Spectrochimica Acta Part B: Atomic Spectroscopy最新文献

One of the most versatile and effective methods to improve LIBS analysis of liquids is Thin Film Microextraction (TFME).

This approach generally uses carbon-based adsorbent films to extract analytes from a liquid sample and bind them into a solid matrix, which is ideal for LIBS. In a previous work, we demonstrated the feasibility of TFME supports based on graphene prepared by Pulsed Laser Ablation in Liquid (PLAL) for LIBS analysis.

In this paper, we optimized the preparation of such supports for the analysis of heavy metals in aqueous samples (i.e. chromium, lead and nickel), by analyzing both standard solutions and real samples. The feasibility of coupling TFME with NELIBS approach was also exploited. The procedure was applied to the analysis of both mineral water and well water samples.

We obtained a standardized procedure for the extraction of three analytes (Pb, Cr and Ni) and estimated LOD values in spiked mineral water of the order of 0.6 mg/L for LIBS and 0.2 mg/L for NELIBS.

A combination of optogalvanic spectroscopy and laser-induced fluorescence spectroscopy with a continuous wave tunable single mode Ti-Sa laser was applied to find new energy levels of atomic holmium. Free and excited holmium atoms were produced in a liquid nitrogen-cooled hollow-cathode lamp. In this study, we examined 35 spectral lines of Ho I in the near-infrared wavelength range from 698 nm to 833 nm. Altogether, 16 new energy levels have been discovered, 5 levels of even parity and 11 levels of odd parity. Another four energy levels have been discovered but have already been published by another research group. Data on the hyperfine structure for the new levels are presented. Additionally, hyperfine structure data of three known levels of even parity were determined for the first time. The existence of the new energy levels was confirmed by analyzing 60 lines of previously measured Fourier transform spectra to precisely determine the energy of the levels.

The presence of bacterial cells from three species has been detected in clinical specimens of human urine using laser-induced breakdown spectroscopy (LIBS) by using a partial least squares discriminant analysis (PLS-DA) of 360 spectra obtained from 12 specimens of infected urine and 239 spectra obtained from eight specimens of sterile urine. Nominally sterile urine specimens obtained from four patients at a local hospital after being screened negative for the presence of bacterial pathogens were spiked with known aliquots of Escherichia coli, Staphylococcus aureus, and Enterobacter cloacae to simulate clinical urinary tract infections. Fifteen emission line intensities measured from the LIBS spectra and 92 ratios of those line intensities were used as 107 independent variables in the PLS-DA for discrimination between bacteria-containing specimens and sterile specimens. The PLS-DA models possessed a 98.3% sensitivity and a 97.9% specificity for the detection of pathogenic cells in urine when single-shot LIBS spectra were tested. To increase the signal to noise ratio, thirty spectra acquired from a single specimen were also averaged together and the averaged spectra were used to construct a model. When each averaged spectrum was withheld from the model individually for testing, the diagnostic test possessed a 100% sensitivity and a 100% specificity for the detection of bacterial cells in urine, although the number of test spectra was necessarily reduced.

The entire LIBS spectrum from 200 nm – 590 nm was input into an artificial neural network analysis with principal component analysis pre-processing (PCA-ANN) to diagnose the bacterial species once detected. This PCA-ANN test possessed an overall sensitivity of 97.2%, an overall specificity of 98.6%, and an overall classification accuracy of 97.9% when using 80% of the data to build a model and withholding 20% for cross-validation testing. The PCA-ANN was also performed on each of the 12 bacteria-containing filters individually, using the other 11 filters to build the model. The average sensitivity of this test, calculated by averaging the sensitivities measured for each of the three bacterial species, was 70.9% and the average specificity was 85.5%. Based on these results, the average classification accuracy for the test when used to discriminate between the three microorganisms was 80.6%. These results indicate the potential usefulness of LIBS for rapidly detecting and possibly diagnosing urinary tract infections in a clinical setting.

We report on the absolute frequency determination of the 5s5p ${}^1{P}_1$ - 5s5d ${}^1{D}_2$ transition in atomic strontium, achieved through frequency comb-referenced laser-induced-fluorescence (LIF) spectroscopy. We excite the $5s^2$ ${}^1{S}_0$ - 5s5p ${}^1{P}_1$ transition using an on-resonance laser at $\approx$461 nm, and then measure the variation in the LIF signal while scanning the laser at $\approx$767 nm across the 5s5p ${}^1{P}_1$ - 5s5d ${}^1{D}_2$ transition. We determine the absolute frequency of $390599571.7\pm 0.4$ MHz, with an accuracy that surpasses the previous most accurate measurement by two orders of magnitude. This measurement technique can be readily applied for precision spectroscopy of high-lying states not only in strontium, but also in other atomic species.

To meet the demands of in situ analysis, a fiber-optic laser-induced breakdown spectroscopy (FO-LIBS) system was established to predict the elemental concentrations and pyrolytic parameters. The key parameters, including pulse energy, gate delay, type of surrounding gas, and flow rate of gas, were optimized to improve the signal-to-noise ratio of the spectral lines, and the evolution characteristics of the plasma morphology in different gas atmospheres were investigated. Under the optimized experimental conditions, C, H, Si, Ca, Fe, and Mg were calibrated using pellet samples based on partial least squares regression, and the average relative prediction error of the natural samples was lower than 10%. In addition, the support vector regression method was utilized to predict pyrolytic parameters such as TOC, Pg, and T_max with the R² of all calibration curves being higher than 0.97. The abundance and generation potential of hydrocarbons were evaluated using the predicted TOC and Pg, and T_max could contribute to the thermal maturity of the kerogen.

Microwave induced plasma atomic emission spectrometry (MP-AES) was evaluated as a strategy for the analysis of simulated gastrointestinal solutions to estimate the in vitro bioaccessibility of essential elements in cooked pink shrimp. Operational conditions such as pump speed, nitrogen flow, and viewing position were thoroughly optimized for each element. Afterwards the validation of the analytical method was performed. Limits of quantification ranged from 0.005 mg kg⁻¹ (Mn) to 0.106 mg kg⁻¹ (Zn). Accuracy was evaluated by using a certified reference material and performing a mass-balance study. Suitable mass balances within the range 95–105% were obtained. In vitro bioaccessibility in cooked shrimp samples ranged from 14.7% (Fe) to 48.1% (Zn), in agreement with previous data from other shrimp species. The proposed procedure proved to be an outstanding sequential analytical strategy for elemental bioaccessibility studies, providing simplicity and high sample throughput compared to conventional approaches. Furthermore, this work constitutes the first work regarding the optimization of an elemental bioaccessibility study on animal protein employing MP-AES.

Despite the detection of fixed nitrogen in meteorites and directly on Mars' surface, the abundance and distribution of nitrogen sequestered in the martian crust remains unknown. Given that nitrogen is a bioessential element that is required for the synthesis of amino acids, nucleic acids, and other organic molecules vital for life, this gap in knowledge is one of the most important challenges in constraining martian habitability. Laser-induced breakdown spectroscopy (LIBS) has the capability to detect N in natural rock samples and is available as a stand-off survey instrument on multiple currently active Mars rovers, creating an immediate opportunity to map the stratigraphic distribution of N within diverse depositional settings. However, little has been published regarding the detection of N with LIBS.

To lay a foundation for N detection on Mars using LIBS, we synthesized a comprehensive suite of samples with variable amounts of nitrogen (as nitrate or ammonium) in either a Mars regolith simulant or a clay matrix. We present baseline spectra of N emission in Mars-relevant matrices and identify spectral interferences. Our results indicate that 17 diagnostic N emission lines are reliably detectable from mineral-bound N against a basaltic background, but only four lines exhibit sufficient sensitivity to be detected across a range of N concentrations and within all tested matrices. To elucidate optimized strategies for quantification, we present an iterative series of PLS models. We find that prediction accuracy is improved by restricting the compositional range of the training set, normalizing the data, subtracting baseline continuum emission, and simultaneously modeling the emission behaviour of multiple diagnostic N lines at once. We observe that the prediction uncertainty increases (worsens) from 8.4% to 29.9% if models are used to predict N in samples with a dissimilar matrix than those used during training, suggesting poor generalizability outside the training range. Consequently, future work should focus on developing a larger, more diverse training set that encompasses the range of N concentrations and phases expected to be encountered on Mars, which may be used to train generalizable models. Overall, this work demonstrates that LIBS is a promising tool for determining the abundance of N sequestered in martian surface materials and lays a foundation for future development.

This study presents a detailed picosecond LIBS analysis of WTa coatings on Molybdenum substrate with varying layer thicknesses for fusion relevant applications. Ps-LIBS is performed on three WTa layers; two without deuterium ($\sim$7 μm thickness) and one with deuterium ($\sim$1 μm thickness). The LIBS measurements are conducted under argon gas flow at $5\pm 0.2$ mbar pressure with different laser pulse energies (1 mJ, 3 mJ) and 100 spectra are recorded consecutively at one spot on the sample for different set of gate delay/gate width (200/200 ns, 300/300 ns, 450/450 ns). The obtained LIBS and Glow-Discharge Optical Emission Spectroscopy (GDOES) depth profiles are compared with the confocal microscopic measurements showing good agreement. Additionally, the ablation rate and layer thickness are calculated for different experimental conditions. The Calibration-Free LIBS approach is used for elemental analysis and the results are compared with GDOES results. The capability of ps-LIBS to quantify Ta in WTa alloy is explored for 2 at.% of Ta. However, due to higher ablation rate of laser and thin coating in WTaD sample, the layer is irradiated in few laser pulse and therefore, CF-LIBS analysis is not performed for it.

Soil, one of the most precious natural resources on Earth, gradually accumulates heavy metals, inevitably causing significant damage to the ecological environment. Here, we introduce confocal controlled laser induced breakdown spectroscopy (CCLIBS) technology for the quantitative analysis of the heavy metal cadmium in soil for the first time. CCLIBS offers better spatial consistency and stable plasma temperature during sample ablation compared to traditional LIBS, thereby reducing matrix effects to improve the accuracy of the quantitative results. The fluctuation of the spectrum and limit of detection are reduced by 0.6 times and 0.39 times, respectively. An effective prediction model was established using the partial least squares method, with a determination coefficient increased to 0.96. The root mean square error of prediction and average relative error are reduced to 67.67 and 0.20, respectively. These results indicate that CCLIBS provides consistent ablation conditions for elemental quantification and yields reliable test results, which is significant for monitoring heavy metals in the ecological environment and effectively intervene and mitigate environmental contamination.