Abstract:Distinguishing biomineralized minerals from inorganic minerals has been a longstanding challenge. The organic matter within biomineralized minerals constitutes compelling evidence that sets them apart from inorganic minerals. However, for small samples that have undergone degradation and diagenetic alteration, routine analytical technologies have difficulties in identifying internal residual organic signals. Atom Probe Tomography, as the highest-spatial-resolution microanalytical technique, facilitates the study of elements spatial distribution and nano-scale structures, holding significant potential for applications in biogeochemistry. In this study, Atom Probe Tomography has been applied to fossil samples for the first time, comparing inorganic Durango apatite with fossil conodont. This research discovered residual organic components within conodont, manifesting in the form of nano-scale particles coupled with high carbon and nitrogen concentrations. This signal is promising for differentiating between biominerals and inorganic minerals, which is greatly potential for identifying nano-scale biosignatures in ancient samples.

Abstract:The composition of particles resulting from pulsed laser ablation is not well understood, although it is anticipated that molecules from the ablated material undergo varying degrees of breakdown, depending on factors such as laser wavelength, energy, pulse width, matrix properties, and gas atmosphere. As reliable arsenic characterization and speciation techniques are available, a fundamental study was undertaken to shed light on the behavior of arsenic compounds (arsenic pentoxide, dimethylarsenic acid, and arsenobetaine within a cellulose matrix, along with pure elemental arsenic), using a pulsed 213 nm Nd:YAG laser and ablation in different gas atmospheres (He, Ar/CO2 [99/1 %], Ar/O2 [80/20 %], and O2) at atmospheric pressure. The generated arsenic, collected in aerosol form on inline syringe filters (0.2 μm), was subjected to sequential dissolution, yielding water-soluble, HCl-soluble, and insoluble fractions. The water-soluble fraction was analyzed for arsenic species using chromatographic techniques in combination with element-specific detection. The analysis revealed that extremely complex processes take place during laser ablation, not only (partially) stripping organoarsenic species from their methyl groups and lowering the valence state, but also creating conditions for the synthesis of methylated arsenic species from arsenic pentoxide and generating more or less soluble nano/micro/macro particles for all arsenic compounds. These findings contribute to a more nuanced understanding of the multifaceted photochemical transformations that may occur during laser ablation of molecules.

Abstract:The handheld laser-induced breakdown spectroscopy (LIBS) device has been developed to evaluate the aging grade of T91 heat-resistant steel. However, the reduced size of the device could potentially affect the accuracy of the measurement. To overcome this challenge, a novel spectral preprocessing approach that combines Lorentzian fitting correction and extended Kalman filter with support vector machine (SVM) is proposed in this work to enable the reliable evaluation of T91 aging grade by a handheld LIBS. The spectral features of T91 samples were measured and revealed that the obtained spectral line broadening is mainly due to Stark broadening. Consequently, the independent spectral peaks in the spectra can be corrected with Lorentzian function to obtain more comprehensive spectral information. Afterwards, the extended Kalman filter is introduced to further correct the measured spectral data, diminishing the fluctuation in the spectral signal and the device noise during the measurement. The results show that the accuracy of the T91 aging grade classification model based on the new preprocessing method can achieve 94 %. This surpasses the accuracy of the models developed with standard normal variation (SNV) and multi-scatter calibration (MSC) preprocessing methods. The proposed method improves the accuracy of handheld LIBS for T91 aging grade classification and provides a new insight into improving the quality of LIBS spectral data.

Abstract:A combination of trace elements preconcentration and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) is proposed for the analysis of high purity substances. The analytical figures of merit of this combination were evaluated using high purity germanium dioxide as an example. Trace elements were preconcentrated by germanium volatization in the form of germanium tetrachloride from sample solutions. The trace elements concentrate was evaporated to dryness on the surface of a high-purity silicon substrate and analyzed by LA-ICP-MS. Indium was used as an internal standard to obtain quantitative data. Limits of detection (LODs) for 47 trace elements are in the range from 0.3 to 300 ppt wt (0.3 to 300 pg g-1). The obtained LODs are 10-100 times lower compared to ICP-MS analysis of germanium with preconcentration of trace elements. The accuracy of results was confirmed by comparing with results obtained by the traditional ICP-MS analysis of the trace elements concentrates and by the “spike” experiments.

Abstract:This study demonstrates an analytical method for the high spatial resolution (20 μm) and high-precision determination of antimony (Sb) isotope composition in stibnite, using femtosecond laser ablation multi-collector inductively coupled plasma mass spectrometry (fs-LA-MC-ICP-MS). The potential matrix effect-inducing elements in Sb isotope composition measurements exhibit extremely low concentrations in two newly introduced natural stibnite reference materials, DC and BJS, rendering their impact virtually negligible during fs-LA-MC-ICP-MS analysis. Through reciprocal correction of DC and BJS, consistent results were achieved, aligning with those obtained by SN-MC-ICP-MS, indicating an absence of discernible matrix effects between the two samples. A comprehensive assessment was conducted to evaluate the contribution of the Sn standard solution to enhance the external precision of measurements. The 2SD of δ123Sb mean values increased by 0.02‰ to 0.04‰. Adjusting the laser ablation spot size (5μm-80μm) to control signal intensity, we investigated the deviation in δ123Sb caused by mismatched signal intensities between the sample and the reference material. The matching range of signal intensity between the reference sample and the test sample was within -40% to 140%, ensuring satisfactory precision. Additionally, once the signal intensity of 121Sb exceeded 15V, the internal precision of the 123Sb/121Sb ratio no longer exhibited a significant decline. Measurements of DC and BJS were conducted using fs-LA-MC-ICP-MS, coupled with SN-MC-ICP-MS, backscattered electron maps (BSE) and elemental compositions, confirming the accuracy of this method and the homogeneity of the two potential reference materials.

Abstract:Layered double hydroxides (LDHs) are a class of materials that may be readily synthesized in a laboratory environment. This work successfully conducted the synthesis of a new nanomaterial (ZnMnAl LDH). The characterization of this material was accomplished utilizing many analytical techniques, including FTIR, XRD, SEM-mapping, and FE-SEM. ZnMnAl LDH was employed to separate and enrich Cu(II) and Ni(II) from soil and water samples. The Cu and Ni ions were eluted from ZnMnAl LDH nanoparticles by using 2 mL of 0.1 mol L?1 of HNO3. The metal ions were quantified using flame atomic absorption spectrometry (FAAS). An investigation was conducted to examine the impact of many analytical factors on the efficiency of metal ions' extraction. These parameters include pH, sorbent amount, eluent volume, eluent concentration, sample volume, and possible interfering ions. The detection limits for Cu(II) and Ni(II) were found to be 0.74 and 0.52 μg kg?1, respectively. In addition, the relative standard deviation (RSD%) for Cu(II) is 3.8 and for Ni(II) is 1.9. The linear range for both analytes is 50–1000 μg L?1, and the preconcentration factor is 15 for both. The method’s validation was verified by the analysis of certified reference materials, namely BCR-505 estuarine water and GBW07429 (GSS-15) soil. For soil samples, Ni(II) and Cu(II) concentrations vary from 9.8 to 62.8 mg kg-1 and 9.9 to 73.5 mg kg-1, respectively. The technique described was used to quantify minute concentrations of copper (Cu) and nickel (Ni) in samples of both natural water and soil.

Abstract:Determination of minor elements is the weakness of one-point calibration laser-induced breakdown spectroscopy (OPC-LIBS), which greatly hinders the further development of OPC-LIBS. The normalization in minor elements determination is seriously influenced by self-absorption effect of matrix element in laser-induced plasma. In this work, a modified self-absorption correction method was proposed in OPC-LIBS. The plasma temperature was determined by the slope of Saha-Boltzmann plots established for minor elements, and the electron number density was calculated from the Hα line. The internal reference line of the matrix element was corrected and iterated, until the maximum value of the self-absorption coefficient in the analytical line of minor elements was less than 1. The correction factors were determined based on elemental concentration in the reference sample and Boltzmann plots, and then were used in other samples for elemental determination. Twelve certified 6061 reference aluminum alloy samples and seven micro-alloy steel samples were used as examples for demonstration. Compared with both conventional OPC-LIBS and IRSAC & OPC, the dist in the proposed method (modified IRSAC & OPC) was reduced to 0.537-1.632 wt.% and 0.891-2.805 wt. % for the aluminum alloy and micro-alloy steel, respectively. These results showed that the proposed method can improve the accuracy of detecting minor elements using only one reference sample, which greatly facilitates the application of LIBS.

Abstract:To study the change of chromium speciation in the Cr(VI) natural attenuation processes, which involve both the diffusion and redox reaction of Cr(VI), Cr(VI) diffusion-reaction experiments for carbonate rock samples were conducted. The synchrotron radiation μ-XRF and SEM-EDS mapping revealed that in organic-rich carbonate rock samples, fresh precipitated Cr was mainly located near the surface and associated with organic matters. Whereas, in the sample with low organic matter, Cr was distributed evenly. These results indicate that the organic matter in the fractures and pore space is the major natural reductant that reacts with Cr(VI) in organic-rich samples, and forms reducing products (Cr(III) precipitates), which might aggregate and block the pore throats, and prevent further diffusion of Cr(VI) into the rock matrix. The synchrotron radiation X-ray absorption near-edge structure (XANES) was used to obtain the distributions of Cr chemical forms. The results show that for organic-rich samples, the Cr(OH)3 fraction in the center was higher than that on the surface, whereas, for the samples containing low organic matter, no such significant difference was found. One possible explanation for these findings is that in organic-rich carbonate rock samples, the Cr(III) hydroxides, which aggregate in the zones near the surface, might age and transform from crystalline to the stable chemical forms of Cr(III) oxyhydroxide or even Cr(III) oxides, which could enhance the effect of Cr(VI) natural attenuation process. This work provides a feasible way to investigate the change of chromium chemical speciation during its diffusion-reaction processes in rock samples using synchrotron radiation techniques.