Abstract:A study on Pb isotopes was conducted within the soil–plant–aerosol system. The results indicate that Pb isotopes serve as a suitable tool not only for tracing atmospheric pollution sources but also for tracking the Pb transfer process into and within plants. The main findings are as follows: 1) Pb isotopes in plants are a powerful tool for tracing Pb sources. When plants are removed from their original location, Pb isotopes in the whole plant or roots are suitable for tracing their growth sites; Pb isotopes in leaves are suitable for tracing aerosol particles in the surrounding environment; however, Pb isotopes in stems are not suitable for tracing Pb sources. 2) Pb isotopic fractionation occurs during the growth process of E. splendens Nakai (δ208Pb?????–???? = -4.31 to 0.30‰), and the extent of fractionation is larger than that of most mineral nutrients. This study also demonstrates that Pb isotopes in plants are a powerful tool for tracing the absorption and transport processes of Pb into and within the plant. Regardless of whether Pb is absorbed through the roots or leaves, lighter isotopes tend to be preferentially enriched in the subsequent tissues (from soil to root, from root to stem, and from leaf to stem within the plant), indicating non-selective absorption of Pb through ion channels. This is consistent with the diffusion effect on isotope ratio variation. Pb absorbed through the roots constitutes the main source of Pb in the plant. 3) The correlation between Pb isotope ratios could verify Pb pathways. Whether the correlation conforms to the principle of mass fractionation depends on whether Pb comes from one path or multiple pathways. This provides a new insight into understanding Pb sources in any physicochemical process or geological sample. 4) The addition of ethylene diamine disuccinic acid (EDDS, C??H??N?O?) promotes the uptake of Pb in the plant. However, it only affects the Pb concentration in the root and stem, but not in the leaf. This shows that altering soil state and promoting plant absorption are not ideal for reducing Pb pollution in soil for non-accumulator plants. The addition of EDDS in the soil also affects the variation in Pb isotope ratios within the plant. Compared with CK plants, heavier Pb isotopes were enriched in the EDDS-treated plants, which suggests a plant protection mechanism whereby heavier Pb isotopes are stored in biological macromolecules such as Pb-proteins/ligands to mitigate toxicity.

Abstract:Exploration for critical minerals, such as beryllium (Be) and uranium (U), requires accurate reserve assessment, for which drill core analysis is essential. Techniques like laser-induced breakdown spectroscopy (LIBS) and X-ray fluorescence spectroscopy (XRF) are widely used for rapid core analysis but have some limitations. LIBS suffers from poor sensitivity for low-concentration U, while XRF cannot detect Be. Furthermore, matrix effects in both techniques hinder the accurate simultaneous quantification of Be and U. We introduce a novel LIBS-XRF method for the simultaneous measurement of Be and low-concentration U. The methodology involves first analyzing samples with XRF and LIBS. Subsequently, a support vector machine (SVM) algorithm classifies the samples based on the XRF data. A separate predictive model is then developed for each category. A basic linear model is constructed using the spectral line of the target elements as the dominant factor based on dominant factor (DF) modeling strategy, and machine learning algorithms are then used to compensate for the residuals of this basic model. Tests on ore cores demonstrated that this method significantly reduces quantification errors. The achieved mean relative errors were 7.58% for Be and 7.02% for U. These results represent improvements of 61.42%/77.20% and 69.77%/72.48% over conventional unclassified and experience-based methods, respectively. This work is the first to use a LIBS-XRF approach for the highly accurate and simultaneous detection of Be and low-concentration U in ore cores, proving its high practical utility for this application.

Abstract:The search for carbonaceous matter in Martian rocks is the key to evaluating their potential biosignatures. Studying carbonaceous matter preserved within Earth’s basaltic analogs provides critical insights into the mineral–organic interactions that may also occur on Mars. To characterize molecular-level chemical information of carbonaceous matter, correlative surface-sensitive approaches such as Focused Ion Beam Scanning Electron Microscopy (FIB-SEM), Secondary Ion Mass Spectrometry (SIMS), and Atomic Force Microscopy Infrared Spectroscopy (AFM-IR) are employed. In this study, we developed a correlative microanalytical protocol starting with the ex-situ FIB-SEM lift-out, in which lamellae from a Mars-analog basalt were transferred onto a clean silicon substrate using a glass-needle nanomanipulator. The lamellae were then analyzed sequentially by Time-of-Flight SIMS (TOF-SIMS), AFM-IR, and Nano-scale Secondary Ion Mass Spectrometry (NanoSIMS). Specifically, spatially and chemically co-registered TOF-SIMS, AFM-IR, and NanoSIMS analyses provided complementary insights into the same region, correlating organic distribution, molecular vibrations, and isotopic compositions within mineral matrices. Together, these results demonstrate that the established correlative microanalytical protocol in this study effectively integrates sample preparation and multi-modal surface analyses, providing a framework for investigating planetary materials and future Mars samples.

Abstract:Elemental analyzer - isotope ratio mass spectrometry (EA-IRMS) is the most popular method for the measurement of sulfur isotopes in various samples including sulfide, sulfate and organosulfur compounds. The precision of ~±0.3‰ (1σ) can be achieved for samples with ~100 μg S. However, for samples with low sulfur content, or organic matter in particular (e.g., animal bone collagen), the precise and accurate sulfur isotope analysis remains challenging, with typical δ34S precision ranging from ±0.3‰ to ±1‰. In this study, we applied an improved EA-IRMS with a custom-built cryofocus device for the analysis of sulfur isotopes in organic matter. After sample combustion, all the product gases were transferred into a cold trap by a fast helium flow (100 mL/min). SO2 was then separated from other gases through a packed gas chromatographic (GC) column at lower flow rate (10 mL/min). The sample size of this method is ~300 nmol S, which is only 1/10 of that required by the conventional method. Lowered sample size allows fully oxygen isotope homogenization of sample SO2 with oxygen buffers during combustion. With this method, the δ34S precision from the measurement of organosulfur standards was better than ±0.3‰.

Abstract:Zircon U-Pb and Hf-O isotope compositions preserve valuable records of the formation and evolution of geological processes. To obtain accurate and precise zircon geochronology and Hf-O isotope ratios using in situ techniques, matrix-matched reference materials are essential. In this study, we introduce a new potential zircon reference material, the Perilla megacryst, which has homogeneous U-Pb ages and Hf-O isotopic compositions, as demonstrated by multiple analytical techniques. The chemical abrasion isotope dilution thermal ionization mass spectrometry (CA-ID-TIMS) method presents a weighted mean 206Pb/238U age of 42.40 ± 0.06 Ma (2σ, n = 8). Further examination of the heterogeneity of U-Pb ages of the Perilla zircon megacryst was conducted by secondary ion mass spectrometry (SIMS) and laser ablation (multiple collector) inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) among six laboratories. We obtained mean 206Pb/238U ages of 42.6 ± 0.3 Ma (2σ, n = 23) using SIMS (SHRIMP), 42.6 ± 0.3 Ma (2σ, n = 20) using SIMS (CAMECA), 42.2 ± 0.3 Ma (2σ, n = 14) using LA-MC-ICP-MS, and 42.6 ± 0.1 Ma (2σ, n = 207) using LA-Q-ICP-MS, respectively. The Hf isotopic compositions of Perilla were evaluated using LA-MC-ICP-MS, yielding a uniform mean 176Hf/177Hf ratio of 0.282565 ± 0.000040 (2SD, n = 149) among four laboratories. Oxygen isotope analysis using laser fluorination yielded results consistent with SIMS data, providing a recommended mean δ18O value of 6.53 ± 0.34 ‰ (2SD, n = 5). The reproducibility of results obtained from multiple analytical techniques across different laboratories demonstrate the homogeneity of U-Pb ages and Hf-O isotopic compositions in the Perilla zircon megacryst. Based on these results, we propose the Perilla zircon megacryst as a potential secondary reference material for external monitoring or analytical validation of Cenozoic U-Pb geochronology and Hf-O isotopic measurements.

Abstract:High precision magnesium isotope data have been widely used in geological and astrochemical research. Previous studies used cation-exchange resins (e.g., AG50W-X8, AG50W-X12, AGMP-50) for Mg purification of routine geological samples, and these Mg purification protocols yield solutions meeting multiple-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) analytical requirements, but one problem with the reported protocols is that the elution procedure is complex and time-consuming. In addition, some manganese nodule and shale samples have high Mn/Mg mass ratios. Previous studies have used highly concentrated HCl (e.g., 9–12 mol·L?1 HCl) or acetone (95%) to separate Mg from Mn and other elements. However, a low Mn removal efficiency, alongside the toxicity of acetone, may limit the purification of Mg in high-Mn samples (Mn/Mg >16), suggesting that further improvements should be made to the protocol. Here, we developed an efficient, user-friendly, and highly robust protocol for Mg isotope purification and analysis by MC-ICP-MS. Briefly, to isolate Mg from high-Mn matrices, an initial separation from matrix elements (e.g., Mn, Cu, Zn) was performed using AGMP-1M resin (100–200 mesh) eluted with 4.5 mL of 10 mol·L?1 HCl. A subsequent purification step using AG50W-X12 resin (200–400 mesh) was applied to remove major residual matrix elements with a mixed HNO?–HF solution, and Mg was finally collected by elution with 8 mL of 2 mol·L?1 HNO?. With this method, the yield during Mg purification was ~100%, and after one column or a two-column pass, most geological samples were suitable for high-precision Mg isotope analysis. We demonstrate that our method yields accurate Mg isotope ratios with a precision of ±0.07‰ for δ2?Mg, based on analyses of seawater, basalt, granodiorite, shale, manganese nodule, and carbonate reference materials.

Abstract:Stable isotope systems of iron, copper, and zinc have emerged as powerful tracers in understanding metal sources, migration, and deposit formation processes. Accurate and precise determination of Fe, Cu, and Zn isotopic compositions in sulfide minerals, especially in simple-matrix minerals characterized by their relatively pure composition, with low content of impurity elements and few interfering components, requires matrix-matched reference materials to validate analytical methods, particularly for direct analysis protocols without column chromatography. This study introduces a suite of novel secondary reference materials (NWU-Fe, NWU-Cu, and NWU-Zn sulfide powders) developed to address the critical gap in calibration standards for direct isotopic analysis without column chemistry of simple-matrix minerals. These sulfide powders exhibit excellent homogeneity and stability, fulfilling the requirements for high-precision determination of Fe, Cu, and Zn isotope ratios using MC-ICP-MS without column chemistry. Reference values were derived from interlaboratory comparisons across three independent laboratories. The isotopic compositions (δ-values), reported in per mil notation relative to international standards (IRMM-014 for Fe, NIST SRM-976 for Cu, and JMC-Lyon for Zn), are as follows: δ56Fe = -0.38 ± 0.03‰ (2s), δ65Cu = 0.44 ± 0.04‰ (2s), δ66Zn = -0.04 ± 0.02‰ (2s). This study provides a robust calibration framework for Fe-Cu-Zn isotopic studies in geochemistry and environmental science.