Applied Spectroscopy最新文献

This contribution presents a novel, simple and cost-effective method for observing the movement of reaction products out of the plasma-liquid interface (PLI). By employing an imaging spectrograph, a multidimensional view, i.e., spatial, spectral, and temporal, of reactions occurring at the PLI is made possible, including the ability to track the reactions from the interface to bulk. Ultraviolet-visible (UV-Vis) absorption spectroscopy techniques are key for interpreting changes in the observed section, and these techniques allow for calculating concentrations, determining production rates, and identifying reaction pathways. We describe and specify a direct vision imaging spectrograph and demonstrate its application to the aforementioned task. This approach provides valuable insight into the dynamics at the PLI and is a promising method for studying reaction kinetics and mechanisms in similar systems. Imaging spectroscopy is a valuable tool for analyzing the spatial, spectral, and temporal dynamics of plasma-liquid interactions. Our findings provide new insights into the complex physical and chemical processes which occur in such systems; they offer a deeper understanding of plasma-induced phenomena at the liquid interface. As a consequence, this research furthers possibilities for optimizing plasma-driven chemical reactions.

Raman spectroscopy is a powerful characterization technique with increasing applications that would greatly benefit from data harmonization. Several standards deal with calibration in Raman spectroscopy, but no detailed procedure covers the complete calibration of an instrument, including both spectral axes, from reference material spectra generation to data processing. Moreover, the type of reference materials, the quality of the recorded spectra and the choice of the fitting functions are critical for obtaining precise and reliable reference data for calibration. This report describes the challenges and importance of peak fitting for Raman signal calibration based on an interlaboratory study with 10 different instruments. Spectra of neon emission, silicon, calcite, and polystyrene were fitted using common peak shapes, observing that Gaussian, Pearson IV, Voigt, and Voigt shapes are preferred for these materials, respectively. An analysis of the effect on the fitting of the signal-to-noise ratio (S/N) recommends a minimum value of 100 for a Raman peak if it should be used to calibrate a Raman instrument. Some factors that might affect the peak shape of the Raman signal, such as the physical and chemical properties of the sample, the nature of the electronic transitions, the instrument response and the spectral resolution are discussed. The results highlight the role of peak fitting analysis in improving the quality and reliability of Raman spectra calibration and, thus, enhancing data transfer and comparability, especially for handheld and portable Raman analyzers, as well as applications based on quantification, multivariate data analysis, and other complex processing steps.

Raman spectroscopy is an analytical technique of choice for Earth and planetary sciences, which was recently selected as part of robotic exploration missions on Mars. Indeed, several miniaturized Raman spectrometers have been included into the scientific payload of rovers for the remote surface exploration of Mars: SuperCam and Scanning Habitable Environments with Raman and Luminescence for Organics and Chemicals (SHERLOC) for the NASA Mars 2020 mission and the Raman laser spectrometer (RLS) for the European Space Agency's (ESA) ExoMars mission. In preparation for these missions, a number of Mars analogue biogeological samples retrieved on Earth are extensively interrogated using Raman spectrometers, including flight prototype instruments but not only. Some studies also used flight representative portable instruments, as well as benchtop instruments. Commonly, authors reported the excitation laser wavelength and its power but often omitted the laser spot size on the sample which is a key factor for comparing several studies in term of spectrometer capabilities. In this study, we reported an easy, fast and universal experimental approach for determining the effective laser spot size, defined as the diameter of the sample section which is effectively probed by the Raman spectrometer during the analyses. Here, we characterized the effective laser spot size for a benchtop micro-Raman system and two different portable spectrometers, using a standard silicon wafer and gypsum powders with various average grain sizes. The dependence of the laser spot size with the grain size of the samples is discussed with regards to qualitative and quantitative analyses of solid dispersions in the scope of remote planetary missions.

There is a need for in-field actinide measurements in support of nuclear forensic, safeguards, and environmental monitoring missions. Traditional methods of inorganic/elemental analysis, such as inductively coupled plasma mass spectrometry (ICP-MS), have high operational overheads, making these platforms ill-suited for this task. The liquid sampling-atmospheric pressure glow discharge (LS-APGD) ionization source is a proven microplasma ionization source with significantly reduced operational overhead as compared to ICP-MS; however, most studies to date have focused on coupling the LS-APGD to an ultrahigh resolution Orbitrap mass spectrometer. While the Orbitrap mass spectrometer is a benchtop instrument, it is quite complex with a large footprint and requires extremely low mass analyzer pressures. The Advion Expression^L compact mass spectrometer (CMS) is a compact, easily transported single quadrupole mass spectrometer platform that was previously coupled with the LS-APGD to measure multielement/metal solutions, albeit not actinides. To this end, this manuscript reports the optimization of the LS-APGD with the Advion Expression^L CMS mass spectrometer platform specifically for in-field actinide (uranium and thorium) measurements. This is the first report on the optimization of the dual-electrode LS-APGD on the CMS, including a modified ion sampling geometry. This also includes the first analysis of thorium using the LS-APGD, regardless of mass spectrometer coupling. After establishing that the LS-APGD and the mass spectrometer operations could be optimized independently, the LS-APGD discharge conditions were optimized with a design of experiments approach, with the mass spectrometer parameters optimized by a full factorial study. Once fully optimized, limits of detection of 0.2 ng total analyte mass were found for both uranium and thorium, below the EPA requirements for drinking water.

Chromosome characterization is crucial in cytogenetic research and diagnostics, necessitating precise imaging methods to ensure proper analyses. The aim of this project is to identify a reliable method for chromosomal characterization that uses hyperspectral imagery of stained metaphase chromosomes using bright-field microscopy. We analyzed four hyperspectral images of stained chromosomes acquired under bright-field illumination. To address the high dimensionality of the hyperspectral hypercubes, we applied five dimension reduction algorithms based on spectral band selection to determine the most effective approach. A comparative study was conducted between five band selection methods to assess their effectiveness in chromosome characterization. The results indicate that sparse subspace clustering and multi-objective band selection are the most effective methods, outperforming the others in reducing the spectral dimensionality of the hyperspectral data, while preserving key properties essential for accurate chromosomes characterization. This study demonstrates that careful selection of spectral bands can enhance the analysis of spectral hypercubes for chromosome characterization.

Complex-valued chemometrics utilizes both the absorption index and refractive index spectra. Through application of a Kramers-Kronig transformation, it can also be extended to absorbance and Raman spectra. In this work, we expand complex-valued chemometrics to include partial least squares (PLS) regression. Several strategies for implementing complex-valued PLS are explored. One approach builds on the nonlinear iterative partial least squares (NIPALS) formalism to compute real and imaginary components of the PLS solutions in parallel. Additionally, as both the real and imaginary parts can assume positive or negative values, this results in 2^N possible solutions for N components. In this case, the optimal solutions are selected using a brute-force approach combined with a nested leave-one-out (LOO) scheme. Additionally, single-value decomposition (SVD) can be directly applied to the complex matrix product of the spectral and concentration matrices. We compare these approaches using complex refractive index spectra of mixtures from the thermodynamically ideal systems benzene-toluene, benzene-cyclohexane, and benzene-carbon tetrachloride (CCl₄). In particular, when the high-wavenumber refractive index differs between the neat components, complex-valued PLS achieves errors more than an order of magnitude lower than conventional PLS based solely on the imaginary part.

Chromium-doped zinc selenide (Cr:ZnSe) crystals are the gain media of choice for mid-infrared lasers operating over a 1.9-3.4 µm spectral range. In this study, we used laser-induced breakdown spectroscopy (LIBS) of Cr:ZnSe polycrystalline materials to improve the sensitivity of detecting chromium concentration in the laser-active materials. The fundamental harmonic of a Q-switched neodymium-doped yttrium aluminum garnet (Nd:YAG) laser was used as an excitation source. After calibration of the LIBS signal, we calculated that chromium's limit of detection (LOD) was 30 parts per million (ppm). Normalization of the Cr(I) intensity peak at 357.9 nm by the square root of the Zn(I) peak at 636.2 nm reduced the LOD to 20 ppm and increased the coefficient of determination to R² ≈ 0.98. These results demonstrate the potential of LIBS for microscale mapping of dopant distributions in laser crystals and for on-site monitoring of material quality during fabrication.

Phthalate-based plasticizers in polyvinyl chloride (PVC) polymer were examined using infrared (IR) spectroscopy and evolved gas analysis-mass spectrometry (EGA-MS), a type of mass spectrometry (MS). IR signals arising from the C=O stretching vibrations of the plasticizers are observed but it is difficult to distinguish individual components due to their structural similarity. In contrast, temperature-dependent mass spectra of the PVC sample revealed a characteristic increase in total ion signals within the 100-220 °C range, indicating that plasticizer desorption occurs predominantly before decomposition of the PVC polymer. The application of two-dimensional correlation spectroscopy (2D-COS) to the mass spectra elucidated the detailed sequence of spectral changes during thermal desorption. The 2D correlation spectra derived from the mass spectra within the 100-220 °C range exhibited distinct correlation peaks associated with bis(2-ethylhexyl) phthalate, bis(2-ethylhexyl) adipate, and bis(2-ethylhexyl) sebacate. These results demonstrate that EGA-MS, combined with 2D-COS, can effectively identify individual additives in polymer systems.

In the first paper in this series, we proposed the use of a set of colored LEGO blocks as "standard" samples for the evaluation of fluorescence avoidance and mitigation schemes in Raman spectroscopy, as well as for use to evaluate the instruments' performance on dark samples. In the second paper we described the spectra obtained on the same blocks from ten different handheld Raman instruments. We found that the combination of a series of colored blocks (white, yellow, red, and blue), and successively darker tone blocks (white, gray, and black) do challenge these instruments and shed light on the ways that their manufacturers have optimized these instruments in specific areas and for different purposes. In this paper we extend the work using an advanced Raman data collection technique: A fast-repetition-rate, short-pulse, laser with a single-photon avalanche photodiode (SPAD) array detector capable of providing a time-sequence output, commonly known as a "time-gating" or "time-resolved" approach. The results are evaluated and compared to those in the first two papers. In addition, X-ray fluorescence (XRF) spectra were also collected to confirm identifications of some of the blocks' inorganic pigments, which were detected via their Raman spectra.

Optical identification of liquid droplets, aerosols, or thin films is critical for many applications. While reference spectra are sometimes available for such measurements, they are not always applicable to the observed spectrum or the given sample morphology. Reference spectra for many forms can be modeled, however, if the n/k vectors (real and imaginary refractive indices) are available. In previous work we have reported protocols to determine the n/k vectors for dozens of liquids, primarily in the mid-infrared (MIR) spectral range from 7500 to 400 cm^-1. In this work we extend the spectral range into the near-infrared (NIR) region, demonstrating a method to measure and merge the data sets to create composite n/k data ranging from 10 000 to 400 cm^-1 (1.0 to 25 µm) with absorbance fidelity spanning over four orders of magnitude, and vastly improved signal-to-noise in the NIR. The precision of the composite data is evaluated for three different liquids, focusing primarily on the steps for converting the raw absorbance spectra to k values. The variability in both MIR and NIR data as well as in the final n/k vectors is also investigated for several liquids. For typical liquids, the overall variability (reported as 2σ) in the final n and k-vectors is determined to be ∼0.4% and 3%, respectively. Finally, the derived n/k data are used to calculate absorbance spectra for aerosol droplets, showing marginal variability due to the typical measurement errors in the final n/k vectors.