Raman Spectral Characteristics Research Articles

Hyperspectral oblique plane microscopy enables spontaneous, label-free imaging of biological dynamic processes in live animals

Spontaneous Raman imaging has emerged as powerful label-free technique for investigating the molecular composition of medicines and biological specimens. Although Raman imaging can facilitate understanding of complex biological phenomena in vivo, current imaging modalities are limited in speed and sample compatibility. Here, we introduce a single-objective line-scanning light-sheet microscope, named [Formula: see text]-OPM, which records Raman images on a timescale of minutes to seconds. To demonstrate its function, we use [Formula: see text]-OPM to map and identify microplastic particles based on their Raman spectral characteristics. In live zebrafish embryos, we show that [Formula: see text]-OPM can capture wound dynamics at five-minute intervals, revealing rapid changes in cellular and extracellular matrix composition in the wounded region. Finally, we use [Formula: see text]-OPM to synchronize and average 36,800 individual frames to obtain hyperspectral videos of a zebrafish embryo's beating heart at an effective 28 frames per second, recording compositional changes throughout the cardiac cycle.

Temperature Studies of the LaMn2Si2 Intermetallide by the Raman Spectroscopy and Magnetic Force Microscopy Methods

Raman spectra of the LaMn2Si2 compound were obtained for the first time by Raman spectroscopy. The change of Raman spectral characteristics in the temperature range of 263–553 K was investigated. The high sensitivity of the Raman spectroscopy method to a change in the magnetic state caused by a temperature influence has been determined. A change in the spectral characteristics of the vibration mode of manganese atoms near the Curie and Neel temperatures has been revealed. The magnetic force microscopy technique was used to investigate the surface features of the LaMn2Si2 compound at room temperature. A change in the type of magnetic domain structure in LaMn2Si2 after cooling from 298 to 263 K has been found.

Determining the sequence of intersecting lines formed by laser printer toner and seal ink based on confocal Raman spectroscopy.

In the field of questioned document examination, determining the sequence of intersecting lines is still a technical challenge. This study aims to validate whether confocal Raman spectroscopy can determine the sequence of intersecting lines created by laser prints toner and seal ink through empirical research. The study collected 110 varieties of seal ink and 1074 test pages from 66 models of laser printers available in the Chinese market. Based on the Raman spectral characteristics of the seal ink and the microscopic morphology of the toner, 13 types of seal ink and three types of laser printers were selected for further analysis, producing 78 representative samples of intersecting lines. Confocal Raman spectroscopy was applied to the examination of these samples using a point-scanning mode for enhanced accuracy and efficiency. The experimental results demonstrate that confocal Raman spectroscopy can non-destructively and quickly examine the sequence of intersecting lines produced by laser printer toner and seal ink. Variations in toner forms result in differing levels of difficulty in resolving intersection problems, with the sequence of intersecting lines from toner-dense laser printers being the easiest to ascertain. In contrast, those from printers with porous and dispersed toner present a more significant challenge in examination. This study can be corroborated with other methods proposed, and more significantly, it lays the groundwork for addressing intersection problems related to other printing or writing instruments.

Crystallization of Calcium Carbonate and Calcium Phosphate Phases in Silica Hydrogel: Morphological and Compositional Characterization

The present study showcases a series of crystallization experiments using a specially designed double diffusion system to grow crystals belonging to the calcium carbonate–phosphate system. The experimental U-shaped device comprised two vertical solution containers, separated by a horizontal column of silica hydrogel. Each container was filled with 0.5 M CaCl2 and 0.5 M Na2CO3 solutions, which diffused through the gel column over time. Na3PO4 solutions, with 50 and 500 ppm concentrations, were incorporated into the gel in different experiments, resulting in a homogeneous distribution of phosphate concentrations within the diffusion column. After 15- and 30-day incubation periods post-nucleation, the crystals formed in different sections of the gel were carefully extracted and studied with scanning electron microscopy and electron microprobe. Additionally, Raman spectra were collected from the samples using a confocal Raman microscope, providing further insights into their molecular composition and structural properties. The obtained results show that under the induced experimental conditions (i) phosphate incorporates into calcite’s structure, and (ii) the growth of calcium phosphates in the presence of carbonate ions involves the sequential, heterogeneous nucleation of CO3-bearing OCP/HAP-like phases, with Raman spectral characteristics very similar to those of bioapatites.

Quantitative analysis of solid dosage forms of Atenolol by Raman spectroscopy

Objective To develop a Raman spectroscopy-based analytical model for quantification of solid dosage forms of active pharmaceutical ingredient (API) of Atenolol. Significance: For the quantitative analysis of pharmaceutical drugs, Raman Spectroscopy is a reliable and fast detection method. As part of this study, Raman Spectroscopy is explored for the quantitative analysis of different concentrations of Atenolol. Methods Various solid-dosage forms of Atenolol were prepared by mixing API with excipients to form different solid-dosage formulations of Atenolol. Multivariate data analysis techniques, such as Principal Component Analysis (PCA) and Partial least square regression (PLSR) were used for the qualitative and quantitative analysis, respectively. Results As the concentration of the drug increased in formulation, the peak intensities of the distinctive Raman spectral characteristics associated with the API (Atenolol) gradually increased. Raman spectral data sets were classified using PCA due to their distinctive spectral characteristics. Additionally, a prediction model was built using PLSR analysis to assess the quantitative relationship between various API (Atenolol) concentrations and spectral features. With a goodness of fit value of 0.99, the root mean square errors of calibration (RMSEC) and prediction (RMSEP) were determined to be 1.0036 and 2.83 mg, respectively. The API content in the blind/unknown Atenolol formulation was determined as well using the PLSR model. Conclusions Based on these results, Raman spectroscopy may be used to quickly and accurately analyze pharmaceutical samples and for their quantitative determination.

Compositional and structural characterization of dorsal root ganglion neurons and co-cultured Schwann cells by confocal Raman microspectral imaging

Confocal Raman microspectral imaging (CRMI) is a versatile non-invasive technique that allows in vitro cell imaging without any chemical fixation, fluorescent markers or other contrast-enhancing chemicals. In this study, dorsal root ganglion (DRG) neuron and its affiliated Schwann cells (SCs) were co-cultured to unveil their underlying sub-cellular constitutional and structural nature. Both DRG neurons and SCs were derived from neonatal Sprague-Dawley rats and seeded on CaF2 subtracts for spectral analysis. After acquiring Raman hyperspectral datasets, multivariate data analyses, including K-mean cluster analysis (KCA) and principal component analysis (PCA), were successively adopted to study the subcellular structural and compositional information of the measured cells. Univariate spectral analysis was adopted to emphasize the spatial distribution of subcellular constitutions based on the acquired spectral characteristics. Results have shown Raman spectral characteristics of DRG neurons (cell membrane, cytoplasm, organelles, nucleus) and its affiliated SCs (myelin, cell membrane, cytoplasm, nucleus), as well as information on the subcellular distribution pattern of major biochemical components (proteins, cytochrome c, nucleic acids, lipids, carbohydrates). This in vitro spectral-imaging work provides a proof of principle of an analytical method for future studies on the developmental mechanisms of DRG neurons and their molecular bases for the treatment of diseases of the peripheral nervous system.

Comparison of Raman spectral characteristics and quantitative methods between 13CH4 and 12CH4 from 25 to 400 °C and 50 to 400 bar

In recent years, increasing attention has been given to quantifying the isotopic compositions of gases by Raman spectroscopy. However, related research on the carbon isotopes of CH4 is still lacking. In this study, the Raman spectral characteristics of 13CH4 and 12CH4 in the pure CH4 system and in the CH4–H2O system are comprehensively studied at temperatures ranging from 25 to 400 °C and pressures ranging from 50 to 400 bar. For the pure CH4 system, the peak positions of the symmetric stretching band (ν1) of 13CH4 and 12CH4 both shift to a higher wavenumber with increasing temperature and decreasing pressure, and their full width at half maximum (FWHM) values can reach 4.7 cm−1 and 5.5 cm−1, respectively, with increasing temperature and density. The peak position of the ν1 band of 13CH4 is always 4.6–5.1 cm−1 lower than that of 12CH4 under the same conditions, indicating that 13CH4 and 12CH4 can be distinguished by peak position and FWHM in the Raman spectra. Although the calculated Raman shifts (ν0) at zero-density for 13CH4 and 12CH4 are different, the unified equation for determining the density of CH4-rich fluid inclusions is still applicable, as long as to bracket the sample measurement with measurements of reference standards. For the CH4–H2O system, the peak position of the ν1 band of dissolved 13CH4 is approximately 2.5 cm−1 lower than that of 12CH4, while their FWHM values can be more than 12.2 cm−1, causing more difficulty in distinguishing them in aqueous solutions. In addition, Raman quantitative calibration models of 12CH4 and 13CH4 in the CH4–H2O system are established. The difference in the Raman scattering cross section (RSCS) of dissolved 12CH4 and 13CH4, rather than changes in the molar density or RSCS of water is the main reason leading to the difference in the Raman quantitative calibration models of CH4 concentrations between the 12CH4–H2O system and the 13CH4–H2O system. Our work provides a good reference for the in situ identification and quantification of the carbon isotopic composition of CH4 in high-temperature and high-pressure environments.

Serum-based Raman spectroscopic diagnosis of blast-induced brain injury in a rat model.

The diagnosis of blast-induced traumatic brain injury (bTBI) is of paramount importance for early care and clinical therapy. Therefore, the rapid diagnosis of bTBI is vital to the treatment and prognosis in clinic. In this paper, we reported a new strategy for label-free bTBI diagnosis through serum-based Raman spectroscopy. The Raman spectral characteristics of serum in rat were investigated at 3 h, 24 h, 48 h and 72 h after mild and moderate bTBIs. It has been demonstrated that both the position and intensity of Raman characteristic peaks exhibited apparent differences in the range of 800-3000cm-1 compared with control group. It could be inferred that the content, structure and interaction of biomolecules in the serum were changed after blast exposure, which might help to understand the neurological syndromes caused by bTBI. Furthermore, the control group, mild and moderate bTBIs at different times (a total of 9 groups) were automatically classified by combining principal component analysis and four machine learning algorithms (quadratic discriminant analysis, support vector machine, k-nearest neighbor, neural network). The highest classification accuracy, sensitivity and precision were up to 95.4%, 95.9% and 95.7%. It is suggested that this method has great potential for high-sensitive, rapid, and label-free diagnosis of bTBI.

Electrochemical Surface-Enhanced Raman Spectroscopy for Aniline Adsorbed on Silver Electrodes: A DFT Study of the Anharmonic Effects of Amino Wagging Vibrational Modes

Aniline molecules exhibit a special amino wagging vibrational mode on the surface of the silver electrode. The corresponding Raman peak not only displays enhanced Raman signals in surface-enhanced Raman spectroscopy (SERS) experiments but also shows a shift toward higher wavenumbers. This work adopts a molecule-metal cluster model to investigate the normal Raman spectra of aniline molecules and their SERS spectra adsorbed on silver electrode surfaces by density functional theory (DFT) approaches. Based on the harmonic approximation, the influence of anharmonic effects on the normal Raman and SERS spectra of aniline is further considered. Our calculated results of the anharmonic Raman spectra of free aniline molecules show that their anharmonic effect mainly comes from the amino wagging vibrational mode. Then, the anharmonic Raman spectra of aniline binding to neutral and positively charged silver clusters were calculated and compared with the harmonic Raman spectra. It was found that the coupling effect between vibrational modes also greatly affects the Raman spectral characteristics. Finally, the excited state energy gap and pre-resonance Raman spectra of the aniline–silver cluster complexes are studied, and it is believed that there may be a charge-transfer enhancement mechanism.

Deciphering the Color Origin of Pink Conch Pearl Using Nondestructive Spectroscopies and DFT Calculations

Conch pearl is a calcareous concretion produced by the Queen conch mollusk and is of extremely high economic value. Its attractive pink color has remained a mystery for hundreds of years. This difficulty limits the development of cultivation and preservation technology of conch pearl. Due to its super-high value, it is generally impossible to use destructive chemical analysis methods. Here, various nondestructive spectroscopic analysis methods and theoretical calculations were used to reveal the color origin of pink conch pearl. The experimental Raman and UV-Vis spectroscopies were used to characterize the color and pigments. We further discuss the pigments in conch pearl by comparing the Raman spectral characteristics and pigments of the red coral. Based on the characteristics of the experimental spectra, we speculate that the carotenoids color the conch pearl. The theoretical Raman and UV-Vis spectra of all-trans polyene and carotenoids were simulated using DFT calculations. According to the results, we proposed that the pigments in pink conch pearl are polyenes containing 11 shortened C–C bonds with multiplicities > 1.5, which may be demethylated carotenoids.

Recognition of Nucleophosmin Mutant Gene Expression of Leukemia Cells Using Raman Spectroscopy

As a label-free, nondestructive, and in situ detection method, Raman spectroscopy analysis of single cells has potential application value in biomedical fields such as cancer diagnosis. In this study, the Raman spectral characteristics of nucleophosmin (NPM1)-mutant acute myeloid leukemia (AML) cells and nonmutated AML cells were investigated, and the reasons for the differences in spectral peaks were explained in combination with transcriptomic analysis. Raman spectra of two AML cell lines without NPM1 mutation (THP-1 and HL-60) and the OCI-AML3 cell line carrying the NPM1 mutant gene were cultured and collected experimentally. It was found that the average Raman spectra of NPM1 mutant and nonmutated cells had intensity differences in multiple peaks corresponding to chondroitin sulfate (CS), nucleic acid, protein, and other molecules. The differentially expressed genes were identified by quantitative analysis of the gene expression matrix of the two types of cells, and their roles in the regulation of CS proteoglycan and protein synthesis were analyzed. The results showed that the differences between the two types of cells expressed by the single-cell Raman spectral information were consistent with the differences in transcriptional profiles. This research could advance the application of Raman spectroscopy in cancer cell typing.

Raman spectral characteristics of 12CO2/13CO2 and quantitative measurements of carbon isotopic compositions from 50 to 450 °C and 50 to 400 bar

The carbon isotopic composition of CO2 is traced to its different origins and widely used in the fields of geology, biology, and chemistry. Raman spectroscopy can be performed in situ, is nondestructive, and requires no sample preparation; these characteristics enable Raman spectroscopy to be considered a new alternative method to measure the carbon isotopic composition of CO2. In this work, Raman spectra of high-purity 13CO2, 12CO2, and six 12CO2-13CO2 binary mixtures with known mixing ratios were collected using a High Pressure Optical Cell (HPOC) at 50–450 °C and 50–400 bar. The results showed that the characteristic peak positions of both 13CO2 and 12CO2 shift to lower wavenumbers with increasing temperature and decreasing pressure, but the peak positions of 13CO2 show a larger shift. The peak position difference of the corresponding characteristic peaks between 13CO2 and 12CO2 is greater than 15 cm−1 under the above temperatures and pressures, and the peaks can be distinguished. However, ν−13 overlays νH.B.12 near 1265 cm−1, ν+12 overlaps νH.B.13 near 1288 cm−1. The existence of 13CO2 can cause a change in the Fermi diad splitting of 12CO2 and affect the establishment of CO2 Raman densimeters. The positive correlation obtained between the peak intensity ratio and the content ratio is affected by temperature, pressure, and 13CO2 content. I+13/I+12 and I−13/I−12 were selected as the quantitative indices to establish Raman quantitative analysis models for the determination of the carbon isotopic composition of CO2, which can be applied to in-situ measurements of high-temperature and high-pressure systems.

Biomarker Based Detection and Staging of Breast Cancer from Blood Using Raman Spectroscopy and Deep Learning Technique

Breast cancer (BC) or breast neoplasm is causing major menace to the life of women around the world. The significance of early detection and staging of BC has been substantial in diagnosing protocol. This work aims to develop an automated system that combines multivariate data analysis (PCA - principal components analysis) with ensemble recurrent neural network models (stacked OGRU-LSTM) to identify Raman spectral characteristics that can be used as spectral cancer markers for the detection of BC progression and staging. Features of blood plasma from histopathologically diagnosed BC candidates were compared to healthy ones in this study. The same is performed on different leading classification models as the stacked basic RNN, the stacked-RNN-LSTM, and RNN-GRU models. A total of 2,340 Raman spectra generated is evaluated in this study. It is found from the study that stage 3 and stage 2 are structurally identical, but with PCA-Factorial Discriminant Analysis (FDA) they can be distinguished from each other, hence the Raman spectrum pertaining to blood plasma samples of the BC candidates is classified efficiently, yielding potentially high values of specificity and sensitivity for all the BC stages. Comparative classification results show that the stacked OGRU-LSTM model outperforms well for BC detection, and better differentiates various stages of BC by employing the multivariate data analysis technique. The stacked OGRU-LSTM model achieved the highest classification accuracy (97.89 %), Cohen-kappa score (0.928), F1-score (0.957), and the lowermost number of test loss and MSE (0.037), indicating that the model outperforms other baseline classifiers. HIGHLIGHTS The use of Raman spectroscopy in conjunction with deep learning models and multivariate data analysis to diagnose and categorize blood plasma samples as cancerous or noncancerous and staging of breast cancer based on their chemical composition To address the issue of underfitting and overfitting caused by insufficient Raman spectral data, spectral data augmentation techniques were implemented The potential for this technique is used to accurately classify breast cancerous samples and hence reduce the number of unnecessary excisional breast biopsies Stage 3 and stage 2 of breast cancer were found to be structurally identical but can be distinguished from each other using PCA-Factorial Discriminant Analysis with high specificity and sensitivity for all BC stages The stacked OGRU-LSTM model outperformed other baseline classifiers for breast cancer detection and better differentiated various stages of breast cancer by employing multivariate data analysis technique GRAPHICAL ABSTRACT

A Study on the Raman Spectral Characteristics of Garnet from the Jiama Copper Polymetallic Deposit in Tibet

Raman spectroscopy is an important method to analyze and measure mineral composition and structure, which has the advantages of being non-destructive and rapid. This study considered garnet from the Jiama copper polymetallic deposit in Tibet to carry out micro-Raman spectrum and electron microprobe research to analyze the Raman spectrum characteristics of garnet with different components to reveal its indicative significance for garnet composition and skarn mineralization. The results showed that the Raman peaks T, X, A1, A2, and A3 shift toward lower wavenumber with the increase in andradite (And) content. The variations in T, X, and A2 are more obvious than those of A1 and A3. When And > 50%, the three Raman peaks (T, X, and A2) range are 173–174, 234–239, 513–525 cm−1; when And < 50%, they are 177–178, 240–244, 527–543 cm−1. The Raman peaks also shift with the cation radius and relative atomic mass. Different peaks moved in the low-frequency direction with the increase in the X2+ and Y3+ radius, and the X2+ atomic mass. The Raman spectrum can indicate the composition change in garnet. Raman spectrum analysis of garnet is of great significance for skarn zoning and prospecting.

Evolution of Raman and photoluminescence spectral characteristics of monolayer CVD-MoS2 over a wide temperature range

In this study, the temperature-dependent characteristics of monolayer MoS2 flakes produced by chemical vapor deposition (CVD) are examined at temperatures ranging from 83 to 483 K. The effect of temperature change on chemical vapor deposited MoS2 flakes transferred from glass to Si/SiO2 substrates using a modified PMMA assisted method, is also investigated using µ-Raman and photoluminescence spectroscopy. Our results show that the thermal coefficient of the A1 g Raman mode, which is inversely proportional to thermal conductivity, decreases from − 0.01275 to – 0.01352 cm−1 K−1 after the transfer process. The photoluminescence (PL) spectral intensity of both samples (i.e., as-grown on glass substrates and transferred on 300 nm Si/SiO2) is observed to fall with an increase in temperature and the bandgap decreased from 1.90 eV to 1.86 eV for the as-grown sample and from 1.85 to 1.81 eV for the transferred sample. The PL and Raman spectral analysis results show that the vibrational and excitonic properties of 2D MoS2 flakes are not substantially affected by transfer from one substrate to another. Monolayer MoS2 samples are also observed to be unaffected by temperatures as high as 583 K.

Raman Spectroscopy Studies of Equilibrated Ordinary Chondrites with H and L Group and Shock Metamorphism Degrees

Ordinary chondrites are the most common type of chondrites. As a non-destructive, rapid, and semi-quantitative technology, Raman spectroscopy is widely used in geoscience. This paper presents the results of a Raman spectroscopic study that we conducted for 16 ordinary chondrites with different chemical groups and variable degrees of shock metamorphism. We found that: (1) the relationship between the Fe composition of olivine and pyroxene and the characteristic peaks of the Raman spectrum established by predecessors cannot be refined to the range of meteorites, the shock on meteorites also affects the Raman spectral characteristics of minerals and (2) the full width at half maximum (FWHM) of the shocked minerals (including high-pressure minerals) in meteorites increases in the Raman spectrum, however, no clear numerical relationship with pressure was found. Based on these data, we assess that the feasibility of Raman spectroscopy for the classification of chemical group and shock metamorphism in ordinary chondrites is not well established.

Study on the Raman spectral characteristics of dynamic and static blood and its application in species identification.

This paper proposes a method to identify the blood of 4 poultry species (chicken, duck, goose and pigeon) based on Raman spectroscopy and its baseline. Samples were prepared by pretreatment methods of freezing, thawing, and dilution. The Raman spectra of dynamic blood and static blood were measured, respectively, and the spectral differences between the two research schemes were analyzed. The four species of poultry blood were identified based on the Raman spectroscopy and its baseline. The results show that the method can realize the identification of four species of poultry blood. In addition, the potential of Raman spectroscopy as a technique for determining carotenoids in blood has been clearly confirmed, which opens up the possibility to quickly determine whether poultry eats feed containing carotenoids without sample preparation.

Origin and accumulation mechanisms of deep paleozoic oil and gas: A case study of the central Tarim basin, western China

Old strata and deep petroleum systems are becoming increasingly important. The Cambrian-Lower Ordovician petroleum reservoirs in the eastern Tazhong Uplift, central Tarim Basin, western China were studied comprehensively using various methods, including biomarkers, carbon isotopes of oil and gas, TOC and Rock-Eval pyrolysis of potential source rocks, as well as fluid inclusions, thin sections of dolomite rocks and Raman spectra of reservoir bitumen. The results show that the content of C 28 steranes among the C 27-29 steranes in most of the oil samples is greater than 0.25. The original hydrocarbon generation and expulsion potential of Cambrian and Lower Ordovician shale samples from the nearby Manjiaer Depression is considerable, and the oils are considered mainly derived from the Paleozoic shales in the Manjiaer Depression and the surrounding slops. Three notable types of oil and gas reservoirs were recognized in the Cambrian and Ordovician dolomite rocks: 1) the relatively well preserved primary reservoirs; 2) the residual reservoirs after deep oil-gas cracking with participation of thermochemical sulfate reduction (TSR); 3) the reformed reservoirs by the late charged high mature gas. In the vicinity of the No.1 fault zone, the effect of late gas charging and invasion is remarkable. They are mostly the mixture of gas cracked from both crude oil and heavy hydrocarbon gas in high mature stage. Oil and gas-liquid inclusions detected in the Cambrian reservoirs together with the Raman spectral characteristics of reservoir bitumen confirm the existed Cambrian paleo-oil reservoirs and oil cracking process. The gypsum-salt rock developed in Cambrian system is considered as a crucial factor for the primary oil and gas reservoirs, and the nearby areas within or below the strata where these gypsum-salt rock developed are suggested as favorable targets for deep to ultra-deep petroleum exploration. • Geochemistry characteristics of Cambrian and lower Ordovician oils were revealed. • Three modes of petroleum reservoirs in terms of formation mechanisms were proposed. • Major charging periods based on the fluid inclusions and burial-thermal history was suggested. • Hydrocarbon generation potential of Cambrian shale and Ordovician argillaceous dolomite was evaluated. • The sources and genesis of Cambrian and lower Ordovician oil and gas were clarified.

Carbonate assemblages in Cold Bokkeveld CM chondrite reveal complex parent body evolution

AbstractThe paragenesis of carbonates in the Cold Bokkeveld CM chondrite is determined from a detailed petrographic, chemical, spectroscopic, and isotopic study of nine associations of carbonates (aragonite, calcite, and dolomite) with other secondary minerals that occur within the meteorite. Our study reveals the existence of carbonates displaying petrographic features that are distinct from those of type 1 and type 2 carbonates commonly observed in CM2 meteorites. These include carbonates interstitial to octahedral magnetite crystals, for which a new designation of “type 1c” is suggested. The O isotopic values of dolomite (δ18O ranging from +21.1 to +25.8‰ and Δ17O from −4.9 to −4.0‰) are similar to those measured in dolomites from other CM chondrites. The presence of complex carbonates with a CaCO3 core and Mg‐enriched rim implies several generations of fluids and/or their evolving composition on the CM parent body(ies). Petrographic characteristics indicate at least six stages of potentially overlapping carbonate and phyllosilicate formation events. We show that type 1 and type 2 calcite have distinct Raman spectral characteristics. Type 1 calcite is characterized by very broad peaks, whereas type 2 calcite displays narrow peaks similar to those of typical abiotic terrestrial calcite, suggesting high crystallinity. A carbonate Raman spectrum showing features characteristic of both aragonite and calcite likely documents an aragonite‐calcite phase transition. Raman spectroscopy also reveals the presence of organic matter in the majority of carbonates. This indicates that organic carbon was mobilized by aqueous fluids for extended periods.

Quantitative Detection of Acid Value During Edible Oil Storage by Raman Spectroscopy: Comparison of the Optimization Effects of BOSS and VCPA Algorithms on the Characteristic Raman Spectra of Edible Oils

Acid value is one of the crucial indicators reflecting the quality of edible oil during storage. This study proposed a quantitative detection method for edible oil acid value during storage based on reduced Raman spectral characteristics. First, the Raman spectra of edible oil samples from different storage periods were collected, and the original spectra were preprocessed using Savitzky-Golay smoothing (SG smoothing), multiple scattering correction (MSC), adaptive iteratively reweighted penalized least squares (airPLS) combined with normalization. Then, bootstrap soft shrinkage (BOSS) and variable combination population analysis (VCPA) methods based on model population analysis (MPA) strategy were introduced to optimize Raman spectral characteristics. Finally, the SVM prediction model based on the optimized characteristic Raman shifts was established to realize the quantitative detection of edible oil acid value during storage. The results showed that compared with the full-spectrum SVM model, the BOSS-SVM and VCPA-SVM models had no overfitting during the training process, and the VCPA-SVM model obtained the best generalization performance, and its $$ {R}_{\mathrm{P}}^2 $$ and RMSEP in the prediction set were 0.932 and 0.153, respectively. This study sufficiently demonstrated that the SVM model integrated with the characteristic Raman shifts which were optimized by the BOSS and VCPA was a promising tool to monitoring the acid value in edible oil during the storage, and the characteristic Raman shifts of Raman spectra optimized by the VCPA was of more interpretation and pertinence.