查看更多>>摘要：The presence of pesticide residues in food represents a significant threat to consumers, mainly due to their toxicity to humans. Evidence has even been found that determines the relationship between many diseases and deaths from ingestion, contact, or mishandling. The need to introduce controls on pesticide residues has become an issue of central concern to society, given the increasing knowledge about the potential dangers associated with the use of pesticides. So the objective of the present study was to evaluate and analyze the feasibility of using the laser-induced breakdown spectroscopy technique as a potential tool for the quantification of dimethoate and chlorpyrifos in green leafy vegetables. For this purpose, reference samples with powdered chard were made using the aforementioned pesticides, with increasing concentrations in a range of 0-80 mg kg~(-1) and 0-250 mg kg~(-1), respectively. By applying calibration curves, it was possible to quantify pesticide residues by measuring S (416.26 nm), P (460.21 nm), and CI (837.59 nm) emission lines, with limits of detection of 1.7 mg kg~(-1), 0.8 mg kg~(-1), and 6.9 mg kg~(-1) respectively. Clear evidence of the applicability of this technique as a potential tool for the study of pesticides in food matrices was established. It was achieved by minimum sample preparation, ensuring a rapid analysis, low application costs, and without toxic waste production. In this way, its use as a preliminary evaluation technique or complementary to the analytical methods traditionally already used is evidenced.
查看更多>>摘要：We report on combining the surface analysis technique of Laser-induced Breakdown Spectroscopy (LIBS) with Raman spectroscopy. The combination of both techniques enables to study the chemical composition of the sample in a broader context when combining elemental and molecular information. Obtained elemental and molecular spectra are characteristic for individual biological samples (e.g., organs and cells) and are considered as a fingerprint. In this study, Raman spectroscopy is used for the detection of important molecular complexes in selected wood samples, e.g., accurate lignin and cellulose content on distinct spots of the sample surface. We chose Raman as a standard reference technique that is used for the lignin/cellulose ratio estimation. To complement the molecular information, LIBS technique was employed for the imaging of essential nutrients, e.g., Ca, Na, and K. Consequently, the contribution from both analytical techniques was combined and changes in the molecular content were visually correlated to the abundance of nutrition elements and show a direct dependence between the two signal responses. Thus, we can get specific answers to relation of lignin and cellulose formation with nutrients within the plant tissue. This evidence may then be helpful for the study of the effect of various environmental and stress factors.
查看更多>>摘要：The chromium and copper contamination of algae on a filter was directly monitored with laser-induced breakdown spectroscopy (LIBS) as a demonstration of LIBS capabilities. Liquid samples of the green alga Des-modesmus subspicatus were intentionally contaminated with chromium, incubated, filtered, and the filters with the algae were analysed. Inductively coupled plasma mass spectrometry (ICP-MS) was used as a reference method. One half of the filter with the algae was dissolved and analysed as a solution with ICP-MS and the second half was subjected to the LIBS and laser ablation-ICP-MS analysis. Chromium and copper were attributable to the algae contamination and detectable with LIBS. The results from the LIBS provided almost equivalent information about the relative changes of the Cr and Cu concentration in the algae. The sensitivity of LIBS with a Czerny-Turner spectrometer was fully comparable with the ICP-MS procedure. The trends from LIBS were more similar to the LA-ICP-MS ones. It means that the algae growth inhibition in dependence on the chromium or copper content can be alternatively monitored with LIBS instead of the complicated decomposition procedure in ICP-MS analysis.
查看更多>>摘要：In this work we studied the temporal evolution of the resonant emission lines of neutral silver (Ag I) at wavelengths 328.9 run and 338.2 ran, in different surrounding media (He, Ar, Xe and air) and at different laser pulse energy (15 mJ, 30 mJ and 60 mJ), using a frequency triplicated Nd:YAG laser (355 nm). We observed that the self-reversal of the Ag lines, caused by the combined effect of self-absorption and plasma inhomogeneity, is strong when the plasma expands in molecular gases (N2 and O2 in air) while is negligible in atomic noble gases (He, Ar, Xe), independently on the mass of the atoms. From the experimental data, we also conclude that the shock wave generated during the breakdown may play an important role in generating the plasma inhomogeneities which are essential conditions for the occurrence of the self-reversal effect.
查看更多>>摘要：During the last decade, various machine learning methods have been applied to improve the accuracy of quantitative analysis in laser-induced breakdown spectroscopy (LIBS) by modelling the complex relationship between spectral intensity and analyte concentration. However, machine learning methods tend to have high model complexity and are difficult to interpret their predictions. Moreover, their decision-making mechanisms rarely consider the physical principles behind quantitative analysis, resulting in a reduction of LIBS quantification accuracy and a question of trust in the quantification results. This work investigates the feasibility of incorporating domain knowledge into machine learning to improve LIBS quantification performance. A new regression method based on dominant factor and kernel extreme learning machine is proposed, namely DF-K-ELM. It uses knowledge-based spectral lines, related to analyte compositions, to construct a linear physical principle based model and adopts K-ELM to account for the residuals of the linear model. DF-K-ELM intuitively explains how knowledge-based spectral lines influence prediction results and improves model interpretability without reducing model complexity. The proposed method, DF-K-ELM, is tested on 10 regression tasks based on 3 LIBS datasets and compared with 6 baseline methods. It achieves the best and second best performance on 4 and 2 tasks, respectively. Moreover, compared to traditional machine learning methods, dominant factor based methods yield higher accuracy in most cases. Such results demonstrate that incorporating domain knowledge into machine learning is a viable approach to improve the performance of LIBS quantification.
查看更多>>摘要：We investigate femtosecond laser-induced plasma spectroscopy (fs-LIPS) of water, and find that at different input laser energies the measured characteristic/s-LIPS emissions from trace metal elements in water exhibit different dependences on the chirped pulse duration. As the pulse is temporally stretched from 50 fs to longer durations up to 500 fs, the emission intensity from Al I on the 3s~24s~ 2S_(1/2) → 3s~23p~2S_(1/2,3/2) transitions experiences three typical variation regions, i.e., the increasing, plateau, and decreasing regions, respectively, but their temporal range varies as a function of the input laser energy. By comparing with the optical emissions of fs-LIPS of different materials including ambient air, solid metal Aluminum, and the two semiconductor materials with different bandgaps, i.e., silicon and sapphire, we ascribe the observed dependence of fs-LIPS emission of trace Al element in water on the pulse duration to the tradeoff between the strong field ionization (SFI) and the subsequent avalanche ionization (Al), both of which are determined by the wide bandgap semiconductor property of water.
查看更多>>摘要：The excitation of Ni I and Ni II emission spectra in an argon glow discharge was analyzed and compared with that of some other transition elements. Higher Ni I levels are enhanced compared to the trend corresponding to the Boltzmann distribution. Selective excitation of some Ni II levels was observed and attributed to the (Ar~+-Ni~0) charge transfer reaction.
查看更多>>摘要：Arsenic determination by LIBS at low levels is a challenging analytical task due to its low sensitivity, limited number of available emission lines, and spectral interferences. In this work, a LIBS system with controlled atmosphere for the determination of arsenic at low concentrations in copper ores is presented. Under optimized conditions, the As lines at 278.06 nm (with interference of Fe II) and 286.04 nm were able to be used for measurements. Improved analytical figures of merits were obtained using deconvoluted spectra and artificial neural network based on a radial basis function (ANN-RBF), specific values of relative error percentage (REP %), root mean square error of prediction (RMSEP) and intervals of limits of detection (LOD) and quantification (LOQ) were 18.6 wt%, 0.037 wt%, 0.045-0.062 wt% and 0.135-0.185 wt%, respectively.
查看更多>>摘要：Probe diagnostics is used to determine the electron temperature and electron number density in a low pressure inductively coupled plasma (ICP) ignited in the mixture of SiF4, Ar and H2. Emission spectra of mixtures with different stoichiometry of components are investigated and the electron density distribution function (EDDF) is estimated. The optimal conditions for high conversion of SiF4 into Si are found by studying the dependence of the yield of silicon upon the ratio of reagents. The maximum achieved yield of silicon is 85% under the optimal conditions. Based on the analysis of IR and MS spectra of exhaust gases, 5% of initial SiF4 converts into volatile fluorosilanes. A rate of production of Si is 0.9 g/h at the energy consumption 0.56 kWh /g.
查看更多>>摘要：We report the accurate quantitative measurements of the photoionization (PI) cross section of lithium-7 confined in a magneto-optical trap (MOT). The losses from the MOT induced by radiation of the low-power light-emitting diodes (LEDs) are measured as a function of the photoionizing radiation intensity. On the basis of these measurements, the PI cross section from the 2P_(3/2) excited state of lithium is evaluated for three different LEDs. The PI cross sections of lithium from the 2P_(3/2) state at 259, 280, 307 run are determined to be (5.4 ± 0.4), (8.1 ± 0.8) and (9.5 ± 1.1) Mb respectively. Accuracy of our measurements is better than that of previous reported results. The semiclassical calculations taking into account the fine structure of the first excited state of lithium are performed. Our values are in good agreement with experimental results earlier reported and are consistent with the theoretical data.
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