Applied Spectroscopy最新文献

This study proposes a method to remove background pixels from near-infrared hyperspectral images based on the pixel-wise standard deviation of reflectance method (px-wise SD method). This method calculates the standard deviation (SD) of reflectance in each pixel, namely each spectrum, and determines a threshold to distinguish between background and object pixels from the resulting histogram of the px-wise SD. The method effectiveness is evaluated using hyperspectral images of a leaf-like pastry with a hole placed on either a low-reflectance sheet or white paper. On white paper, the px-wise SD of reflectance exhibits a trimodal histogram with two prominent peaks and one small peak between them. The prominent peak with a lower SD corresponds to the white paper pixels, whereas the other peak with a higher SD is associated with the surface and edge pixels of the pastry. The small peak represents the pixels of the hole. The background and object pixels can be effectively separated by setting a threshold between this small peak and the prominent peak for the pastry pixels. Moreover, the mean spectrum calculated using only object pixels remains consistent, regardless of the type of background material. Conversely, the mean spectrum calculated using all pixels is distorted due to the spectral inclusion of the background material.

Some attenuated total reflection (ATR) correction formalisms share the drawback that they can only be applied to materials with relatively low oscillator strength, as they rely on one or another form of the low absorption assumption. In this contribution, we present an iterative formalism that does not suffer from this limitation and can be applied not only to attenuated total reflection spectra but also to spectra acquired under internal reflection conditions at subcritical incidence angles. Its accuracy is primarily limited near the critical angle and Brewster's angle. The formalism is based on the perpendicular component of the wavevector and Fresnel's equations, and it is fully compatible with wave optics. Its application is straightforward, and a corresponding program is available via the Supplemental Material.

We describe a radioisotope-excited energy dispersive X-ray fluorescence spectrometric facility for the elemental analysis of minerals containing the rare earth elements (REEs) by the use of the K-line X-rays. Two ²⁴¹Am sources are used in purpose-designed holders that fit a high-resolution solid-state germanium detector. The system is capable of exciting all the light actinides up to element 69, Tm. The analysis through the well-separated K-lines allows an easy identification of lanthanide elements with advantages over traditional L-line detection particularly in mineral samples with high Fe concentration, enabling the recognition of most lanthanide elements at values close to 10 ppm. We report the achieved elemental sensitivity obtained with a set of pure element standards and spectra of mineral concentrates derived from a REEcontaining Venezuelan Laterite.

Sensing with undetected photons has enabled new, unconventional approaches to Fourier transform infrared spectroscopy (FT-IR). Leveraging properties of non-degenerate entangled photon pairs, mid-infrared (mid-IR) information can be accessed in the near-infrared (near-IR) spectral domain to perform mid-IR spectroscopy with silicon-based detection schemes. Here, we address practical aspects of vibrational spectroscopy with undetected photons using a quantum FT-IR (QFT-IR) implementation. The system operates in the spectral range from around 3000 cm^-1 to 2380 cm^-1 (detection at around 12 500 cm^-1) and possesses only 68 pW of mid-IR probing power for spectroscopic measurements with a power-dependence of the signal-to-noise ratio of 1.5 × 10⁵ mW^-1/2. We evaluate the system's short- and long-term stability and experimentally compare it to a commercial FT-IR instrument using Allan-Werle plots to benchmark our QFT-IR implementation's overall performance and stability. In addition, comparative qualitative spectroscopic measurements of polymer thin films are performed using the QFT-IR spectrometer and a commercial FT-IR with identical resolution and integration times. Our results show under which conditions QFT-IR can practically be competitive or potentially outperform conventional FT-IR technology.

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.