Applied Spectroscopy最新文献

Presented is a perspective proposing to expand some fragmented spectroscopic modeling and data analysis practices by incorporating multivariate ideologies. For example, through recognizing the theory of analytic chemistry (TAC) by Booksh and Kowalski, it is common to use the multivariate processes (higher orders) of multiple wavelengths for regression and prediction or classification, fusing multiple instruments, or applying multi-way methods such as parallel factor analysis (PARAFAC). Each wavelength, instrument, PARAFAC order deliver different views of underlying sample-wise full matrix effects adding more information per dimension for improved data characterizations. Reasoned here is that model selection, figures of merit, and sample similarity assessments for model prediction reliability, outlier detection, or classification purposes can meaningfully progress by recognizing the multivariate principles of the TAC and additionally, the importance of the Rashomon effect. Applying the Rashomon effect with the TAC removes conventional fragmented data analysis approaches bringing a more wholeness to data analysis. Included in this discussion is that due to the Rashomon effect, interpretation of spectral models is not reasonable. For an uncommon view of these concepts, the perspective ends with drawing parallels between sample-wise matrix effects and the concepts explicate and implicate orders from physicist David Bohm's depiction of our physical and conscious world and universe. It is hoped that this perspective tempts reflection in your particular area of spectroscopy.

Due to the growing interest in high-purity bioplastics for emerging applications, we investigated the solution crystallization of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHx) from a chloroform solution using advanced spectroscopic techniques. Compared to melt crystallization, solution crystallization proved to be a more complex process. Solvent evaporation led to the formation of amorphous PHBHx and less-ordered crystallites. Subsequently, a distinct intermediate species of slightly disordered crystals formed, eventually transforming into more ordered crystalline structures. To analyze the time-dependent attenuated total reflection infrared (ATR-IR) spectra during crystallization, we employed two-dimensional correlation spectroscopy (2D-COS) and codistribution spectroscopy (2D-CDS). To streamline the 2D analysis of this complex dynamic system, we utilized a correlation filter (CF) technique to attenuate interfering contributions from overlapping peaks.

This comprehensive survey review offers the trajectory of research dissemination in the field of two-dimensional correlation spectroscopy (2D-COS) from 1 July 2022 to 17 June 2024. It covers books, reviews, tutorials, innovative concepts and theories, patents applications, and diverse applications that emerged during this period, as well as instances of improper usage or citations of 2D-COS. Innovations in probe integration, data analysis, and technical methodologies highlight the expanding role of 2D-COS in materials science, environmental monitoring, and biological system. This review shows the dynamic growth and diversification of 2D-COS across in many scientific fields.

In attenuated total reflection (ATR) spectroscopy, the presence of an evanescent field penetrating the sample is generally considered crucial. However, according to wave optics, this evanescent field vanishes when the rarer medium is absorbing, and the attenuation of total reflection results from transmission into this medium. While the evanescent field may not play a significant role in this scenario, a closer examination of the relevant relationships reveals that the system's properties vary smoothly with both the angle of incidence and the imaginary part of the dielectric function. This effect can be further illustrated by comparing electric field maps and spectra for semi-infinite rarer media with those for rarer media composed of layers with thicknesses on the order of the wavelength. In the latter case, ATR spectra can be recorded well below the critical angle, where no evanescent field exists. If the layer is vacuum and the underlying semi-infinite medium is assumed to have the same refractive index but is weakly absorbing, tunneling and frustrated total reflection can be observed. Reflecting on our results, we can now define the critical angle in the presence of absorption as the point at which the real and imaginary parts of the perpendicular component of the wavevector become equal. Overall, we conclude that evanescent waves play little to no significant role. Any deviation from total reflection can be attributed to transmission through the ATR crystal-medium interface.

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.