Applied Spectroscopy最新文献

In-line monitoring of continuous crystallization processes can provide real-time information about the polymorph composition, potentially providing a superior understanding and control of the crystallization kinetics throughout the process. Here, we present a case study using in-line Raman spectroscopy as a process analytical technology (PAT) tool to enable fast, in-situ, non-destructive, and quantitative measurement of complex polymorphic transitions during flow-induced continuous crystallization of a model compound, which has two main polymorphs only showing subtle differences in the fingerprint regions of their Raman spectra. Second derivative Raman spectra were used for qualitative monitoring of polymorph changes, and a Gaussian curve fitting method was developed and utilized for quantitative determinations of polymorph compositions in continuous crystallizations under an array of process conditions. This study illustrates the complex and dynamic nature of polymorph transitions during continuous crystallization under various process conditions as well as the ability of in-line Raman spectroscopy to monitor the process qualitatively and quantitatively in order to have greater understanding of the process design space and to avoid conditions that lead to undesired polymorphs in the crystallization process.

The dynamic spectroscopic method, as a noninvasive blood component measurement method, currently uses spectrometers as the main measurement instrument. However, spectrometers have limited accuracy in measuring light intensity at each wavelength, which restricts the measurement accuracy of the dynamic spectrum method. In this paper, a combination of a multispectral camera and a spectrometer is utilized for the first time to measure spectral photoplethysmography (PPG) signals. Both the high amplitude resolution and high accuracy of the multispectral camera in terms of sampling values and the advantage of the spectrometer in terms of the number of wavelengths are exploited. According to the experimental data, this method effectively improves the measurement results. In particular, when measuring for hemoglobin, the mean absolute percentage error (MAPE) decreased by 25.3% and 22.9%, respectively compared with a single spectrometer and a multispectral camera. For platelet measurements, the MAPE decreased by 28.9% and 22.8%, respectively. For total bilirubin measurements, the MAPE decreased by 14.5 and 26.3%, respectively. It demonstrates that the noninvasive blood component measurement method of a combined multispectral camera and spectrometer can effectively reduce the interference of non-target components and improve measurement accuracy.

Raman microscopes are widely used in various fields and their spectral resolutions differ greatly depending on the system and optical components. Thus, it is important to evaluate the spectral resolution of Raman systems under measurement conditions. Although calcite is a crystal with a trigonal structure and its narrow peak at ∼1086 cm^-1 has been used to evaluate the spectral resolution of Raman spectrometers, the peak width of calcite itself, ∼1.3 cm^-1 at full width half-maximum (FWHM), is not negligible under high spectral resolution conditions. Because the calcite peak at ∼1086 cm^-1 originates from symmetric stretching, which is a common vibration mode for carbonate salts, we examined strontium carbonate (SrCO₃), barium carbonate (BaCO₃), and lead carbonate (PbCO₃) reagents to find a material having a narrower peak width than calcite. SrCO₃, BaCO₃, and PbCO₃ peaks originating from symmetric stretching were observed at 1072, 1059, and 1054 cm^-1, respectively, and their peak widths at FWHM (0.67, 0.92, and 1.09 cm^-1, respectively) were narrower than that of calcite (1.36 cm^-1). The narrow peak width of SrCO₃ was strongly dependent on its purity, probably due to its high structural regularity, and the change in the peak width (FWHM) was only 0.12 cm^-1 between 5 °C and 45 °C. Thus, we concluded that the high-purity SrCO₃ peak at 1072 cm^-1 was the narrowest peak of Raman scattering light under ambient conditions and is suitable for evaluating high spectral resolution for Raman spectrometers.

Fiber-based Raman spectroscopy enhances the Raman signal by maximizing the overlap of the optical field and the gas species. However, filling the hollow-core fiber (HCF) with gas requires time that is dependent on the fiber core diameter, fiber length, and pressure of the gas. At ambient pressure, the fiber gas uptake is driven by diffusion into the fiber ends, severely limiting the response time of the system. By laser drilling access holes to the core along the length of the fiber, the uptake time of the gas is reduced, improving the system response time. In this work, we study the carbon dioxide (CO₂) sensor dynamics based on Raman signal intensity generated in HCFs. The signal intensity versus gas concentration is characterized by controlling the CO₂ concentration in the surrounding environment of the fiber. Next, we characterize the gas uptake time in HCFs as a function of fiber length. Finally, we optimize the access hole configuration along the fiber, demonstrating reduced sensor uptake time by a factor of three.

Polyhydroxybutyrate hydroxyhexanoate (PHBHx) is a bio polymer that is manufactured and degraded by microbes. Because of the potential to replace polymers derived from petrochemicals with these materials, there is a high level of expectation for its commercial uses if its physical and chemical properties can be understood and controlled. Among other things these properties are determined by the polymer's morphology - that is its crystallinity, and orientation of both crystalline and amorphous phases. The focus on the Raman characteristics of the crystalline phase enables elucidation of the characteristics of the polymer experiencing dynamic crystallization under various conditions. In this article we will start by reviewing the changes in the Raman spectrum from an amorphous to a crystalline material in an isothermal crystallization study. In that study a correlation field splitting between a CH stretching band that interacts with the carbonyl group on the opposite chain in the unit cell was identified. Then we will show the polarized Raman spectra of single crystals which enable an explanation of the residual amorphous material seen in the spectra of single crystals. Using the information from the single crystal measurements we can then study the Raman behavior of spherulites and confirm the model that proposes an explanation for the appearance of rings in the polarized light microscope (PLM) images of some spherulites. The polarized Raman studies confirm that the crystal ribbons that grow along the radii are twisting about the growth direction. The 2D-COS analysis of the polarized spectra of spherulites suggest the presence of strain that has been proposed to induce the twisting.

A small remote Raman sensor was used to measure the Raman scattering signal from clear, still water as a function of water depth (12 cm and 396 cm depth), sensor distance above the water surface (20-300 cm), and angle of incidence (0-80°) to the normal of the water surface. Under thick- and thin-sample conditions, the signal depends on either the inverse, or the inverse square, of sensor distance from the water surface, respectively. A model is derived that fits data for different sensor distances, water depths, and angles of incidence. Fits to the measured data are consistent with the known intensity of water Raman scattering and the specifications of the detection system. This manuscript provides a mathematical model that can be used to predict and evaluate the performance of remote sensors and can be expanded to account for differing experimental conditions.

Multivariate regression models were optimized for the quantification of sulfuric acid (H₂SO₄) [0-8 M] and temperature (20 °C-80 °C) in the presence of ammonium sulfate ((NH₄)₂SO₄ [0-0.6 M]) using Raman spectroscopy. Optical vibrational spectroscopy is a useful nondestructive technique for the in situ analysis of complex chemical systems notoriously difficult to monitor in situ and in real-time. Multivariate analysis, a chemometrics method, can be paired with these nondestructive optical methods for determining analyte concentration and speciation in complex solutions, such as dissociated species in polyprotic acids, e.g., H₂SO₄. The effect of temperature is often overlooked although it can have a major influence on speciation and the corresponding Raman spectra. Here, partial least squares regression models were optimized for the quantification of H₂SO₄ and its two deprotonated forms as a function of temperature. Measuring bisulfate as a function of temperature is particularly challenging owing to changes in the second dissociation constant. A designed training set effectively minimized the sample set size and trained a robust predictive model with percent root mean square error of <3% for H₂SO₄. The practical strategy employed here was demonstrated to be effective for building chemometric models that directly account for dynamic temperatures with static samples and is shown to be amenable to flow cell analysis applications with a simple calibration transfer for process monitoring applications.

Non-melanoma skin tumors, mainly basal cell carcinoma and squamous cell carcinoma, are the most common human cancers. Early detection and discrimination of skin tumors is of paramount importance to decision making and treatment. The main treatment for these skin tumors is surgical excision, but its extent is strongly influenced by the preoperative diagnosis. This study presents a new method for skin tumor discrimination based on tumor oxygenation levels extracted from hyperspectral images. Hyperspectral images of 16 skin tumors (four actinic keratoses, six basal cell carcinomas, six squamous cell carcinomas) were obtained prior excision and pathological diagnosis. The concentrations of oxyhemoglobin, deoxyhemoglobin and oxygen saturation levels were measured from hyperspectral images using an algorithm based on the modified Beer-Lambert law. The results were compared with pathology diagnosis. The results revealed that there were statistically significant differences in the mean oxyhemoglobin concentrations and oxygen saturation levels between actinic keratoses and basal cell carcinomas, between basal cell carcinomas and squamous cell carcinomas and between actinic keratoses and squamous cell carcinomas. Deoxyhemoglobin concentrations were not statistically different between the two carcinoma types but were different between carcinomas and actinic keratoses. In conclusion, the proposed method proved that it could be used as a reliable non-invasive diagnostic tool for differentiating benign from malignant skin tumors with the possibility of extending its applications to other medical research areas.

We have begun introducing complex-valued principal component regression (PCR) into spectroscopy. Unlike traditional methods that are constrained to either the real or imaginary axis, this approach allows principal components (PCs) to span the entire complex plane. While this added flexibility enhances modeling capabilities, it also introduces challenges, as existing tools often fail to identify optimal solutions. To address this, we explored two different strategies for computing eigenvectors. The most natural approach is to apply singular value decomposition (SVD) directly to the matrix of complex refractive index spectra. As an alternative, we combined the eigenvectors of the imaginary parts determined by SVD with their Kramers-Kronig transforms, which resulted in 2^N possible superpositions for N PCs. Although the optimal solution may still be unknown, the proposed second method for complex-valued PCR consistently outperformed conventional PCR in the systems investigated. This highlights its potential to enhance data analysis in infrared and Raman spectroscopy.

Understanding the biochemical aging mechanisms of bloodstains is essential for developing reliable forensic methods to estimate the time since deposition (TSD). Although fluorescence spectroscopy is effective for tracking endogenous fluorophores such as tryptophan, nicotinamide adenine dinucleotide (NADH), and flavins, its utility is limited by spectral overlap and sample variability. In this study, we employed two-dimensional correlation spectroscopy (2D-COS) and 2D gradient mapping method to investigate the time-dependent fluorescence changes in bloodstains, gaining molecular-level insights into the aging process. 2D-COS uncovered hidden spectral components and revealed sequential molecular changes, especially in NADH- and flavin-associated bands. The 2D gradient maps further visualized these spectral trends quantitatively over 24 hours of aging. This study focuses on uncovering the biochemical mechanisms underlying bloodstain aging, probed by fluorescence spectroscopy. These findings deepen our fundamental understanding of ex vivo blood degradation and establish a foundation for more accurate and robust forensic applications.