Journal of Raman Spectroscopy最新文献

The Maillard reaction is a reaction between sugar and the amino group of proteins. Herein, N_α-acetyl lysine (Ac-Lys) and fructose were the model compounds. Structural information of the intermediates and products of the reaction at pH 7.4 and 37°C was obtained using UV–Vis absorption, fluorescence, and 785-nm excited non-resonance Raman spectroscopy. In the 6-h reaction, three independent components in the spectroscopic data were attributed to the solvated reactants (A), their complex (B), and a covalent-bonded product (C). The rate constant of the change in the fraction from A to B and B to C were (9.9 ± 0.1) × 10⁻³ and (3.3 ± 0.1) × 10⁻³ min⁻¹, respectively. Polymeric Maillard reaction products were not yet formed. The structures of the solute molecules in each state were discussed based on the spectroscopic data.

The application of Raman spectroscopy in the meat processing industry as a quality assurance is dependent on its ability to differentiate tissues from the animal. Meat is commercialised as different cuts with variations in quality and financial value. Whilst it is possible to conduct some analysis on meat quality, there are high costs and time involved. The meat processing industry could benefit from rapid methods for characterising meat quality for large quantities. This study demonstrates the ability of combining Raman spectroscopy with chemometrics to discriminate tissues in a chicken carcass. All spectra from the different tissues were analysed by applying chemometrics. The principal component analysis (PCA) and discriminant function analysis (DFA) showed successful classification of different muscles and tissues.

The quality and the security of preparations in hospital centres are essential to guarantee the patient's safety. The development of fast and efficient analytical methods is required to control the finished product before use. In this context, the study aimed to compare the performance and interchangeability of two spectral analytical methods: the flow injection analysis (FIA) with UV detection and the Raman spectroscopy for the quality control of preparation before use to quantify the remdesivir as a SARS-CoV-2 drug. A quantitative study of remdesivir was performed using clinically relevant concentration solutions ranging from 0.25 to 1.625 mg.mL⁻¹ in 0.9% NaCl. Samples were analysed by FIA-UV at 245 nm and by a handheld Raman spectroscopy at 785 nm. Quantitative models were developed using a calibration set (n = 45 samples) and optimized using a validation set (n = 27). An external validation test set (n = 58) was used to compare the two methods by a Bland–Altman plot. Partial least square regression was used to analyse Raman spectra, while univariate analysis was performed at 245 nm for FIA-UV. The regression coefficient was higher than 0.990 for both methods, and the root mean square error of prediction was 0.031 mg.mL⁻¹ for Raman spectroscopy. The Bland–Altman plot confirmed the interchangeability of the two methods and the potential of Raman spectroscopy to control remdesivir during clinical preparation in the hospital.

Nitrogen-based compounds are widespread in the environment due to various sources of natural and anthropogenic origin that introduce them from the most reducing form (the acidic ammonium cation) to the most oxidized (the nitrate anion). In addition, some environmental conditions, such as pH and redox potential, favor secondary reactions of nitrogenous compounds. An example of this is the harmful effect of nitrates on cultural heritage (CH), which poses a threat to its preservation. This is due to their high solubility and mobility, which allow them to penetrate the structure of the materials. As a result of their crystallization/dissolution and hydration/dehydration cycles, the precipitation of nitrate salts in the pores causes internal fractures, leading to the subsequent deterioration and loss of the material. The detection of these salts is a straightforward process in analytical chemistry, but it is imperative to use nondestructive and noninvasive analytical techniques, such as Raman spectroscopy, because of the need to preserve CH. In this work, we have compiled the sources and pathways that contribute to the formation of nitrogen-based compounds, especially nitrate salts in various CH components. Finally, the Raman spectrum characteristic of the nitrate family has also been explained, including the most damaging nitrates found in CH, such as niter, nitratine, nitrocalcite, nitromagnesite, nitrobarite, and nitrammite, and has been compiled. In addition, less common nitrates, some nitrites, and other ammonium compounds have been included in this database.

In this study, an antiretroviral drug emtricitabine (also known as FTC or Emtriva) was detected and quantified down to 40 ng/ml by using surface-enhanced Raman spectroscopy (SERS). Its aqueous standards were tested with two types of silver nanoparticles (colloidal and dendritic) using a specially developed aluminum well plate. The SERS spectra were acquired using a Raman scanning device with 30-μm spatial resolution. The spectral data were analyzed using a new approach for the discrimination of the spatially acquired spectra based on the Quality index (Qi). After the Qi is calculated, the spectral data are sorted based on the Qi. This is followed by selecting only the spectra with a high Qi index and comparing the average of all the spatially acquired spectra. This results in an improvement in the spectral signal-to-noise and higher analytical sensitivity of the built calibration curves.

Black and white porcelain plays a critical role in Chinese decorative porcelain history. It is famous for its decorative styles and techniques, which create a strong black and white color contrast in its appearance. In this study, representative black and white porcelains produced in Shanxi province were analyzed by X-ray fluorescence, Raman spectroscopy, and SEM-EDS. The results show that both Ca-rich (~5.33 wt%) and Ca-poor (~1.99 wt%) glazes were used leading to quite different microstructures. The pigment particles of Ca-rich glazes are characterized by small size (≤2 μm), wide distribution, and tightly wrapped by anorthite. In contrast, they are larger (≥2 μm) and tightly cumulated together in Ca-poor glazes. Hematite is the major crystal in pigment, double-substituted by Al and Ti. The Al/Fe ratios are similar, but Ti/Fe ratios are quite different: They do not exceed 0.03% in Ca-poor glazes, whereas they reach 0.12% in Ca-rich glazes, suggesting that the origin of the pigments must be different. Al-rich mineral such as kaolin was added to the pigment preparation in Ca-rich glazes. The color of the pattern is mainly influenced by the size, quantity, and concentration of brown Ti-doping hematite, as well as the thickness of the glaze layer and other crystals and Fe ions. The fired atmosphere of Ca-rich glaze type seems less oxidizing than for Ca-poor glaze type. Overall, the results confirm that black and white porcelain has a variety of production techniques, which is attributed to the craftsman adjusting the techniques according to the composition of raw materials.

Macro-Raman mapping is an approach that allows to obtain high-resolution molecular maps of artefacts, over an area of several square centimetres. The method is based on recording thousands of spectra in a grid. The main drawback of this method is that it is very time consuming. A straightforward approach to reduce the measurement time is achieved by reducing the number of points that are measured. Not all points of the map are equally informative: Pixels that are surrounded by similar points might be less interesting to measure. Therefore, an algorithm is proposed to select where to measure and which points to omit. The missing pixels can be filled in a posteriori, by using a suitable interpolation algorithm. The selection of the omitted pixels can be performed based on information that is available from other analytical techniques. In this case, a selection was made based on the local variances in a colour picture. The approach is evaluated by recording macro-Raman maps of details of a Neptune watercolour painting on paper. In a first stage, the Raman intensities of the scaled and baseline corrected spectra at specific band positions were colour coded and plotted as Raman maps. The interpolation of the Raman maps yielded satisfying results. The image outline could clearly be identified in the maps, and the differently coloured zones were distinguished. Next to this univariate approach, it was demonstrated that also a multivariate data extraction method (principal component analysis) is compatible with the proposed algorithm to measure 25% less datapoints.

The excessive use of pesticides has detrimental effects on the ecosystem, leading to soil contamination and the spread of pollution beyond the targeted areas. Concerns arise regarding the permissible limits of pesticides, typically around 10⁻⁸ mol/L. In this study, we employed surface-enhanced Raman spectroscopy (SERS), a highly sensitive and selective technique, to investigate the behavior of the pesticide ametrine (AMT) on silver colloids. The Ag nanoparticles (AgNPs) exhibited an average size of (26 ± 2) nm and a zeta potential of (−30 ± 1) mV in the absence of AMT, which decreased to (−24 ± 1) mV in the presence of AMT, resulting in mild AgNPs aggregation, with the average diameter of AgNPs increasing to approximately 300 nm. This aggregation is advantageous, as they provide active sites for pesticide detection. Besides, the purification method employed ensured that AMT remained undegraded, and various conformations of AMT were simulated using Ag clusters to study the SERS effect. Comparison with the experimental spectra indicated that the SERS-4 conformer closely resembled the experimental spectrum, suggesting simultaneous interaction between the Ag surface and the sulfur (S) and nitrogen (N) atoms of the AMT triazine ring. Notably, changes in the AMT molecule were observed with pH variations: at pH below 5, hydroxylation occurred, resulting in an Ag–Cl stretching at 241 cm⁻¹ in the SERS spectra. Conversely, at pH above 5 (pH 6–13), the presence of bands at 230 and 219 cm⁻¹ in the SERS spectra indicate the formation of Ag–N and Ag–S bonds, respectively, between the AMT and the AgNPs. Furthermore, the study successfully detected AMT at pH 7, establishing a limit of detection (LOD) of 1.36 × 10⁻⁸ mol/L (3 ppb) based on the SERS spectra. These findings underscore the applicability of the SERS technique in the sensitive and selective detection of AMT, offering a promising approach for monitoring the presence of this pesticide in environmental samples.

In 1949, Almada Negreiros painted at the maritime station of Rocha do Conde de Óbidos, in Lisbon, six monumental mural paintings, which are considered as his highest artistic achievement. On these paintings, he resorted to a bright colourful palette, which needs to be studied to support conservation and preservation of these artworks for future generations. Among the pigments under study within project ALMADA, the identification of the green samples is the most challenging, as Almada Negreiros seems to have explored different hues by using simultaneously inorganic (e.g., emerald green, Scheele's green and viridian) as well as organo-synthetic pigments that were rather unusual when employing a traditional mural painting technique (e.g., PG7 and PG8). Moreover, he seems to have admixed white (e.g., titanium white) or blue pigments (e.g., ultramarine) to modify the hues. The different colourants found, as well as the use of mixtures of pigments, hints that Almada Negreiros was keen on experimenting and applying relatively novel painting materials. Raman spectroscopy, given its ability to identify inorganic as well as organic components, is a key analytical tool to discriminate between all these compounds. The findings were also supported by complimentary analytical techniques, including colourimetry, handheld X-ray fluorescence spectroscopy (h-XRF) and micro-Fourier-transform infrared spectroscopy (μ-FT-IR). Identification of the green pigments by Raman spectroscopy is, however, not always straightforward, and it is demonstrated how changes in relative band intensities and band broadening can point to mixtures, where the Raman spectral features of some compounds can easily be overseen in the spectrum.