Abstract:Although various methods have been developed for total organic carbon (TOC) analysis, most of them usually consume large amounts of samples, chemicals, and energy, thus making them only suitable for laboratory analysis. In this work, a new simple liquid electrode discharge microplasma-induced vapor generation (MPI-VG) was successfully developed to efficiently convert the organic compounds contained in water into CO2 on a microfluidic chip. Consequently, the generated CO2 was separated from the liquid phase and further swept into a miniature point discharge optical emission spectrometer (μPD-OES) for the detection of total organic carbon (TOC) in water samples via monitoring the carbon atom emission at 193.0 nm. Under optimal conditions, a limit of detection of 0.15 mg L?1 (as C) was obtained for TOC with a relative standard deviation better than 3.7%. The system is environmentally-friendly and efficient, which consumes only 43 μL of sample and 60 μg oxidant for each analysis. The total analytical time can be significantly reduced to one minute. The reaction mechanism was carefully investigated using quenching tests and gas chromatography. The practicality and anti-interference capabilities of the system were verified by measuring TOC in seawater and river water. Compared to conventional methods, this system demonstrates considerable potential for miniaturization due to the compact size of the microfluidic chip-based MPI-VG and μPD-OES.

Abstract:Space charge effects in the measurements by inductively coupled plasma mass spectrometry were investigated about groups 1, 2, and 13 of elements in the periodic table at various radio frequency (RF) power conditions and multiple extraction electrode-1 voltage conditions. Increased suppression of signal intensities was observed at an RF power over 1.1 kW with the increase of RF power, which was majorly attributed to space charge effects due to the increase in 40Ar+ density. A stronger negative extraction electrode-1 voltage resulted in stronger space charge effects. The extent of space charge effects decreased with the increase in mass-to-charge (m/z) ratio of the elements. The RF power at 0.8 kW to 0.9 kW can be a candidate condition for the measurements of elements with an m/z ratio under 100 at relatively higher sensitivity with much less space charge effects.

Abstract:Oxygen isotopes provide crucial insights into abiotic and biotic processes. Modern geosciences increasingly demand the capability to concurrently obtain in-situ oxygen isotope ratios from multiple mineral phases within rock samples. However, this is often hindered by the absence of matrix-matched standards for all target minerals on the same sample mount. To address this issue, we conducted secondary ion mass spectrometry (SIMS) analyses to investigate the variation of relative instrumental mass fractionation (RIMF) between different phases across two consecutive sample switch sessions using a series of O-isotopic standards, including glass, quartz, calcite, monazite, zircon, olivine, and apatite. Our results for the first time demonstrate that the RIMF between any two standards remains consistent within typical SIMS analytical uncertainties across two consecutive mount switch sessions. This consistency of RIMF enables us to develop a novel "bridge crossing calibration" method. In this approach, a common "bridge" standard present in both the sample mount and standard mount is used to calibrate mount-to-mount bias. This approach, combined with a matrix-matched standard in the standard mount, allow us to obtain the IMF of unknown samples even when the sample mount lacks matrix-matched standards. Additionally, this method is time- and cost-efficient, minimizes the consumption of standard samples by reusing mounts containing multiple standards, and eliminates systematic deviations when measuring different minerals in different sessions. As such, it provides a universal and robust technique for oxygen isotope analysis using SIMS.

Abstract:Concentration of trace elements through TeCl4 volatilization in a flow reactor is presented for the first time and the potential of this approach for analysis was assessed. The method was developed for the multi-element analysis of high-purity Te. The matrix was volatilized through the reaction of Te with chlorine gas, which was obtained by the electrolysis of hydrochloric acid. The behavior of 61 trace elements during Te chlorination at 200–270 °С was studied. The maximum number of trace elements (39) quantitatively remained in the concentrate at a volatilization temperature of 240 °С. Trace element concentrations were analyzed using inductively coupled plasma optical emission spectrometry (ICP-OES). The limits of detection (LODs) of the 39 trace elements were 0.2–30 ng g–1. The possibility of reaching lower trace element LODs was demonstrated. For Ag, Cd, Mn, and Pd, the LODs were reduced by 3–25 times by using electrothermal atomic absorption spectrometry (ETAAS), with trace element LODs of 0.04–2 ng g–1. The precision of the matrix chemical volatilization procedure was evaluated using spike experiments. Recovery rates ranged from 80 to 119%. The analysis of a Te sample with unknown composition using ICP-OES and ETAAS methods after the proposed matrix chemical volatilization procedure gave comparable results to those obtained by ICP-OES without volatilization.

Abstract:Determining non-metallic inclusions content and distribution are essential to bearing steel as they play decisive role on the fatigue life and the number of non-metallic inclusions increases when the steel size increases. The existing analysis methods have certain limitations with accurately quantify when it comes to analyzing inclusions in oversize metal. Based on the technique of Spark Mapping Analysis for Large Sample (SMALS), the Generalized Pareto After Normal Distribution Method (GPAND) has been developed to allow for the determination of the inclusions’ distributions of oversize metallic materials. This study presents the first evidence of using the generalized Pareto distribution's statistical function to analyze the spectral signals of non-metallic inclusions, employing peak fitting to merge the Normal and Generalized Pareto functions for assessing the spectral intensity of elements derived from high throughput spectral mapping technology. With GPAND method, the content and distribution of Al-inclusions and MnS inclusions are determined in the large size of bearing steel. It showed that the number of Al inclusions in sample 2-1 is higher than that in sample 2-2 and easily enriched towards the central region of the longitudinal section during solidification. The MnS inclusions in both samples are mostly located in the middle area of the longitudinal section and 1/4 L away from the edge. MnS inclusions in sample 2-2 is higher than that in sample 2-1. The evaluation of inclusion distribution can provide essential guidance for the production of ultra-clean and highly homogeneous metallic materials.

Abstract:This paper presents a novel mechanistic explanation for microwave-assisted LIBS to mitigate self-absorption effects. A set of plasma characteristic equations in cylindrical coordinates, including plasma isothermal expansion and modified adiabatic expansion kinetics equations, were formulated. These equations were subsequently coupled with microwave electric field equations to develop a microwave energy-assisted model. These models were employed to numerically analyze the plasma dimensions, velocity, and spatial distribution characteristics of plasma concentration, as well as the energy consumption during plasma expansion and the microwave-assisted energy. This analysis aims to explain the self-absorption mechanism and uncover how microwave-assisted LIBS mitigates self-absorption. LIBS experiments, both with and without microwave assistance, were conducted. An improved Saha-Boltzmann planar method was proposed to quantify the degree of self-absorption in the spectral lines of Al, Si, and Ca. Based on the measured spectral data, the plasma temperature of Al was calculated using this improved method, while the electron densities of Si, Ca, and Al plasmas were determined independently of self-absorption effects, as no spectral line intensity information was involved. The evolution of plasma expansion was captured using an intensified charge-coupled device (ICCD). The experiments confirmed that microwave-assisted LIBS did not alter plasma electron temperature or electron density, but provides sufficient energy for uniform plasma expansion, thereby reducing self-absorption. This finding offers a theoretical reference for mitigating jitter following femtosecond laser wire formation. Furthermore, the experiments demonstrated that microwaves effectively reduce self-absorption and enhance spectral intensity, validating both the accuracy and feasibility of the plasma characteristic equations and the microwave energy-assisted model. These results provide theoretical guidance and experimental optimization for plasma characteristics in LIBS applications.

Abstract:In this study, we present the novel use of a microwave digestion system (CEM BLADE) to digest geological materials for Re-Os isotopic analysis. This technique employs quartz digestion vessels that are easy to clean and reusable, avoid the complicated steps of opening and sealing, and enable complete digestion of the samples within 30 min at high temperature (max. 310℃) and pressure (max. 700 psi). The microwave digestion system was used to digest samples of four ultramafic rock reference materials (GBW07101, GBW07102, GBW07291, and WPR-1a), one basalt reference material (BIR-1a), and one black shale reference material (SGR-1b). The Re-Os isotope measurement results for GBW07291, BIR-1a, and SGR-1b were in agreement with previously published values, and we are the first to report Re-Os isotopes for GBW07101, GBW07102, and WPR-1a. Therefore, this new microwave digestion system is a simple, efficient, reliable, and safe sample digestion method for prospective applications in Re-Os isotopic analysis.

Abstract:Tourmaline, a boron-rich mineral, serves as a robust tracer for fluid-mediated geological processes due to its chemical stability and resistance to environmental influence. Here, we present a novel data reduction scheme (DRS) LCG_B.py, integrated within the Iolite 4 program for in situ boron (B) isotope analysis of tourmaline to investigate fluid activities in subduction zones. The innovative approach enables direct observation of 11B and 10B signal variation during laser ablation, while treating the 11B/10B ratios of reference materials for calibration as a fitted timeseries curve (usually using Spline AutoSmooth), facilitating automated analysis and precise calibration of B isotope ratios across specified ablation interval. Based on this, a high-precision B isotopes analysis protocol achieving spot size below 30 μm with analytical uncertainty better than 0.5 ‰ (2sd) (except Schorl (NaFe3Al6[Si6O18](BO3)3(OH)4) of 0.7 ‰) was developed. Application of this method to tourmalines in ultrahigh-pressure (UHP) eclogites from the Dabie orogen showed positive δ11B values ranging from +4.7 ± 0.2 to +10.5 ± 0.3 ‰, derivation from B-rich fluids sourced from impure marbles. The findings provide refined constraints on fluid-mediated geological processes and enhance our understanding of the complex fluid-rock interactions in the continental subduction zones. The improved analytical protocol and data processing technique establish a powerful tool for future geochemical investigations of subduction zone dynamics.

Abstract:Deep-sea sediments are critical sinks for transition elements and rare earth elements (REE) in the modern ocean. The Cu-Fe-Zn isotopic composition of deep-sea sediments has emerged as an essential tool for tracing marine metal enrichment processes and biochemical cycles. However, significant differences in elemental composition exist between deep-sea sediments and traditional samples. The absence of targeted separation and purification processes, combined with the scarcity of corresponding reference materials for deep-sea sediments, may adversely affect the accuracy of analytical results. In this study, we selected a series of marine geologically relevant reference materials, including four self-developed REE-rich deep-sea sediment reference materials, as the research object to determine their Cu-Fe-Zn isotopic compositions. Building on prior work with AG-MP-1M resin for Cu, Fe, and Zn separation, we added an AG-1-X8 resin column for Co-rich deep-sea sediments, achieving complete Fe-Co separation with a stable, efficient method applicable to marine samples. The analytical precision of the Cu, Fe, and Zn isotopic compositions for all samples is better than ± 0.04% (2SD). We recommend that appropriate method and reference materials from this study be utilized for subsequent marine geological sample tests.

Abstract:Jiangmen Underground Neutrino Observatory (JUNO) under construction in China can determine the neutrino mass hierarchy and improve the precision of three oscillation parameters by one order of magnitude. The Online Scintillator Internal Radioactivity Investigation System (OSIRIS) of JUNO serves as a precursor detector of JUNO. As the polymethyl methacrylate (PMMA) vessel is in direct contact with liquid scintillator in the OSIRIS, its radiopurity level has to reach the radiopurity requirements. In particular, the radioactive isotopes 238U, 232Th, and 40K must be considered. In this study, an analytical technique using dry ashing procedure coupled with inductively coupled plasma mass spectrometry (ICP-MS) has been developed in the determination of radioactivity ultra-trace U, Th, and K in PMMA used as vessel material in the OSIRIS of JUNO. Three sample preparation methods, microwave digestion coupled with solid-phase extraction, pre-pressurized microwave digestion with single reaction cell under ultra-high pressure and temperature, as well as dry ashing, were compared. With the advantages of excellent limits of detection, low background and cost as well as less time-consuming, dry ashing was chosen as the final sample preparation method and successfully applied to determine ultra-trace levels of U, Th and K by ICP-MS in PMMA. Furthermore, due to the property of easily being ionized for K, cold plasma mode of ICP-MS determination was used to avoid the ionization interference. The condition of cold plasma for K analysis was optimized. The content of 238U, 232Th and 40K was calculated by the isotope abundance of 238U, 232Th, and 40K multiply by the content of U, Th, and K, respectively. The limits of detection of the method (MLODs) for 238U, 232Th, and 40K were 0.10, 0.21 and 0.09 pg g-1, respectively. The developed method was successfully applied to the determination of 238U, 232Th and 40K in two real samples. Sources of measurement uncertainty were analyzed, and measurement uncertainty of 238U, 232Th, and 40K in sample 2 was evaluated.