Applied Spectroscopy最新文献

Analyzing the composition of animal hair fibers in textiles is crucial for ensuring the quality of yarns and fabrics made from animal hair. Among others, Fourier transform infrared (FT-IR) spectroscopy is a technique that identifies vibrations associated with chemical bonds, including those found in amino acid groups. Cashmere, mohair, yak, camel, alpaca, vicuña, llama, and sheep hair fibers were analyzed via attenuated total reflection FT-IR (ATR FT-IR) spectroscopy and scanning electron microscopy techniques aiming at the discrimination among them to identify possible commercial frauds. ATR FT-IR, being a novel approach, was coupled with chemometric tools (partial least squares discriminant analysis, PLS-DA), building classification/prediction models, which were cross-validated. PLS-DA models provided an excellent differentiation among animal hair of both camelids and eight animal species. In addition, the combination of ATR FT-IR and PLS-DA was used to discriminate the cashmere hair from different origins (Afghanistan, Australia, China, Iran, and Mongolia). The model showed very good discrimination ability (accuracy 87%), with variance expression of 94.88% and mean squared error of cross-validation of 0.1525.

A compact dual-gas sensor based on the two near-infrared distributed feedback diode lasers and a multipass cell has been established for the simultaneous measurement of methane (CH₄) and acetylene (C₂H₂). The time division multiplexing calibration-free direct absorption spectroscopy is used to eliminate the cross interference in the application of multicomponent gas sensors. A wavelength stabilization technique based on the proportion integration differentiation feedback control is developed to suppress laser wavelength drift and an H-infinity (H_∞) filter algorithm to reduce the system noise. The results show that the detection sensitivity of CH₄ and C₂H₂ reaches 39.9 parts per billion (ppb) and 47.3 ppb in the optimal integration time of 556 s and 312 s, respectively. In addition, the 31 consecutive hours measured results of CH₄ in outdoor ambient air show that the proposed detection technology is very suitable for high-precision in-situ measurement of trace gases.

Two-dimensional correlation spectroscopy (2D-COS) is a highly sensitive technique for detecting deviations from the Beer-Lambert approximation through asynchronous spectra. In this study, we apply 2D-COS to examine such deviations in the context of this approximation. While conventional molecular IR spectroscopy literature suggests a linear correlation between absorbance, molar concentration, and sample thickness, a more rigorous analysis, supported by electromagnetic theory, demonstrates that this assumption does not hold, even under ideal conditions. As a result, disproportionate spectral changes, caused by interference effects, give rise to distinct patterns in asynchronous 2D-COS IR spectra. To illustrate this, we investigate the thickness dependence of absorbance in poly(methyl methacrylate) (PMMA) layers deposited on calcium fluoride (CaF₂) and Si. Our findings reveal systematic variations not only in absorbance values but also in band shapes and peak positions. 2D-COS emerges as a powerful tool for identifying and analyzing these patterns.

The single parameter detection of temperature (H₂O) is no longer sufficient for the absorption combustion diagnosis. There is a huge demand for simultaneous computed tomography (CT) diagnosis of multi-parameters. This paper studied CO and NO, two representative combustion products based on tunable diode laser absorption spectroscopy (TDLAS) and ultraviolet absorption spectroscopy (UVAS). Different from the research on low detection limits, the absorbance needs to be corrected in high-temperature and high-pressure conditions due to the equipment performance of the CT system. A high-temperature and high-pressure chamber system was applied for the basic absorbance experiment. The corrected absorbance databases of 2325.2/2326.8  nm for CO, and 215/226  nm band for NO were established. The corrected absorbance databases were first compared with the HITRAN and ExoMol databases. The accuracy of the corrected databases was also analyzed by standard gas with 1D detection in the high-temperature and high-pressure chamber and two-dimensional (2D) reconstruction in a customed CT cell. The maximum CO mean relative error (MRE) of the 2D results is 2.75% while the maximum NO MRE is 4.99%. This study provides a basis for research on the CO and NO distribution in high-temperature and high-pressure combustion fields.

Significant dehydration can increase thermoregulatory and cardiovascular strain and impair physical and cognitive performance. Despite these negative effects, there are currently no objective, non-invasive tools to monitor systemic hydration. Raman spectroscopy is an optical modality with the potential to fill this gap because it is sensitive to water, provides results quickly, and can be applied non-invasively. In this work, high wavenumber Raman spectroscopy has been developed toward detection of systemic hydration via validation with tissue-mimicking phantoms, followed by three in vivo feasibility studies to investigate the relationship between spectral features and systemic hydration. The area under the curve (AUC) of the water bands and the ratio of water bands to CH bands are Raman-derived metrics that can be used to describe systemic hydration. Here, we determined a trend in decreasing water bands AUC after exercise, although the magnitude of the change was highly variable. In investigating the sources of variability, we identified significant inter-subject variability and a failure of current clinical standards to benchmark our developed technique against. Despite the high variability, we found that multiple anatomical locations were suitable for collecting the spectral measurements. While the high degree of variability may confound the use of Raman spectroscopy for non-invasive hydration monitoring, when implementing additional study standardization, significant differences (p <.05) in spectral metrics can be identified before and after exercise. Raman spectroscopy can allow for rapid, non-invasive detection of systemic hydration, which would improve routine hydration monitoring and reduce the incidence of negative side effects associated with dehydration.

We evaluated the application of Fourier transform infrared (FT-IR) microspectroscopy in the mid-IR region (1500-550 cm^-1) in reflectance mode as a semi-automated tool to quantify common heavy minerals (HM) found in natural sediments and sedimentary rocks. An in-house database of IR spectra for the main HM was acquired. Then, automated HM identification using FT-IR spectroscopy was tested on synthetic mixtures with known HM proportions. HM fractionation during sampling and mounting in epoxy is evaluated by testing several sample preparations techniques. Overall, HM are properly determined using FT-IR microspectroscopy. Most of the HM are found in proportions comparable to those documented in the synthetic mixtures. Main drawbacks to this method include: (i) the mid-IR region does not give access to the absorption bands of some HM, such as fluorite, pyrite, and cassiterite, compared to other methods such as Raman microspectroscopy, (ii) the failure to discriminate titanium dioxide (TiO₂) polymorphs, and (iii) large spectral variations in some mineral groups such as amphiboles. Beyond these limitations, mid-FT-IR microspectroscopy in reflectance mode can be used to accurately determine HM proportions and could be simpler, faster, and/or cheaper when compared to other methods such as optical microscopy or scanning electron microscopy.

Micro-Raman spectroscopic analysis of a fossil sample of Vicarya callosa japonica was performed to investigate the chemical process of fossilization. The Vicarya sample, originating from the Miocene Katsuta Group, Okayama prefecture, southwestern Japan, had a conical shell body with multiple protuberances on the outer layer. The interior of the shell was filled with a carbonate sediment. Raman mapping combined with principal component analysis (PCA) and partial least squares regression (PLSR) analysis were performed on the sample. Well-preserved, in vivo aragonite was found to be distributed on the shell and near the boundary between the internal carbonate precipitates and the shell. The internal precipitates were composed of pure calcite and black carbonates. The black-colored precipitates contained pyrite, suggesting that the carbonates were derived from the same biogenic tissue as the carbonate concretions and were the starting point for their crystallization. The rapid formation of the precipitates, also similar to that of carbonate concretions, and the suppression of the demineralization effect of the shell from pore water in the sediment may have contributed to the preservation of the aragonite. The reaction of the transition from aragonite to calcite in the shell progressed to some extent and crystallization was completed before the transition to calcite was complete.

When injection-molded polyoxymethylene is heat-treated below its melting point, it shows increased polarized reflection along the injection direction, as confirmed through micro-infrared spectroscopy. A characteristic dip or step-like structure appears around 940 cm^-1. Previously, the origin of this structure was unclear. However, we have found that it can be explained by refining the calculation model to account for the relative permittivity perpendicular to the sample surface.

This study presents an optical sensor system utilizing multi-reflectance spectroscopy (MRS), specifically designed for in-line applications to enable the real-time determination of fat and protein content in milk products, simultaneously. This method employs multiple light wavelengths and various illumination-detection geometries. A field study was conducted in a milk mixing plant, where measurements were obtained from milk products with varying fat and protein concentrations, with a particular focus on recombined milk samples and a brief comparison to conventional milk products. In a first step the experimental data are compared with simulation data obtained from an analytical MRS formula. The fundamental spectroscopic characteristics, particularly the dependence of reflectance values on fat concentrations, as well as the relationship between wavelength and reflectance, remained consistent. However, some experimental bias was observed in the absolute values when comparing the analytical and experimental results. Secondly, to get reflectance models multi-linear regressions (MLR) were carried out based on the experimental and analytical data as well fat and protein content obtained from traditional wet chemical methods. To estimate the model accuracy the root mean square error (RMSE) has been used yielding around 0.1 wt% for fat and protein. A validation procedure using recombined milk results in approximately 0.1 wt% for fat and around 0.2 wt% for protein. Finally, it is shown that the process sample temperature has only a small influence on the reflectance. In contrast the homogenization pressure significantly influences the reflectance and should be considered to ensure accurate monitoring.