Pb Isotope Ratio Measurements Research Articles

Investigating Influences on the Pb Pseudo‐Isochron Using Three‐Dimensional Mantle Convection Models With a Continental Reservoir

AbstractFor mid‐ocean ridge basalts and ocean island basalts, measurements of Pb isotope ratios show broad linear correlations with a certain degree of scatter. In 207Pb/204Pb—206Pb/204Pb space, the best fit line defines a pseudo‐isochron age (τPb) of ∼1.9 Gyr. Previous modeling suggests a relative change in the behaviors of U and Pb between 2.25 and 2.5 Ga, resulting in net recycling of HIMU (high U/Pb) material in the latter part of Earth's history, to explain the observed τPb. However, simulations in which fractionation is controlled by a single set of partition coefficients throughout the model runs fail to reproduce τPb and the observed scatter in Pb isotope ratios. We build on these models with 3D mantle convection simulations including parameterizations for melting, U recycling from the continents and preferential removal of Pb from subducted oceanic crust. We find that both U recycling after the great oxygenation event and Pb extraction after the onset of plate tectonics, are required in order to fit the observed gradient and scatter of both the 207Pb/204Pb—206Pb/204Pb and 208Pb/204Pb—206Pb/204Pb arrays. Unlike much previous work, our model does not require accumulations of subducted oceanic crust to persist at the core‐mantle boundary for long periods of time in order to match geochemical observations.

Lead geochemistry of sediments in Galveston Bay, Texas

The geochemical behavior of Pb in terrestrial and coastal water systems significantly influences Pb biogeochemical cycling and pollutant exchange at the land-sea continuum. An ideal case study of Pb environmental geochemistry is Galveston Bay, an anthropogenic estuary exposed to industrial runoff, wastewater and shipping vessel spills but also fed by natural rivers. Here, sediments from Galveston Bay were measured for Pb isotope ratios and abundances to constrain Pb sources and fluxes and understand Pb pollution history in the bay. Lead isotopes have been established as source tracers of environmental pollution and allow Pb sources to be reliably fingerprinted and identified. Sediments were leached to distinguish authigenic sediment coatings from lithogenic residual sediments, in addition to bulk sediment digestions. Total Pb concentrations ranged from 1.76 µg/g–29.19 µg/g in bulk digests, which are below federal toxicity thresholds and aligns well with prior measurements of Pb in Galveston Bay sediments in the 20th century. Lead concentrations are spatially constrained by flocculation in eastern bay areas where the Trinity River enters the bay and positively temporally correlated to freshwater discharge. Sediment 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb ratios range between 18.338–19.777±0.002, 15.557–15.755±0.002 and 37.913–43.340±0.005, respectively, and were used in an advanced Bayesian isotope mixing model to identify Pb sources in the Galveston Bay sediment fractions analyzed. Anthropogenic sources supply approximately 83.8%, 16.6% and 25.5% of Pb to the leachates, residues and bulk sediments, respectively. This study showcases the importance of estuaries in moderating terrestrial and marine Pb distribution and provides insight for future contaminant studies in Galveston Bay and other estuarine systems around the world.MAIN FINDINGS Pb isotope ratio and abundance measurements of Galveston Bay sediments demonstrate significant anthropogenic Pb inputs to the estuary despite low Pb levels.

Direct determination of Pb isotope ratios in archaeological materials by coupling liquid chromatography to multicollector ICP-MS

On-line coupling of HPLC-MC-ICP-MS allows Pb isotope ratio measurements in archaeological samples without prior off-line Pb separation.

Assessment of Nanosecond Laser Ablation Multi‐Collector Inductively Coupled Plasma‐Mass Spectrometry for Pb and Sr Isotopic Determination in Archaeological Glass: Mass Bias Correction Strategies and Results for Corning Glass Reference Materials

This work presents an evaluation of various methods for in situ high‐precision Sr and Pb isotopic determination in archaeological glass (containing 100–500 μg g−1 target element) by nanosecond laser ablation multi‐collector‐inductively coupled plasma‐mass spectrometry (ns‐LA‐MC‐ICP‐MS). A set of four soda‐lime silicate glasses, Corning A–D, mimicking the composition of archaeological glass and produced by the Corning Museum of Glass (Corning, New York, USA), were investigated as candidates for matrix‐matched reference materials for use in the analysis of archaeological glass. Common geological reference materials with known isotopic compositions (USGS basalt glasses BHVO‐2G, GSE‐1G and NKT‐1G, soda‐lime silicate glass NIST SRM 610 and several archaeological glass samples with known Sr isotopic composition) were used to evaluate the ns‐LA‐MC‐ICP‐MS analytical procedures. When available, ns‐LA‐MC‐ICP‐MS results for the Corning glasses are reported. These were found to be in good agreement with results obtained via pneumatic nebulisation (pn) MC‐ICP‐MS after digestion of the glass matrix and target element isolation. The presence of potential spectral interference from doubly charged rare earth element (REE) ions affecting Sr isotopic determination was investigated by admixing Er and Yb aerosols by means of pneumatic nebulisation into the gas flow from the laser ablation system. It was shown that doubly charged REE ions affect the Sr isotope ratios, but that this could be circumvented by operating the instrument at higher mass resolution. Multiple strategies to correct for instrumental mass discrimination in ns‐LA‐MC‐ICP‐MS and the effects of relevant interferences were evaluated. Application of common glass reference materials with basaltic matrices for correction of ns‐LA‐MC‐ICP‐MS isotope data of archaeological glasses results in inaccurate Pb isotope ratios, rendering application of matrix‐matched reference materials indispensable. Correction for instrumental mass discrimination using the exponential law, with the application of Tl as an internal isotopic standard element introduced by pneumatic nebulisation and Corning D as bracketing isotopic calibrator, provided the most accurate results for Pb isotope ratio measurements in archaeological glass. Mass bias correction relying on the power law, combined with intra‐element internal correction, assuming a constant 88Sr/86Sr ratio, yielded the most accurate results for 87Sr/86Sr determination in archaeological glasses

Development of procedure for measurement of Pb isotope ratios in seawater by application of seaFAST sample pre-treatment system and Sector Field Inductively Coupled Plasma Mass Spectrometry

Anthropogenic Pb in the oceans, derived from high-temperature industrial processes, fuel combustion and incineration can have an isotopic signature distinct from naturally occurring Pb, supplied by rock weathering. To identify the different pollution sources accurately and to quantify their relative contributions, Pb isotope ratios are widely used.Due to the high salt content (approximately 3.5% of total dissolved solids) and very low levels of Pb (typically from 1 to 100ngL−1) in seawater the determination of Pb isotope ratios requires preliminary matrix separation and analyte preconcentration. An analytical protocol for the measurements of Pb isotope ratios in seawater combining seaFAST sample pre-treatment system and Sector Field Inductively Coupled Plasma Mass Spectrometry (SF ICP-MS) was developed. The application of seaFAST system was advantageous, because of its completely closed working cycle and small volumes of chemicals introduced in pre-treatment step, resulting in very low detection limits and procedural blanks.The preconcentration/matrix separation step was also of crucial importance for minimizing the isobaric and matrix interferences, coming from the seawater. In order to differentiate between anthropogenic and natural Pb sources, particular attention was paid to the determination of 204Pb isotope because of its implication in some geological interpretations.The validation of the analytical procedure was effectuated according to the recommendations of the ISO/IEC 17025 standard. The method was validated by processing the common Pb isotope reference material NIST SRM 981. All major sources of uncertainty were identified and propagated together following the ISO/GUM guidelines. The estimation of the total uncertainty associated to each measurement result was fundamental tool for sorting the main sources of possible biases. The developed analytical procedure was applied to the coastal and open seawater samples, collected in different regions of the world and revealed that the procedure is applicable for the measurement of Pb isotope ratios in seawater with combined uncertainty adequate to discuss the origin of Pb pollution in the ocean.

Identification of sources of lead in the atmosphere by chemical speciation using X-ray absorption near-edge structure (XANES) spectroscopy

Sources of Pb pollution in the local atmosphere together with Pb species, major ions, and heavy metal concentrations in a size-fractionated aerosol sample from Higashi-Hiroshima (Japan) have been determined by X-ray absorption near-edge structure (XANES) spectroscopy, ion chromatography, and ICP-MS/AES, respectively. About 80% of total Pb was concentrated in fine aerosol particles. Lead species in the coarse aerosol particles were PbC2O4, 2PbCO3·Pb(OH)2, and Pb(NO3)2, whereas Pb species in the fine aerosol particles were PbC2O4, PbSO4, and Pb(NO3)2. Chemical speciation and abundance data suggested that the source of Pb in the fine aerosol particles was different from that of the coarse ones. The dominant sources of Pb in the fine aerosol particles were judged to be fly ash from a municipal solid waste incinerator and heavy oil combustion. For the coarse aerosol particles, road dust was considered to be the main Pb source. In addition to Pb species, elemental concentrations in the aerosols were also determined. The results suggested that Pb species in size-fractionated aerosols can be used to identify the origin of aerosol particles in the atmosphere as an alternative to Pb isotope ratio measurement.

Final report of the key comparison CCQM-K98: Pb isotope amount ratios in bronze

Isotope amount ratios are proving useful in an ever increasing array of applications that range from studies unravelling transport processes, to pinpointing the provenance of specific samples as well as trace element quantification by using isotope dilution mass spectrometry (IDMS). These expanding applications encompass fields as diverse as archaeology, food chemistry, forensic science, geochemistry, medicine and metrology. However, to be effective tools, the isotope ratio data must be reliable and traceable to enable the comparability of measurement results.The importance of traceability and comparability in isotope ratio analysis has already been recognized by the Inorganic Analysis Working Group (IAWG) within the CCQM. While the requirements for isotope ratio accuracy and precision in the case of IDMS are generally quite modest, 'absolute' Pb isotope ratio measurements for geochemical applications as well as forensic provenance studies require Pb isotope ratio measurements of the highest quality. To support present and future CMCs on isotope ratio determinations, a key comparison was urgently needed and therefore initiated at the IAWG meeting in Paris in April 2011. The analytical task within such a comparison was decided to be the measurement of Pb isotope amount ratios in water and bronze.Measuring Pb isotope amount ratios in an aqueous Pb solution tested the ability of analysts to correct for any instrumental effects on the measured ratios, while the measurement of Pb isotope amount ratios in a metal matrix sample provided a real world test of the whole chemical and instrumental procedure. A suitable bronze material with a Pb mass fraction between 10 and 100 mg•kg-1 and a high purity solution of Pb with a mass fraction of approximately 100 mg•kg-1 was available at the pilot laboratory (BAM), both offering a natural-like Pb isotopic composition.The mandatory measurands, the isotope amount ratios n(206Pb)/n(204Pb), n(207Pb)/n(204Pb) and n(208Pb)/n(204Pb) were selected such that they correspond with those commonly reported in Pb isotopic studies and fully describe the isotopic composition of Pb in the sample. Additionally, the isotope amount ratio n(208Pb)/n(206Pb) was added, as this isotope ratio is typically measured when performing Pb quantitation by IDMS involving a 206Pb spike.Each participant was free to use any method they deemed suitable for measuring the individual isotope ratios. However, the majority of the results were obtained by using muIti-collector ICPMS or TIMS. The key requirements for all analytical procedures were a traceability statement for all results and the establishment of an uncertainty budget meeting a target uncertainty for all ratios of 0.2 %, relative (k=1). Additionally, the use of a Pb-matrix separation procedure was encouraged.The obtained overall result was excellent, demonstrating that the individual results reported by the NMIs/DIs were comparable and compatible for the determination of Pb isotope ratios. MC-ICPMS and MC-TIMS data were consistent with each other and agree to within 0.05 %. The corresponding uncertainties can be considered as realistic uncertainties and mainly range from 0.02 % to 0.08 % (k=1).As stated above isotope ratios are being increasingly used in different fields. Despite the availability and ease of use of new mass spectrometers, the metrology of unbiased isotope ratio measurements remains very challenging. Therefore, further comparisons are urgently needed, and should be designed to also engage scientists outside the NMI/DI community. Possible follow-up studies should focus on isotope ratio and delta measurements important for environmental and technical applications (e.g. B), food traceability and forensics (e.g. H, C, N, O, S and 87Sr/86Sr) or climate change issues (e.g. Li, B, Mg, Ca, Si).Main text.To reach the main text of this paper, click on Final Report.The final report has been peer-reviewed and approved for publication by the CCQM.

Lead isotope ratios in till and vegetation over a VMS occurrence under significant allochthonous cover

Two size fractions of till, <250 μm and <2 μm, humus, moss and black spruce bark, as well as sulphides, host rocks and Palaeozoic cover dolostone from drill cores were sampled at the Talbot Lake volcanogenic massive sulphide (VMS) prospect in the Flin Flon-Snow Lake terrane, Manitoba, Canada. Lead isotope-ratios in organic surface media indicate significant input of anthropogenic Pb from the Flin Flon smelter at 160 km distance to the northwest, with 206 Pb/ 204 Pb between 16.5 and 18.2, whereas background till and upper dolostone range between 21.6 and 23.1. At deeper levels, the influx of Pb from Proterozoic mineralization from greater than 100 m depth is recognized. Strontium isotope ratios in these media indicate enhanced vertical fluid flow in the till cover at a fault zone, coincident with the Pb isotope anomaly, as well as relative contributions of Sr from carbonates, silicates and vegetation to the till profile. In humus, sphagnum moss and black spruce bark, the Pb isotope ratios are progressively more similar to that of the feed of the Flin Flon smelter. Measurements of Pb and Sr isotope ratios reveal that Pb from Proterozoic mineralization situated beneath 100 m of Palaeozoic dolostone can be distinguished from Pb contributed by anthropogenic and other geogenic sources.

The measurement of Pb isotope ratios in sub-ng quantities by fast scanning single collector sector field-ICP-MS

This work describes an analytical protocol for the measurement of isotope ratios in samples containing small amounts of lead (i.e. ≤0.2ng total Pb) using the Nu Attom single collector-ICP-MS. The method was evaluated using the NIST SRM 981 isotopic standard and standard-sample bracketing for correction of the instrumental mass fractionation. The long-term precision (n=32, ±2SD) was 0.11% for the 208Pb/206Pb and 207Pb/206Pb ratios and 0.21–0.23% for the 20xPb/204Pb ratios (where x=208, 207, 206). The precision of the measured Pb isotope ratios reported here (for equivalent total Pb quantities) is comparable to multi-collector (MC) methodologies, using either an array of ion counters (Cocherie and Robert, 2007, Chem. Geol. 243, 90–104) or conventional Faraday collectors coupled with a high efficiency sample cone (Makishima and Nakamura, 2010, J. Anal. At. Spectrom. 25, 1712–1716). The accuracy of the measured Pb isotope ratios and the effect of the sample matrix were evaluated for a series of USGS rock standard digests and doped solutions of the NIST SRM 981 standard. For total cation concentrations <10μgmL−1 and concomitant low concentrations (<1.5μgmL−1) of easily ionisable elements (i.e. Na and K), matrix effects were not resolvable at the level of precision reported. However, significant matrix effects were associated with sample compositions typical of natural waters, and removal of (at least) the major cations is required for accurate isotope ratio measurements.

Rapid Release and Changing Sources of Pb in a Mountainous Watershed during Extreme Rainfall Events

Although atmospheric Pb is known to accumulate in forest soils over time, little is known about the hydrologic Pb export from mountain forest soils. Short-term changes in Pb release and its sources during monsoon rainfall events were investigated in a mountainous watershed in the northern extreme of South Korea by combining intensive storm sampling with measurements of Pb concentrations and isotope ratios in soils and size-fractionated sediments. Biweekly monitoring of forest and agricultural streams showed relatively low dissolved Pb concentrations compared to those found in precipitation. Particulate Pb concentrations in both streams were higher than the dissolved concentrations and increased rapidly during rainfall events. Particulate Pb concentrations were substantially higher in the agricultural stream; the highest concentrations were associated with silt-size sediment followed by sand. A comparison of (206)Pb/(207)Pb and (208)Pb/(206)Pb among sediment fractions and source soils indicated that major sources for silt- and sand-associated Pb in the agricultural stream change between streambank and cropland soils, whereas Pb in the forest stream is primarily derived from forest floors. The results suggest that Pb isotopes can be efficiently applied to tracing short-term changes in sediment and Pb sources and that extreme rainfall events can significantly increase Pb mobilization from erosion-prone mountain soils.

Evaluation of zinc, cadmium and lead isotope fractionation during smelting and refining

To evaluate metallurgical processing as a source of Zn and Cd isotopic fractionation and to potentially trace their distribution in the environment, high-precision MC-ICP-MS Zn, Cd and Pb isotope ratio measurements were made for samples from the integrated Zn–Pb smelting and refining complex in Trail, B.C., Canada. Significant fractionation of Zn and Cd isotopes during processing of ZnS and PbS ore concentrates is demonstrated by the total variation in δ 66/64Zn and δ 114/110Cd values of 0.42‰ and 1.04‰, respectively, among all smelter samples. No significant difference is observed between the isotopic compositions of the Zn ore concentrates ( δ 66/64Zn = 0.09 to 0.17‰; δ 114/110Cd = − 0.13 to 0.18‰) and the roasting product, calcine ( δ 66/64Zn = 0.17‰; δ 114/110Cd = 0.05‰), due to ∼ 100% recovery from roasting. The overall Zn recovery from metallurgical processing is ∼ 98%, thus the refined Zn metal ( δ 66/64Zn = 0.22‰) is not significantly fractionated relative to the starting materials despite significantly fractionated fume ( δ 66/64Zn = 0.43‰) and effluent ( δ 66/64Zn = 0.41 to 0.51‰). Calculated Cd recovery from metallurgical processing is 72–92%, with the majority of the unrecovered Cd lost during Pb operations ( δ 114/110Cd = − 0.38‰). The refined Cd metal is heavy ( δ 114/110Cd = 0.39 to 0.52‰) relative to the starting materials. In addition, significant fractionation of Cd isotopes is evidenced by the relatively light and heavy isotopic compositions of the fume ( δ 114/110Cd = − 0.52‰) and effluent ( δ 114/110Cd = 0.31 to 0.46‰). In contrast to Zn and Cd, Pb isotopes are homogenized by mixing during processing. The total variation observed in the Pb isotopic compositions of smelter samples is attributed to mixing of ore sources with different radiogenic signatures.

Lead concentrations and isotopes in corals and water near Bermuda, 1780–2000

The history of the oceanic anthropogenic lead (Pb) transient in the North Atlantic Ocean for the past 220 yr is documented here from measurements of Pb concentration and isotope ratios from annually-banded corals that grew in coastal seawaters near Bermuda and from seawater samples collected during the last 20 yr of the 20th century. Anthropogenic Pb emissions in this area have been dominated by the industrialization of North America beginning in the 1840s, the introduction of leaded gasoline beginning in the 1920s and its phase-out that began in the mid-1970s. The phase-out of leaded gasoline was largely completed by the late 1990s. Coral Pb concentrations occur at a constant low level of about 5 nmol Pb/mol Ca (~ 15 pmol/kg in seawater) from the late 1700s to ~ 1850. From ~ 1850 to ~ 1900 there is a small increase rising to a plateau at ~ 25 nmol Pb/mol Ca (~ 80 pmol/kg in seawater) in the 1930s until the late 1940s, at which point Pb concentrations rapidly increase to ~ 60 nmol Pb/mol Ca (~ 200 pmol/kg in seawater). In the mid 1970s, Pb began to decline to ~ 25 nmol Pb/Ca (40 pmol/kg in seawater) by the end of the 20th century, comparable to levels occurring in the early 20th century. Pb isotope ratios (Pb I.R.) show maximum 206Pb/ 207Pb = 1.21 and 208Pb/ 207Pb = 2.49 in the middle of the 19th century. We conclude that this signal is a reflection of the early dominance of Upper Mississippi Valley Pb ore in the United States, as previously seen in the estuarine sediments of Rhode Island. After 1900, Pb I.R. decrease only slightly until the 1960s when there is a significant local maximum in the 1970s to 206Pb/ 207Pb = 1.19 and 208Pb/ 207Pb = 2.45 as low-Pb I.R. sources were phased out in the United States. Then, as US leaded gasoline utilization decreased more rapidly than European Pb gas utilization (which has lower Pb I.R.), western North Atlantic Pb I.R. decreased to 206Pb/ 207Pb = 1.17 and 208Pb/ 207Pb = 2.44, their lowest values in the past two centuries.

An ultra-clean technique for accurately analysing Pb isotopes and heavy metals at high spatial resolution in ice cores with sub-pg g −1 Pb concentrations

Measurements of Pb isotope ratios in ice containing sub-pg g −1 concentrations are easily compromised by contamination, particularly where limited sample is available. Improved techniques are essential if Antarctic ice cores are to be analysed with sufficient spatial resolution to reveal seasonal variations due to climate. This was achieved here by using stainless steel chisels and saws and strict protocols in an ultra-clean cold room to decontaminate and section ice cores. Artificial ice cores, prepared from high purity water were used to develop and refine the procedures and quantify blanks. Ba and In, two other important elements present at pg g −1 and fg g −1 concentrations in Polar ice, were also measured. The final blank amounted to 0.2 ± 0.2 pg of Pb with 206Pb/ 207Pb and 208Pb/ 207Pb ratios of 1.16 ± 0.12 and 2.35 ± 0.16, respectively, 1.5 ± 0.4 pg of Ba and 0.6 ± 2.0 fg of In, most of which probably originates from abrasion of the steel saws by the ice. The procedure was demonstrated on a Holocene Antarctic ice core section and was shown to contribute blanks of only ∼5%, ∼14% and ∼0.8% to monthly resolved samples with respective Pb, Ba and In concentrations of 0.12 pg g −1, 0.3 pg g −1 and 2.3 fg g −1. Uncertainties in the Pb isotopic ratio measurements were degraded by only ∼0.2%.

In-situ analysis of Pb isotope ratios using laser ablation MC-ICP-MS: Controls on precision and accuracy and comparison between Faraday cup and ion counting systems

This contribution compares in-situlaser ablation multicollector ICP-MS (LA-MC-ICP-MS) measurements of Pb isotope composition using parallel Faraday cup and ion counter detector array to those made using solely Faraday cups. In the former configuration ion counting is used for the low abundance isotope 204Pb as well as 200Hg and 202Hg isotopes required for correction of isobaric interference of 204Hg. Accurate measurement of the differences in gain between ion counters and Faraday cups, required for determination of 208Pb/204Pb, 207Pb/204Pb and 206Pb/204Pb ratios using ion counting, can be made by analysis of standard glasses to within ±0.3% (2s). For analyses made using Faraday cups or combined Faraday cup and ion counting detector arrays mass bias is effectively controlled by external normalization to 208Pb/206Pb ratios measured in the same standard glasses. Provided that He sweep gas flow rates are kept constant and that adequate time is allowed for stabilization after changes in He flow, mass bias can be controlled to within ±0.05% (2s). The precision of measurements of Pb isotope ratios is strongly dependent on ion beam intensities. Internal precision of ≤ 0.02% (2se) on 208Pb/206Pb and 207Pb/206Pb ratios requires ∑Pb ion beam intensity of > ∼30–50 mV. At beam intensities ∼200 mV, equivalent to ∼100 000 counts per second (cps) 204Pb. Correction for 204Hg interference does not substantially contribute to uncertainty as long as 204Hg comprises less than ∼20% of the total 204 ion beam.

New sequential separation procedure for Sr, Nd and Pb isotope ratio measurement in geological material using MC-ICP-MS and TIMS

A new 3-step sequential separation chemistry for Sr, Nd and Pb from silicate samples, which is suitable for isotope analysis by MC-ICP-MS as well as TIMS, has been developed. The chemistry is designed to minimize the number of evaporation steps, enabling high throughput especially when MC-ICP-MS is employed. The sample solution in 0.5 mol l-1 HNO3 after digestion with HF-HClO4, which is prepared for trace element analysis, can be directly used in the new chemistry. In the first column using Sr resin, Sr and Pb are collected. The recovered solution for Sr can be directly aspirated into MC-ICP-MS. The Pb solution is dried, re-dissolved, separated into two aliquots and measured by double spike MC-ICP-MS. Subsequently, LREEs are collected by the second column packed with cation exchange resin. Finally, Nd was purified from Sm using Ln resin in the third column. The recovered Nd solution can also be directly nebulized into MC-ICP-MS. The Sr and Nd isotope ratios for the standard material JB-3 (basalt) from the Geological Survey of Japan by MC-ICP-MS and TIMS were reported to verify the chemistry and mass spectrometry developed in this study.

Influence of non-spectral matrix effects on the accuracy of Pb isotope ratio measurement by MC-ICP-MS: implications for the external normalization method of instrumental mass bias correction

Ca, Al, Fe and Mg are identified as the dominant inorganic matrix components in Pb purified by anion exchange chromatography from a wide compositional range of silicate samples. Doping experiments demonstrate that these elements cause non-spectral matrix effects that result in inaccuracy of mass bias-corrected MC-ICP-MS Pb isotope ratios ranging from −150 to +120 ppm per amu. Although small, these inaccuracies are significant at the level of precision required for application in mantle geochemistry today. The inaccuracy results from matrix induced per mil level variation in the Tl to Pb mass bias ratio (δf(Tl)/f(Pb)‰). In matrix-free standards, δf(Tl)/f(Pb)‰ varies from −0.30 to +0.21‰, depending on run conditions, whereas the mean δf(Tl)/f(Pb) in matrix experiments varies from −1.45‰ with an Fe matrix to 7.11‰ with a Ca matrix. The matrix also causes increased Pb and Tl sensitivity. Signal enhancement plateaus out at high matrix levels. This finite response to the matrix can be used as an advantage. With a common matrix of Mg added to both doped Pb(Tl) standards and their bracketing un-doped standards, variation in f(Tl)/f(Pb) is greatly reduced, resulting in external reproducibility of combined doped and un-doped Pb isotope ratios (30–61 ppm per amu) similar to single session external reproducibility of pure standards (20–60 ppm per amu). Addition of a common matrix to samples and standards may provide a viable alternative to thorough purification in the effort to reduce or eliminate non-spectral matrix effects in MC-IPC-MS isotope ratio measurements.

Polynomial mass bias functions for the internal standardization of isotope ratio measurements by multi-collector inductively coupled plasma mass spectrometry

The development and application of a calibration strategy for routine isotope ratio analysis by multi-collector inductively coupled plasma mass spectrometry (ICP-MS) is described and assessed. Internal standardization was used to account for the mass dependant determinate error (mass bias). The general solution for polynomial isotope ratio mass bias functions for use with internal standardization and isotope ratio measurements by multi-collector inductively coupled plasma mass spectrometry was derived. The resulting linear isotope ratio mass bias function was demonstrated to be mathematically consistent and experimentally realistic for the analysis of acidified aqueous solutions of analyte and internal standard elements (clean solutions) by multi-collector inductively coupled plasma mass spectrometry. The calibration strategy was applied to the measurement of Pb, Sm and Ni isotope ratios in clean solutions using Tl, Eu and Cu as internal standards, respectively. Results of the analysis of the standard reference material NBS 982 for 208Pb/ 206Pb, 207Pb/ 206Pb and 204Pb/ 206Pb isotope ratios were 1.000290 ± 0.000025, 0.466994 ± 0.000008 and 0.027218 ± 0.000003 (± 1 standard deviation, n = 48) with errors of (+ 0.0130 ± 0.0025)%, (− 0.0271 ± 0.0017)% and (− 0.005 ± 0.009)%, respectively.

Measurement of Pb isotope ratios by continuous leach–inductively coupled plasma–mass spectrometry: quantification of precision and accuracy

Precision and accuracy have been quantified for the determination of lead isotope ratios using continuous leach–inductively coupled plasma–mass spectrometry (CL-ICP-MS) by optimizing acquisition parameters and minimizing the number of elements in the method. By analysing for only 204 Pb, 206 Pb, 207 Pb, 208 Pb, 200 Hg, and 202 Hg, counting times can be increased allowing improvements in isotope ratio precision over normal CL-ICP-MS determinations, which measure these elements as part of a much larger suite. At total Pb concentrations of 1 ppb in solution, results show that precisions of 6.7% to 8.3% and 7.8% to 21% can be achieved for 207 Pb/ 206 Pb and 207 Pb/ 204 Pb, respectively, over the 0% to 30% HNO 3 concentrations used in CL-ICP-MS. Accuracy, as measured against the certified values for NIST 981, ranges from 0.5% to 1.4% and 1.4% to 21% for 207 Pb/ 206 Pb and 207 Pb/ 204 Pb, respectively. The improvement in precision and accuracy afforded by this technique allows greater differentiation of isotopically distinct reservoirs of Pb within natural samples collected for exploration and environmental geochemistry.

Identification of Pb sources in Yellow Sea sediments using stable Pb isotope ratios

Rapid economic developments in East Asian countries have inevitably resulted in environmental degradation in the surrounding seas, and concern for both the environment and protection from pollutants is increasing. Identification of sources of contaminants is essential to environmental pollution management. In this study, the provenance of anthropogenic lead (Pb), a major pollutant of Yellow Sea sediments, was determined for river mouth sediments, including those of the Changjiang, Huanghe, Han, and Geum Rivers, and for age-determined shelf core sediments through the measurement of Pb isotope ratios in the HCl-leached fraction using multi-collector inductively coupled plasma-mass spectrometry (MC ICP/MS). Anthropogenic Pb has accumulated in shelf core sediments since 1910, and its isotope ratios were estimated as 0.863–0.866 and 2.119–2.125 for 207Pb/ 206Pb and 208Pb/ 206Pb, respectively, from the mixing relationships of the two endmembers. River mouth sediments exhibited enough distinction in anthropogenic Pb isotope ratios to be discriminated: 0.874 (2.144) in the Huanghe, 0.856 (2.129) in the Han, 0.857 (2.122) in the Geum, and 0.854 (2.101) in the Changjiang for 207Pb/ 206Pb ( 208Pb/ 206Pb), respectively. Although isotope ratios of geogenic Pb in sediments dating before 1910 showed narrow ranges (0.842–0.845 and 2.088–2.100 for 207Pb/ 206Pb and 208Pb/ 206Pb, respectively), distinct isotope ratios in each core permitted source identification of sediments in the Yellow Sea based on geographic locations and the geogenic Pb of each river. By comparing the isotope ratios of the estimated anthropogenic Pb to source-related materials, the provenances of anthropogenic Pb in Chinese river sediments were presumed to be Chinese coal or ore, which is also a major source of atmospheric particulate Pb. The anthropogenic Pb in the shelf core sediments in the northern Yellow Sea originated from northern Chinese cities such as Beijing and Tianjin through atmospheric pathways. Pb isotope ratios indicated that Pb in Korean river sediments was characteristic of local Korean ores.

MPI‐DING glasses: New geological reference materials for in situ Pb isotope analysis

Advances in microanalytical techniques continue to revolutionize trace element and isotope geochemistry. Yet the lack of widely available geological reference materials has made interlaboratory comparisons and assessment of analytical accuracy difficult or impossible in many cases. The preparation and extensive analysis of the MPI‐DING glasses has been designed to fill this gap. Here we report high‐precision Pb isotope analyses by TIMS and MC‐ICPMS techniques on seven geological MPI‐DING glasses. The Pb concentrations in the reference glasses vary between 0.4 and 20 μg/g, allowing use in a wide range of analytical situations. In addition, solution ICPMS and LA‐ICPMS analyses were used to investigate the analytical performance of a rapidly scanning single‐collector sector‐field mass spectrometer for the measurement of Pb isotope ratios. Our TIMS and MC‐ICPMS measurements demonstrate that variations of 208Pb/206Pb and 207Pb/206Pb in most MPI‐DING glasses are less than 0.03%. Preliminary reference values for 208Pb/204Pb, 207Pb/204Pb, 206Pb/204Pb, 208Pb/206Pb, and 207Pb/206Pb were obtained by averaging all high‐precision data and normalizing them to the mean triple spike data for NIST SRM 981, obtained in the Mainz laboratory. 208Pb/206Pb and 207Pb/206Pb ratios, which are commonly utilized for in situ Pb isotope studies, vary from 2.0110 (GOR132‐G) to 2.0810 (T1‐G) and 0.81656 (GOR132‐G) to 0.84389 (GOR128‐G), respectively. Any heterogeneity present in the glasses is generally lower than the reproducibility obtained from in situ microanalytical techniques, such as LA‐ICPMS and SIMS (about 0.1–0.3% for 208Pb/206Pb and 207Pb/206Pb measurements). This is demonstrated by the results for our LA‐ICPMS Pb isotope analyses using a single‐collector sector‐field ICP mass spectrometer, which agree to within 0.2% of the reference values. A similar accuracy was obtained from solution ICPMS using the same single‐collector mass spectrometer.