Abstract:Particle size distribution (PSD) is a key feature of mineral fractions in soils and sediments. It directly affects many physical and mechanical properties that are closely related to the geological origin and evolution of soils and sediments. However, precise PSD measurement is still unrealized, especially for fine and precious samples such as lunar soils which require a noninvasive and nondestructive methodology. In this study, using Laser Diffraction Particle Size (LDPS) analysis as a reference, we compared PSD results of lunar soil simulants measured using three-dimensional X-ray Microscopy (XRM), Optical Microscopy (OM), and Scanning Electron Microscopy (SEM) approaches. Our experimental results showed that the PSD (in numbers) measured by the different methods was not consistent, whereas the PSD (in volume/area) showed some consistency, at least within a certain size range. Comparatively, (i) SEM reliably measured particles in the range of ~0.1-10 μm, (ii) OM was effective for particles with sizes ranging from ~10 to 75 μm, and (iii) XRM effectively measured those particles with sizes ranging from a few microns to a few hundred microns and showed relatively positive consistency with the LDPS result especially for particles above ~75 μm. By employing the Boltzmann model to integrate the particle size accumulation (PSA) data from different measurement methods, we propose a multi-approach method for the precise determination of particle size. This method can be applied for the particle size analysis of soils or regoliths returned from the Moon or other extraterrestrial objects.

Abstract:Spectroscopic interferences have long negatively impacted the accuracy of inductively coupled plasma mass spectrometry (ICPMS) analyses. Of these, oxide-based interferences, the combination of an analyte with oxygen producing a new ion 16 mass units greater than the original analyte, often proves most prevalent and difficult. A cheap and reliable method that permits the mitigation of oxide-based interference would be highly beneficial. Here-in, low sample uptake rate was used to reduce the formation of lanthanide oxide-based interferences in ICPMS analyses through temperature and Le Chatelier effects. Introduction of oxide forming solutions (50 μg L-1) composed of lanthanide elements at 1 mL/min yielded an average oxide ratio of 4.5 ± 7.2% while introduction at 50 μL L min-1 yielded 0.54 ± 0.26%. A similar method using 2% nitrogen gas in the bulk plasma concurrently decreased oxide-based interferences. The benefits observed with low sample uptake rate and a mixed-gas plasma were combined to virtually eliminate oxide based-interferences for many of the lanthanide elements and provide a modest signal enhancement compared to an Ar plasma operated at a higher sample uptake rate. For example, when comparing the best oxide reduction method to the worst, oxide formation is mitigated by 97%. Of the three sample uptake rates tested, 235 μL min-1 under mixed-gas plasma conditions offers the best balance between the oxide interferences mitigation and signal intensity. Ultimately, low sample uptake rate may prove essential in increasing ICPMS analysis accuracy while safeguarding resources and minimizing chemical waste for generations to come.

Abstract:In situ elemental analysis of carbonate matrices at the microscale is a rapidly developing and promising area of research with significant implications for fields including geology, environmental science, and biology. However, applications in these fields have been hampered by the lack of appropriate analytical reference materials and the ongoing need for improvements in analytical methods. This study used pure ooid sands from the modern Schooner Cays in the Bahamas as raw material due to their nearly consistent mineralogical compositions and uniform elemental distributions. A wet milling process was employed, and the Tyndall effect was used to isolate ultra-fine colloidal particles (most <1 μm). These particles underwent high-pressure compression, and the resulting pellets, namely OOID, were subsequently embedded in epoxy resin to ensure their long-term preservation and utility. Over a four-year study period, we confirmed that at least 28 elements remained homogeneously distributed within the reference material OOID. These results were achieved through rigorous relative standard deviation and Horwitz tests. The findings of this study underscored the crucial role of natural reference materials in ensuring quality control of in situ carbonate elemental analyses. Simultaneously, the study provided valuable new guidelines for preparing carbonate reference materials and improved the accuracy of in situ microanalytical methods for carbonate samples.

Abstract:This study presents a method for the reliable determination of 87Sr/86Sr in food grains, which are characterized by low Sr concentrations but high concentration ratios of Rb/Sr and K/Sr using multi‐collector inductively coupled plasma mass spectrometry (MC-ICP-MS). The Sr/matrix separation procedure using Sr resin was optimized for a standard reference material of wheat flour (NIST SRM 1567b). Consequently, a high Sr recovery (97.0 % ± 1.2 %, mean ± 1 SD, n = 7) and effective Sr/matrix separation (e.g., 85Rb/88Sr intensity ratio at MC-ICP-MS measurements × 100 of 0.00014 % ± 0.00003 %, mean ± 1 SD, n = 7) were achieved. Furthermore, potential spectroscopic interferences caused by matrix ions were estimated by analyzing NIST SRM 987 solutions spiked with varying amounts of Rb or Ca using MC-ICP-MS. The proposed method was validated by analyzing eight standard reference materials of vegetal, animal, and geological origins studied previously, yielding 87Sr/86Sr ratios consistent with literature values, which demonstrates the applicability of the method across diverse sample matrices. Finally, the proposed method was applied to standard reference materials for which 87Sr/86Sr ratios are not reported to our knowledge (NIST SRM 1567a and b wheat flour). The 87Sr/86Sr ratios of NIST SRM 1567a and b were estimated to be 0.70895 ± 0.00005 (2 SD, n = 34), and 0.70898 ± 0.00003 (2 SD, n = 25), respectively.

Abstract:The pivotal role of vegetation uptake in the global biogeochemical cycle of mercury (Hg) necessitates investigation on Hg species and transformation within plants, which have been limited by methodological constraints. This study established a temperature-programmed thermal desorption method to provide well-resolved thermal release profiles of Hg complexes with various biomolecules and Hg in plant tissues, showing significant differences from those of inorganic Hg compounds. Wild plant tissues and Hg(0)-exposed poplar leaves in the laboratory demonstrated consistency with Hg complexes with biomolecules at 180℃, 220℃, and 280℃. Besides, thermal release profiles revealed that a proportion of plant Hg is more thermally stable compared to Hg-biomolecule complexes. Specifically, for wild plants, 13%-42% of Hg in leaves was released above 300℃, and 61%-76% of Hg in roots was released between 280℃ and 450℃, likely caused by different matrices, Hg sources, and transformation processes. Results also revealed a complete transformation of Hg(0) into oxidized Hg after foliar Hg(0) uptake. The notable Hg release from 180℃ to 450℃ raises concerns about Hg emissions during various biomass thermal processes, beyond biomass burning. Therefore, controlling Hg release in these processes is promising for reducing emissions and producing low-Hg biofuels.

Abstract:Advancements in Zn isotope analytical methods and their widespread application in geosciences underscore the importance of the purification process in isotopic measurements. Efficient purification of Zn, which involves separating Zn from matrix elements, is essential for accurately determining Zn isotopic compositions. This study proposes an optimized purification method that combines precipitation and a chromatographic procedure, significantly enhancing the purification efficiency. Using the established purification process, nine widely available geological-certified reference materials with known Zn isotopic compositions yield δ66Zn values that are in agreement with most previously published data within two standard deviations (2s) of repeat measurements. In addition, the effects of the presence of matrix elements have been evaluated using Neptune Plus MC-ICP-MS in a wet plasma mode. The average δ66Zn value of the multi-elemental Zn standard GSB-1, prepared by adopting GSB with different matrix elements, demonstrates good consistency with the long-term measured value of the pure GSB-Zn solution after precipitation and chromatographic separation. This enhanced purification protocol for Zn isotope measurement applies to a diverse range of geological samples and reduces the time and chemical reagents required for purification compared to conventional methods.

Abstract:Bacteremia is an extremely serious infectious disease with high mortality rate and increasing incidence. Early diagnosis and prompt treatment is key to improve the cure rate. In this study, we developed an automated sample pretreatment device based on microfluidic chip and online coupled it with ICP-MS for the simultaneous identification of E. Coli O157:H7 and Salmonella in human blood. This method realized automated sample loading, pathogen capture, elemental labeling, and signal desorption on the microfluidic chip through an automated liquid transfer system and E. Coli O157:H7 and Salmonella were detected simultaneously online by ICP-MS. The linear ranges of 400-80,000 CFU mL-1 for E. coli O157:H7 and Salmonella, as well as a method detection limits of 200 CFU mL-1 for E. Coli O157:H7 and 152 CFU mL-1 for Salmonella were obtained under optimum experimental conditions. The proposed approach realized the automated sample pretreatment and the simultaneous identification of two different kinds of bacteria in human whole blood, avoiding cumbersome sample pretreatment operations and sample contamination in conventional ICP-MS based procedures with elemental labeling strategy for bacteria analysis, demonstrating a strong potential for the clinical applications of bacteremia diagnosis.

Abstract:The increasing global popularity of traditional Chinese medicines (TCMs) raises significant concerns about potential contamination with organophosphorus pesticides (OPs). Portable analytical methods are particularly valuable for on-site pesticide analysis, enabling rapid screening and enhancing the safety assurance of TCM products. This study investigates the use of miniaturized microplasma atomic emission spectrometry (AES) as a promising tool for methyl parathion (MP) analysis in TCMs, leveraging the inhibition effect of OPs on butyrylcholinesterase (BChE) within a gold filament enrichment coupling point discharge chemical vapor generation atomic emission spectrometry (PD-CVG-AES) system. Specifically, BChE catalyzes the hydrolysis of acetylthiocholine chloride (ATCh) to form thiocholine (TCh), which contains sulfhydryl groups (-SH) that can strongly bind with Hg2+, leading to less efficient vapor generation and reduced AES signals of Hg2+. However, OPs like MP inhibit BChE activity and suppress TCh generation, resulting in the recovery AES signals. Ultra-trace levels of MP can be indirectly detected due to the high sensitivity of Hg2+ analysis using the gold filament enrichment PD-AES system. Under optimal conditions, the limit of detection (LOD) for the MP assay was 13 ng mL-1 within a range of 0.5 to 10 μg mL-1, with a relative standard deviation (RSD, n=5) of 0.8%. This analytical approach has proven effective in the detection of MP in TCMs, with advantages including ease of use and affordability.

Abstract:TC4 titanium alloy is a representative α + β dual-phase titanium alloy, which is widely used in engine blades and other components of aerospace equipment. This material typically requires heat treatment for strengthening to optimize its performance. To ensure that the heat-treated parts achieve ideal performance, it is necessary to test their physicochemical properties after heat treatment, such as microstructure, hardness, and elemental composition. To develop a rapid in-situ detection technology for the physicochemical states of heat-treated metal parts, a classification model was proposed by combining laser-induced breakdown spectroscopy (LIBS) with independent component analysis (ICA) and a deep neural network (DNN). The microstructure, Vickers hardness, and spectral characteristics of TC4 titanium alloy samples with different aging grades were analyzed. The spectral signals were preprocessed using the ICA method, and the results were used to establish a DNN model. The classification performance of the model was verified and evaluated using indicators such as the confusion matrix. The results show that the microstructure of TC4 samples can be regulated through solid solution and aging treatment, and the mechanical properties change accordingly. The uneven distribution of sample elements during microstructure control and the difference in ablated mass caused by different sample hardness contributes to the distinguishability of LIBS spectra of TC4 samples. The established ICA-DNN model facilitates dimensionality reduction and sensitive feature extraction of the physicochemical properties from the spectral data. Comprehensive evaluation results indicate that the classification performance of the model is strong, demonstrating the feasibility of using LIBS to characterize the physicochemical state of heat-treated metal materials. Compared to traditional detection methods, LIBS technology, as an emerging frontier detection technology, offers significant potential for in-situ, real-time, and micro-loss quality monitoring of heat-treated materials in industrial applications.

Abstract:Laser-induced breakdown spectroscopy (LIBS) has been successfully applied to various fields since its inception in the late twenty century. However, there are still challenges to overcome in order to enhance its performance in analytical experiments. These challenges include three major challenges: matrix effect, spectral interference, and self-absorption effect. This review specifically focuses on investigating the self-absorption effect, which disrupts the linear relationship between spectral line intensity and element concentration, thus affecting the the accuracy and sensitivity of LIBS analysis. The review explores different approaches to evaluate the extent of self-absorption, taking into account the evolutionary mechanism of this effect. Additionally, various methods for correcting spectra have been proposed, showing potential in significantly reducing self-absorption. Notably, the review emphasizes proactive measures to create non-self-absorbed conditions as the most effective approach to mitigate the self-absorption effect. Finally, the review presents a schematic description of exploiting self-absorption and highlights its promising prospects for future applications of LIBS.