environmental matrices, and the application prospects of the Hg stable isotopes in environmental geosciences.

Grain-scale iron isotopic distribution of pyrite from Precambrian shallow marine carbonate revealed by a femtosecond laser ablation multicollector ICP-MS technique: Possible proxy for the redox state of ancient seawater

The redox state of Precambrian shallow seas has been linked with material cycle and evolution of the photosynthesis-based ecosystem. Iron is a redox-sensitive element and exists as a soluble Fe(II) species or insoluble Fe(III) species on Earth’s surface. Previous studies have shown that the iron isotopic ratio of marine sedimentary minerals is useful for understanding the ocean redox state, although the redox state of the Archean shallow sea is poorly known. This is partly because the conventional bulk isotope analytical technique has often been used, wherein the iron isotopic record may be dampened by the presence of isotopically different iron-bearing minerals within the same sample. Here we report a microscale iron isotopic ratio of individual pyrite grains in shallow marine stromatolitic carbonates over geological time using a newly developed, near-infrared femtosecond laser ablation multicollector ICP-MS technique (NIR-fs-LA-MC-ICP-MS). We have determined that the grain-scale iron isotopic distribution of pyrite from coeval samples shows a bimodal (2.7 and 2.3 Ga) or unimodal pattern (2.9, 2.6, and 0.7 Ga). In particular, pyrite from the 2.7 Ga Fortescue Group shows a unique bimodal distribution with highly positive (+1.0‰ defined as Type 1) and negative δ 56Fe values (−1.8‰ defined as Type 2). Type 1 and 2 pyrites occasionally occur within different siliceous layers in the same rock specimen. Layer-scale iron isotopic heterogeneity indicates that the iron isotopic ratios of the two types of pyrite are not homogenized by diagenesis after deposition. Some cubic pyrites have a core with a positive δ 56Fe value (1‰) and a rim with a crustal δ 56Fe value (0‰). The observed isotopic zoning suggests that the positive δ 56Fe value is a primary signature at the time of stromatolite formation, while secondary pyrite precipitated during diagenesis. The positive δ 56Fe value of Type 1 and the large iron isotopic difference between Type 1 and 2 (2.8‰.) suggest partial Fe(II) oxidation in the 2.7-Ga shallow sea, i.e., pyritization of 56Fe-enriched ferric oxyhydroxide (Type 1) and 56Fe depleted Fe 2+aq in seawater (Type 2). Type 2 pyrite was probably not produced by microbial iron redox cycling during diagenesis because this scenario requires a higher abundance of pyrite with δ 56Fe of 0‰ than of −1.8‰. Consequently, the degree of Fe(II) oxidation in the 2.7-Ga shallow sea can be estimated by a Fe 2+aq steady-state model. The model calculation shows that half the Fe 2+aq influx was oxidized in the seawater. This implies that O 2 produced by photosynthesis would have been completely consumed by oxidation of the Fe 2+aq influx. Grain-scale iron isotopic distribution of pyrite could be a useful index for reconstructing the redox state of the Archean shallow sea.

Advances in laser-based isotope ratio measurements: selected applications

AbstractSmall molecules exhibit characteristic ro-vibrational transitions in the near- and mid-infrared spectral regions, which are strongly influenced by isotopic substitution. This gift of nature has made it possible to use laser spectroscopy for the accurate analysis of the isotopic composition of gaseous samples. Nowadays, laser spectroscopy is clearly recognized as a valid alternative to isotope ratio mass spectrometry. Laser-based instruments are leaving the research laboratory stage and are being used by a growing number of isotope researchers for significant advances in their own field of research. In this review article, we discuss the current status and new frontiers of research on high-sensitivity and high-precision laser spectroscopy for isotope ratio analyses. Although many of our comments will be generally applicable to laser isotope ratio analyses in molecules of environmental importance, this paper concerns itself primarily with water and carbon dioxide, two molecules that were studied extensively in our respective laboratories. A complete coverage of the field is practically not feasible in the space constraints of this issue, and in any case doomed to fail, considering the large body of work that has appeared ever since the review by Kerstel in 2004 (Handbook of Stable Isotope Analytical Techniques, Chapt. 34, pp. 759–787).

Trace- and rare-earth element geochemistry and Pb–Pb dating of black shales and intercalated Ni–Mo–PGE–Au sulfide ores in Lower Cambrian strata, Yangtze Platform, South China

The Lower Cambrian black shale sequence of the Niutitang Formation in the Yangtze Platform, South China, hosts an extreme metal-enriched sulfide ore bed that shows >10,000 times enrichment in Mo, Ni, Se, Re, Os, As, Hg, and Sb and >1,000 times enrichment in Ag, Au, Pt, and Pd, when compared to average upper continental crust. We report in this paper trace- and rare-earth-element concentrations and Pb–Pb isotope dating for the Ni–Mo–PGE–Au sulfide ores and their host black shales. Both the sulfide ores and their host black shales show similar trace-element distribution patterns with pronounced depletion in Th, Nb, Hf, Zr, and Ti, and extreme enrichment in U, Ni, Mo, and V compared to average upper crust. The high-field-strength elements, such as Zr, Hf, Nb, Ta, Sc, Th, rare-earth elements, Rb, and Ga, show significant inter-element correlations and may have been derived mainly from terrigenous sources. The redox sensitive elements, such as V, Ni, Mo, U, and Mn; base metals, such as Cu, Zn, and Pb; and Sr and Ba may have been derived from mixing of seawater and venting hydrothermal sources. The chondrite-normalized REE patterns, positive Eu and Y anomalies, and high Y/Ho ratios for the Ni–Mo–PGE–Au sulfide ores are also suggestive for their submarine hydrothermal-exhalative origin. A stepwise acid-leaching Pb–Pb isotope analytical technique has been employed for the Niutitang black shales and the Ni–Mo–PGE–Au sulfide ores, and two Pb–Pb isochron ages have been obtained for the black shales (531±24 Ma) and for the Ni–Mo–PGE–Au sulfide ores (521±54 Ma), respectively, which are identical and overlap within uncertainty, and are in good agreement with previously obtained ages for presumed age-equivalent strata.

Development of rapid and precise Pb isotope analytical techniques using MC-ICP-MS and new results for GSJ rock reference samples

A rapid and precise routine Pb isotope analytical technique for rock samples was developed using multiple collector inductively coupled plasma mass spectrometry (MC-ICP-MS). The mass discrimination of the Pb isotope ratios was corrected with the 205Tl/203Tl ratio of a Tl isotope reference material (NIST SRM 997) added to samples. The optimization of the analytical parameters and the minimization of the memory and matrix effects enabled to acquire the Pb isotope data rapidly (three samples per hour) with a reproducibility of 0.01% by consumption of 150 ng Pb per analysis. Repeated analyses of a Pb isotope reference material, NIST SRM 981, gave the average values of 206Pb/204Pb = 16.9308 ± 0.0010, 207Pb/204Pb = 15.4839 ± 0.0011, and 208Pb/204b = 36.6743 ± 0.0030 (2σ).Pb isotope ratios of eleven Geological Survey of Japan rock reference samples were determined using this technique. In anion-exchange chemical separation, complete removal of Hg and Tl from the Pb fraction was confirmed. It was revealed that the Tl-normalization minimized the matrix effects caused by remaining impurities and medium, and the reproducibility of seven independent analyses of JB-2 was comparable to that of NIST SRM 981. Pb isotope ratios obtained for the rock reference samples showed a good agreement with those given previously.

Isotopic and nuclear analytical techniques for health and environment.

Isotopic and nuclear analytical techniques for health and environment.

Strontium, Neodymium and Lead Isotope Analyses of NIST Glass Certified Reference Materials: SRM 610, 612, 614

The NIST glass certified reference materials, SRM 610‐617, have been widely adopted by the geological community as calibration samples for a variety of in situ trace element analytical techniques. There is now an urgent requirement for similar reference materials for in situ isotopic analytical techniques. We have analysed SRM 610, 612 and 614 for their Pb, Sr and Nd isotopic compositions using thermal ionisation mass spectrometry. Large differences in isotopic composition were observed between each CRM, suggesting a significant trace element content in the initial starting material (base glass). As a result, isotopic compositions for one CRM cannot be extrapolated to another, and each must be calibrated for use independently. We present the first compilation of working values for these glasses.