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This work communicates cavity ring-down spectroscopy (CRDS) of methylidyne (CH) in a chemiluminescent plasma that is produced in a microwave cavity. Of interest are the rotational lines of the 0-0 vibrational transition for the A–X band and the 1-0 vibrational transition for the B–X band. The reported investigations originate from research on the CH radical in 1996, which constituted the first case of applying CRDS to the CH radical. The report also includes a recent analysis that shows excellent agreement of the measured and computed data, and it communicates CH line strength data. The CH radical is an important diatomic molecule in hydrocarbon combustion diagnosis and the analysis of stellar plasma emissions, to name just two examples of analytical plasma chemistry. [ABSTRACT FROM AUTHOR]

• Synthesized Ru(II) complexes with Mepic and Hpic in MeOH and water solutions. • Complexes showed nearly identical trans (Cl)-RuCl 2 (dmso- S) 2 geometries. • Water crucial for Hpic in 2 ·H 2 O to retain H+ during crystallization. • 1 ·0·25H 2 O unstable in DMSO; 2 ·H 2 O stable because Hpic becomes a negative bidentate ligand, pic–. • 1 ·0·25H 2 O thermally unstable in water, forming MeOH, although free Mepic stable. Methyl picolinate (Mepic) is a starting material in the synthesis of several organic materials and enzymes. Notably, Mepic-ligand-based complexes with metals such as Zn(II), Cd(II), Ru(II), and Rh(III) have garnered attention for catalysis; however, Ru(II)–Mepic complexes remain structurally unexplored. In this study, trans (Cl)-[RuCl 2 (dmso- S) 2 (Mepic)]·0·25H 2 O (1 ·0·25H 2 O, dmso = dimethyl sulfoxide) was produced in a satisfactory yield (80%) via the reaction of trans (Cl)-[RuCl 2 (dmso- S) 4 ] with neutral N,O -ligand Mepic in methanol (MeOH) at room temperature. The use of picolinic acid (Hpic) instead of Mepic in H 2 O-ethanol (EtOH) produced the corresponding complex— trans (Cl)-[RuCl 2 (dmso- S) 2 (Hpic)]·H 2 O (2 ·H 2 O)—with a slightly higher yield (82%). Crystal structure analysis of 1 ·0·25H 2 O and 2 ·H 2 O revealed that each chelating ligand coordinated to Ru2+ via pyridyl- N and carbonyl- O atoms and Hpic acted as a neutral bidentate ligand in 2. In DMSO, 1 was labile and released Mepic to form [RuCl 2 (dmso) 4 ], owing to the hemilability of N,O -ligand Mepic. In contrast, 2 was inert in DMSO because H+ was released from Hpic in solution, forming the anionic mono(pic)Ru complex— trans (Cl)-[RuCl 2 (dmso- S) 2 (pic- κ 2 N,O–)]−. 1H NMR and UV–Vis spectroscopic studies showed that 2 also generated the anionic mono(pic)Ru complex in aqueous solutions. Although free Mepic is inert in water, 1 underwent thermal hydrolysis in water to produce free MeOH. The dissociation of monodentate ligands was also observed in the thermal hydrolysis of 1. Thus, it was a complicated reaction. The reaction of 1 with equimolar OH− in water quickly and selectively yielded the same complex and a MeOH molecule. Our study will assist in assessing the catalytic potential of this complex and related systems. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • Wavelength modulation spectroscopy of a QCL in intermittent continuous wave operation is demonstrated for the first time. • Heat dissipation of the QCL is largely reduced at the WMS-iCW mode, eliminating the necessity of forced cooling. • The minimum detection limit of 4.5 parts per billion (ppb) for NO is achieved with an average time of 80 s. Operating quantum cascade lasers (QCLs) in intermittent continuous wave (iCW) shows the merit of a broader frequency tuning range and lower heat dissipation compared to the continuous wave (CW) operation. We demonstrate for the first time wavelength modulation spectroscopy (WMS) of a QCL in iCW operation for sensitive gas detection. A strong absorption line of nitric oxide (NO) at 5.18 μm is exploited by a QCL in iCW mode, which periodically switches off the QCL between individual laser scans. The generated thermal chirp dominates the laser frequency tuning, resulting in a broader spectral coverage of more than 2 cm−1 at a scanning rate of 1 kHz. In addition, a high-frequency dither (50 kHz) is supposed onto this iCW injection current to introduce the harmonic signals that arise from gas absorption. At the WMS-iCW operation of the QCL, we have obtained a minimum detection limit of 4.5 ppb at an averaging time of 80 s, which is improved significantly compared to 130 ppb achieved by direct absorption spectroscopy at the same averaging time using the identical optical setup, without external forced air- or water-cooling. Our method provides a promising method for sensor miniaturization and field application. [ABSTRACT FROM AUTHOR]

• Analyzed a high resolution 13CH 4 absorption spectrum at 298 K in the 4970–5300 cm−1 region. • Theoretically modelled 1548 line positions to an rms of 0.0017 cm−1. • Successfully fit 674 experimental line intensities to an rms of 7 %. • Assigned and compiled experimental and theoretical line lists at 296 K. The absorption spectrum of the 13CH 4 methane isotopologue was recorded on a Bruker IFS-125HR Fourier transform spectrometer at 298 K in the 4970–6200 cm−1 range. In this paper we report the results of assignment and modelling of the line positions and intensities of 13CH 4 in the range of weaker absorption between 4970 and 5300 cm−1, corresponding to the lower part of Tetradecad, dominated by the 4ν 4 band system near 5180 cm−1. The empirical list in this spectral range contains 1642 lines. Using an effective Hamiltonian initially derived from the analyses of cold Fourier transform (4970–5853 cm−1) and laser direct absorption (5853–6200 cm−1) spectra of the 13CH 4 , we assigned 1600 lines belonging to four bands of the Tetradecad up to J max =16. The 1548 line positions were fitted with an rms deviation of 1.7 × 10−3 cm−1. Measured line intensities were modeled for 674 transitions using the effective dipole transition moments to an rms deviation of about 7 %. The new data were used for the simultaneous global fit of the 13CH 4 Hamiltonian parameters for the {Ground state / Dyad / Pentad / Octad / Tetradecad} system and the dipole moment parameters for the {Ground state - Tetradecad} system. [ABSTRACT FROM AUTHOR]

• Five FTS spectra of ammonia highly enriched in 15NH 3 analyzed between 3900 and 6350 cm-1. • >9500 absorption lines are measured and assigned by comparison to an ab initio calculated line list available in the literature. • All the assignments are validated by using lower state combination difference relations. • Overall, 3544 15NH 3 transitions are assigned to 32 vibrational bands, all but four of them being new. • The empirical energy value of 1242 upper state energy levels is determined. • The assigned transitions represent 94.5 % of the room temperature 15NH 3 integrated absorption in the region. • A recommended line list for ammonia in natural isotopic abundance is provided for the studied region. Following previous contributions dedicated to the main isotopologue, 14NH 3 , in the present work, we examine the 15NH 3 absorption spectrum between 3950 and 6350 cm-1 in order to elaborate an absorption line list for ammonia in natural isotopic abundance. For this purpose, several room temperature Fourier Transform absorption spectra of ammonia highly enriched in 15NH 3 measured in the 90′s and available from the Kitt Peak data centre have been analysed. In addition, a more recent high-resolution spectrum recorded in Brussels between 4150 and 4600 cm-1 is also considered. The spectra were divided in three separate intervals (3900–4706, 4706–5650 and 5650–6350 cm-1) for which experimental lists including 3506, 3788, and 2317 lines, respectively, were retrieved and treated independently. By comparison with an a b initio line list (the BYTe list) and systematically validating the assignments by using lower state combination difference relations (LSCD), 2013, 1771 and 570 transitions could be assigned in the three regions, respectively. They belong to 16, 22, and 10 bands and correspond to 98.5, 92.6 and 78.6 % of the experimental intensities in the region, respectively. For comparison, only four 15NH 3 bands were previously assigned in the literature in the entire studied region. The obtained 15NH 3 assigned line lists were gathered with the previously elaborated line list of the main isotopologue to produce a recommended line list for natural ammonia between 3900 and 6350 cm-1. [Display omitted] [ABSTRACT FROM AUTHOR]

• Measured high-resolution Air-H 2 O absorption from 300 to 1300 K. • Building on our pure-H 2 O database, we determined 7088 parameters for 3366 transitions using speed dependent Voigt parameters. • Improved RMS absorbance error by a factor of 4.2 on average across all measurements. We present broadband dual frequency comb laser absorption measurements of 2 % H 2 O (natural isotopic abundance of 99.7 % H 2 16O) in air from 6600 to 7650 cm−1 (1307–1515 nm) with a spectral point spacing of 0.0068 cm−1. Twenty-nine datasets were collected at temperatures between 300 and 1300 K (±0.82 % average uncertainty) and pressures ranging from 20 to 600 Torr (±0.25 %) with an average residual absorbance noise of 8.0E-4 across the spectrum for all measurements. We fit measurements using a quadratic speed-dependent Voigt profile to determine 7088 absorption parameters for 3366 individual transitions found in HITRAN2020. These measurements build on the line strength, line center, self-broadening, and self-shift parameters determined in the Part I companion of this work. Here we measure air-broadened width (with temperature- and speed-dependence) and air pressure shift (with temperature-dependence) parameters. Various trends are explored for extrapolation to weak transitions that were not covered in this work. Improvements made in this work are predominantly due to the inclusion of air pressure shift temperature dependence values. In aggregate, these updates improved RMS absorbance error by a factor of 4.2 on average, and the remaining residual is predominantly spectral noise. This updated database improves high-temperature spectroscopic knowledge across the 6600-7650 cm−1 region of H 2 O absorption. [ABSTRACT FROM AUTHOR]

Abstract Background A force applied during orthodontic treatment induces inflammation to root area and lead to root resorption known as orthodontically induced inflammatory root resorption (OIIRR). Dentine sialophosphoprotein (DSPP) is one of the most abundant non-collagenous proteins in dentine that was released into gingival crevicular fluid (GCF) during OIIRR. The aim of this research is to compare DSPP detection using the univariate and multivariate analysis in predicting classification level of root resorption. Methods The subjects for this study consisted of 30 patients in 3 group classified as normal, mild, and severe groups of OIIRR. The GCF samples were taken from upper permanent central incisors in the normal and mild group while the upper primary second molars in the severe group. The DSPP qualitative detection limit was determined by analyzing the whole absorption spectrum utilizing multivariate analysis embedded with different preprocessing method. The multivariate analysis represents the multi-wavelength spectrum while univariate analyzes the absorption of a single wavelength. Results The results showed that the multivariate analysis technique using partial least square-discriminate analysis (PLS-DA) with the preprocess method has successfully improved in classification prediction for the normal and mild group at 0.88 percent accuracy. The multivariate using PLS-DA algorithm with Mean Center preprocess method was able to predict normal and mild tooth resorption classes better than the univariate analysis. The classification parameters have improved in term of the specificity, precision and accuracy. Conclusion Therefore, the multivariate analysis helps to predict an early detection of tooth resorption complimenting the sensitivity of the univariate analysis. Trial registration NCT 05077878 (14/10/2021).

Introduction: The Bouguer-Lambert-Beer law is widely used as the fundamental equation for quantification in absorption spectroscopy. However, deviations from the Bouguer-Lambert-Beer law have also been observed, such as chemical deviation and light scattering effect. While it has been proven and shown that the Bouguer-Lambert-Beer law is valid only under very restricted limitations, there are only a few alternatives of analytical models to this law. Based on the observation in the experiments, we propose a novel model to solve the problem of chemical deviation and light scattering effect.Methods: To test the proposed model, a systematic verification was conducted using potassium dichromate solutions and two types of microalgae suspensions with varying concentrations and path lengths.Results: Our proposed model demonstrated excellent performance, with a correlation coefficient (R2) exceeding 0.995 for all tested materials, significantly surpassing the Bouguer-Lambert-Beer law, which had an R2 as low as 0.94. Our results confirm that the absorbance of pure pigment solutions follows the Bouguer-Lambert-Beer law, while the microalgae suspensions do not due to the light scattering effect. We also show that this scattering effect leads to huge deviations for the commonly used linear scaling of the spectra, and we provide a better solution based on the proposed model.Discussion: This work provides a powerful tool for chemical analysis and especially for the quantification of microorganisms, such as the concentration of biomass or intracellular biomolecules. Not only the high accuracy but also the simplicity of the model makes it a practical alternative to the existing Bouguer-Lambert-Beer law.

A tunable diode laser absorption spectroscopy (TDLAS)-based spectrometer employing a mid-infrared (Mid-IR) interband cascade laser (ICL) was developed and used to determine pressure broadening coefficients of two NO absorption transitions at 1914.98 cm−1 and 1915.76 cm−1 in the fundamental (1←0) band (R11.5 Ω1/2 and Ω3/2) for CO2, N2, Ar, O2, He, and H2. For the first time, a reliable and consistent set of six different pressure-broadening coefficients for the NO line has been measured by a consistent approach covering pressures from 100 to 970 mbar at a temperature of 294 K. Air pressure broadening has been calculated based on N2 and O2 coefficients. The stated pressure-broadening coefficients for N2, CO2, Ar, H2, O2, He, and Air have relative errors in the 0.5–1.5% range. For CO2 and H2, broadening results of NO (1←0) band (R11.5 Ω1/2 and Ω3/2) lines are reported for the first time. The results are also compared to previously available literature data. It was found that the broadening coefficients for O2 and Air are in agreement with literature values, whereas results for Ar and He show larger differences. [ABSTRACT FROM AUTHOR]

The line width of different line shapes is a very important parameter in absorption spectroscopy sensing techniques. Based on the high sensitivity and low noise properties of wavelength modulation spectroscopy, we report a novel line width measurement method. After theoretically proving the relationship between line width, modulation amplitude and the amplitude of the second harmonic at the center frequency, the absorption lines of CH4 near 6046.96 cm−1 and CO2 4989.97 cm−1 were chosen for simulation, and the relative errors of the line width between our method and theoretical data were kept at about 1%. A distributed feedback laser diode operating near 1653 nm with three different concentrations of CH4 was used for experimental validation, and the results were consistent with the numerical simulation. Additionally, since only the peaks of second harmonic need to be measured, the advantages of wavelength modulation can be utilized while reducing the difficulty of data acquisition. [ABSTRACT FROM AUTHOR]

A contactless laser hygrometer based on light absorption by H2O molecules at 1392.5 nm is described. However, measurement results can be affected by optical noise when applied to an atmospheric tunnel or glass cuvette. The noises (occurring in the form of periodic fringes in the recorded spectrum) come from unexpected interference of the light beams reflected from surfaces of the windows or other optical elements. The method of their suppression is described in this article. It is based on wavelength modulation and signal averaging over the fringes period. Also, an experiment confirming the usefulness of this method is described here. [ABSTRACT FROM AUTHOR]

We have developed a system for bacteria identification based on absorption spectroscopy in the mid‐infrared spectral range. The data collected are analyzed with a deep learning algorithm. It is based on a neural‐network model which takes one‐dimensional signal vectors and outputs a probability score of identification of a bacterium type by extracting micro and macro scale features, using convolutions and nonlinear operations. The results are achieved in real time and do not require any offline postprocessing. The study was done on 12 of the most common bacteria usually seen in clinical microbiology laboratories. The system sensitivity is 0.94 ± 0.04, with a specificity of 0.95 ± 0.02. The system can be extended to additional bacterium types and variants with no change to its hardware or software, but only updating the model's parameters. The system's accuracy, size, ease of operation and low cost make it suitable for use in any type of clinical setting. [ABSTRACT FROM AUTHOR]

The low water solubility of baricitinib (BCT) limits the development of new formulations for the topical delivery of the drug. The aims of this study were to assess the solubility of BCT in different solvents, including Transcutol, a biocompatible permeation enhancer that is miscible in water, to evaluate the drug uptake in human skin and porcine tissues (sclera, cornea, oral, sublingual, and vaginal), and to subsequently extract the drug from the tissues so as to determine the drug recovery using in vitro techniques. Analytical methods were developed and validated for the quantification of BCT in Transcutol using absorption and fluorescence spectroscopies, which are complementary to each other and permit the detection of the drug across a broad range of concentrations. Results show that Transcutol permits an increased drug solubility, and that BCT is able to penetrate the tissues studied. The solutions of BCT in Transcutol were stable for at least one week. Hence, Transcutol may be a suitable solvent for further development of topical formulations. [ABSTRACT FROM AUTHOR]

This study analyzed the spectral response of EBT3, EBT4, and EBT-XD radiochromic films using absorption spectroscopy. The primary focus was on characterizing the evolution of spectral signatures across a range of absorbed doses, thereby elucidating the unique dose-dependent response profiles of each film type. Ten samples of each film type were subjected to open field irradiation within their designated dose ranges (1-20 Gy for EBT3 and EBT4, 1-50 Gy for EBT-XD). The corresponding absorption spectra were recorded and studied via decomposition and parameterization of dose-dependent spectral features. Lorentzian profiles were employed for spectral decomposition. Each film type displayed unique spectral signatures with distinct absorption peaks: nine for EBT3, eleven for EBT4, and twelve constituent profiles for EBT-XD. Notably, the EBT4 film demonstrated a slight difference in the blue part of the absorption spectrum and a change in the response, relative to its EBT3 predecessor. Orientation dependence of the film spectra was most pronounced for the EBT3 film type, followed by a declining trend across EBT4 and EBT-XD films. Absorption spectroscopy portrayed distinct spectral fingerprints of the studied film types, aiding the selection of the most suitable film for specific applications., (Creative Commons Attribution license.)

The paper presents an analysis and practical study of the temperature and pressure influence on a nondispersive infrared (NDIR) sensor for measuring the concentration of carbon dioxide in human breath. This sensor is used for monitoring patients’ carbon dioxide (CO2) in the exhaled air. High precision and accuracy of CO2 concentration measurements are essential in air sampling systems for breath analysers. They, however, require an analysis of the influence of the human exhaled air pressure and temperature on the NDIR CO2 sensor. Therefore, analyses of the changes in concentration were carried out at a pressure from 986 mbar to 1027 mbar and a temperature from 20°C to 36°C. Finally, corresponding correction coefficients were determined which allow to reduce the relative uncertainty of CO2 sensor measurements results from 19% to below 5%.

Abstract Machine learning methods can be used as robust techniques to provide invaluable information for analyzing biological samples in pharmaceutical industries, such as predicting the concentration of viral particles of interest in biological samples. Here, we utilized both convolutional neural networks (CNNs) and random forests (RFs) to predict the concentration of the samples containing measles, mumps, rubella, and varicella‐zoster viruses (ProQuad®) based on Raman and absorption spectroscopy. We prepared Raman and absorption spectra data sets with known concentration values, then used the Raman and absorption signals individually and together to train RFs and CNNs. We demonstrated that both RFs and CNNs can make predictions with R2 values as high as 95%. We proposed two different networks to jointly use the Raman and absorption spectra, where our results demonstrated that concatenating the Raman and absorption data increases the prediction accuracy compared to using either Raman or absorption spectrum alone. Additionally, we further verified the advantage of using joint Raman‐absorption with principal component analysis. Furthermore, our method can be extended to characterize properties other than concentration, such as the type of viral particles.

Turbulent mixing processes and species transport govern many important properties like stability and pollutant formation of reactive systems. We propose spectrally resolved absorption tomography as a viable tool to quantitatively assess species transport by imaging tracer pulses at high time resolution. Measurements on a gas-assisted solid-fuel combustor operating in air and oxy-fuel atmospheres are presented. The measurements are conducted using a scanning tomographic imaging system that has previously been validated for gas temperature measurements. As the scanning system itself is not able to achieve the necessary time resolution, a phase-locked tomographic scheme is applied, i.e. each measurement beam is acquired separately for several tracer pulses and phase-averaged. Hence, the full 5 kHz time resolution of the underlying tunable diode laser spectroscopy system can be utilized, granting insight into species transport in the recirculation zones as well as the flame brush. Despite a possible influence of the tracer injections on the inner recirculation zone, it is shown that qualitative differences between methane combustion and gas-assisted solid-fuel operating conditions can be detected, and influences of devolatilization as well as volatile combustion become visible.

The Bouguer–Lambert–Beer (BLB) law serves as the fundamental basis for the spectrophotometric determination of pigment content in microalgae. Although it has been observed that the applicability of the BLB law is compromised by the light scattering effect in microalgae suspensions, in-depth research concerning the relationship between the light scattering effect and the accuracy of spectrophotometric pigment determination remains scarce. We hypothesized that (1) the precision of spectrophotometric pigment content determination using the BLB law would diminish with increasing nonlinearity of absorbance, and (2) employing the modified version of the BLB (mBLB) law would yield superior performance. To assess our hypotheses, we cultivated Phaeodactylum tricornutum under varying illumination conditions and nitrogen supplies in controlled indoor experiments, resulting in suspensions with diverse pigment contents. Subsequently, P. tricornutum samples were diluted into subsamples, and spectral measurements were conducted using different combinations of biomass concentrations and path lengths. This was carried out to assess the applicability of the BLB law and the nonlinearity of absorbance. The chlorophyll a and fucoxanthin contents in the samples were analyzed via high-performance liquid chromatography (HPLC) and subsequently used in our modeling. Our findings confirm our hypotheses, showing that the modified BLB law outperforms the original BLB law in terms of the normalized root mean square error (NRMSE): 6.3% for chlorophyll a and 5.8% for fucoxanthin, compared to 8.5% and 7.9%, respectively.

In this study, plant biopolymer gum Acacia is synthesised and chemically modified by fruit extract of black grapes (Vitis vinifera), eggplant (Solanum melongena). Fruits contain functional groups called chromophore which confer colour. It is the region where radiation is absorbed and electron is transferred between two energy states. They absorb UV and/or visible light. They are conjugated unsaturated bonds and responsible for optical and electrical properties. In the present work, optical properties of biopolymer gum Acacia specimen and chromophore induced specimen of the above-mentioned fruits are examined by UV-visible spectroscopy. It is found that light absorption is pronounced in the visible range of spectrum compared to the pure specimen in which absorption is found to be observed in the deep ultraviolet range. Electrical characterisation of the modified gum Acacia biopolymer with grape fruit extract and eggplant extract are observed. Electrical conductivity is enhanced over pure specimen. These properties will be fruitful in dye-sensitised solar cells (DSSCs) application, which is an ongoing extensive research area. [ABSTRACT FROM AUTHOR]

During resonance in resonant cavities, such as those used in laser or cavity ring-down spectroscopes (CRDS), resonant coupling between higher-order transverse modes and fundamental modes can seriously affect the quality of the beam and introduce measurement errors. Several coupling models, such as thermal deformation coupling and scattering coupling, have been established according to existing coupling theory and specific application scenarios; however, these coupling models have not been attributed to a unified theory. In this paper, we reveal that the same resonant coupling excitation factors exist under different types of environmental perturbation. The conditions and range of resonant coupling in a CRDS ring-down cavity are systematically analyzed, and a preferential coupling model of the middle-order modes is proposed. The time-domain characteristics of the CRDS are used in experiments to analyze the resonant coupling between the modes in a weak energy system. The order and coupling range of the middle-order modes involved in resonant coupling are verified using the modal filtering characteristics of the triangular cavity; this paper presents a unified explanation for various types of resonant coupling and also provides a new approach to resonant coupling experiments performed in high-finesse resonant cavities. [ABSTRACT FROM AUTHOR]

Microcombs—generated by coherently pumping nonlinear microresonators—have emerged as a state-of-the-art scheme at the chip scale. Dual-comb spectroscopy (DCS) technology further takes advantage of the miniature system, and has been demonstrated as a powerful tool for real-time and broadband optical sampling of molecular spectra. Here, a novel soliton dual-microcomb generation method by rapid frequency sweep and sideband thermal compensation is put forward, and dual-microcomb optical spectra range beyond 200-nm has been successfully demonstrated in two microresonators with moderate quality factors. Compared to the dual-microcomb with a weak thermal compensation effect, the demonstrated dual-microcomb shows much lower-noise RF beat notes (

Abstract Background Establishing a high-accuracy and non-invasive method is essential for evaluating cardiovascular disease. Skin cholesterol is a novel marker for assessing the risk of atherosclerosis and can be used as an independent risk factor of early assessment of atherosclerotic risk. Methods We propose a non-invasive skin cholesterol detection method based on absorption spectroscopy. Detection reagents specifically bind to skin cholesterol and react with indicator to produce colored products, the skin cholesterol content can be obtained through absorption spectrum information on colored products detected by non-invasive technology. Gas chromatography is used to measure cholesterol extracted from the skin to verify the accuracy and reliability of the non-invasive test method. A total of 342 subjects were divided into normal group (n = 115), disease group (n = 110) and risk group (n = 117). All subjects underwent non-invasive skin cholesterol test. The diagnostic accuracy of the measured value was analyzed by receiver-operating characteristic (ROC) curve. Results The proposed method is able to identify porcine skin containing gradient concentration of cholesterol. The values measured by non-invasive detection method were significantly correlated with gas chromatography measured results (r = 0.9074, n = 73, p

It is important to avoid the overestimation of absorption due to scattering when using absorption spectroscopy to measure scattering samples. We approached this issue by placing the sample inside an integrating sphere (IS) to collect the scattered light in all solid angles but encountered difficulty when determining the absorption coefficient from the absorbance because the light took various paths inside the IS and the sample. Therefore, by ray tracing inside the IS and the sample using Monte Carlo simulations (MC), we estimated the relationship between the absorption, scattering, anisotropy coefficients, and the measured absorbance. Scattering sample M, prepared by mixing polystyrene microspheres with trypan blue solution, and pure trypan blue solution for comparison were used as samples at various concentrations. MC reproduced the measurement results for the absorbance spectrum and its concentration dependence at 591 nm up to the measurement limit value. In addition, the saturated absorbance of sample M was lower than that of the trypan blue solution. This is because, from the distribution of distance d, light passed through the sample estimated by the MC, and more light with smaller d was detected due to scattering for higher concentration, resulting in a smaller increase in absorbance with the absorption coefficient.

Diatomaceous earth (DE) is a sedimentary rock comprising fossilized shells of diatoms, which are a type of algae. The shells of the diatoms are made of silicon dioxide, which is also the main component of DE. DE has excellent moisture absorption and desorption properties and is widely used as an adsorbent, abrasive, insulator, catalyst, and carrier in the stationary phase. It has also been widely studied for its application as a new silicon material in emerging growth fields, such as biosensors. However, because organic matter is adsorbed on the surface of DE, the organic matter must be removed to exploit the properties of mesoporous silica. In this study, the organic matter on the DE surface was removed by alkali treatment to expose the pores and increase the adsorption capacity. Additionally, papain was physisorbed onto DE using a rotator, and l-cysteine was added for papain activation. Under these optimised conditions, the activation of the papain enzyme was effective, resulting in improved DE performance. The adsorption power of DE was correlated with the amount of papain adsorbed, which, in turn, was correlated with its absorbance. Trichloroacetic acid was added to stop the reaction, and the absorbance was measured. The prepared samples were designated as papain/DE (P/DE) complexes. The final concentration of the P/DE was 1 mg/mL. In addition, cross-linked and non-cross-linked P/DE samples were prepared using N-hydroxysuccinimide and water-soluble carbodiimide in a 5:3 ratio and compared. The results showed that surface treatment and functionalisation of DE improved its functionality (enzyme activity), indicating its potential as a new DE material. [Display omitted] • Diatomaceous earth and papain were used to fabricate the functional composites. • The enzyme activity of diatomaceous earth was enhanced by surface treatment. • The absorbance varied with cross-linking and pre-treatment. • The enzyme activity of papain was more efficient in non-cross-linked samples with alkali treatment. [ABSTRACT FROM AUTHOR]

• An improved set of 1117 energy levels of H 2 16 O is retrieved from previous CRDS spectra between 12,969 and 13,418 cm-1. • The set of about 300 energy levels deviating by more than 5 × 10–3 cm-1 from their W2020 value is scrutinized. • For 262 levels, the previously proposed correction of the W2020 value is confirmed. • A line list of 2723 transitions of H 2 16 O , H 2 18O, H 2 17O and HD16O is generated for natural water in the considered region. We have recently devoted two reports to the very weak absorption spectrum of water vapor in the 12,969 – 13,417 cm-1 region by high sensitivity cavity ring down spectroscopy (CRDS) [Vasilchenko et al. J. Quant. Spectrosc. Radiat. Transfer 275 (2021) 107,847; doi.org/10.1016/j.jqsrt.2021.107847; Vasilchenko et al. Molecular Physics e2051762; doi.org/10.1080/00,268,976.2022.2051762]. This spectral interval is important because it includes the region of the oxygen A-band near 760 nm. The achieved sensitivity allowed us to measure lines with intensity on the order of 10–29 cm molecule-1, about two orders of magnitude lower than the detectivity threshold of previous studies. A total of about 240 energy levels of H 2 16 O were newly determined. Our comparison to the W2020 empirical levels [Furtenbacher et al. J. Phys. Chem. Ref. Data 49 (2020) 043,103; doi.org/10.1063/5.0030680] led us to identify and correct about 300 W2020 energy levels of the main isotopologue differing from our energy value by more than 5 × 10–3 cm-1. In the present contribution, we consider in details the sources of the W2020 energy levels to identify the origin of these deviations. We confirm that more than 260 energy levels should be corrected but for the remaining thirty-two levels, the W2020 energy values are in fact, more reliable. As a result, we propose an improved list of energy levels retrieved from the CRDS data and a recommended line list for water vapor in natural isotopic abundance in the 12,969 – 13,417 cm-1 region, mostly based on the CRDS line parameters. [Display omitted] [ABSTRACT FROM AUTHOR]

• The absorption spectra of ethanol were analyzed to choose two optimum wavelengths. • An online measurement system for fuel film thickness was developed. • Evaporation processes of ethanol films on a horizontal quartz plate were studied. • Injection processes of ethanol films on a horizontal quartz plate were investigated. • In-tube flow processes of ethanol films in an inclined quartz tube were discussed. Film thickness as the essential parameter to reveal complicated flow characteristics and heat transfer processes of fuel film, and measurement of fuel film thickness is crucial for optimizing related industrial processes. Here, two optimum wavelengths were chosen by analyzing the absorption spectrum of ethanol at different temperatures. An online measurement system for ethanol film thickness was proposed based on absorption spectroscopy. The validation experiments for measurement accuracy of this system was performed with the calibration tool. Then, the proposed system and imaging method were used to investigate the evaporation processes of ethanol films under different initial thicknesses and injection processes of ethanol under different injection velocities. At last, the in-tube flow processes of ethanol films under different flow rates also were measured by this system. [ABSTRACT FROM AUTHOR]

Cavity ring down spectroscopy (CRDS) is used to measure with unprecedented sensitivity and accuracy the weak water vapour spectrum in the 13,171–13,417 cm−1 region. A total of more than 1400 water lines are rovibrationally assigned to four isotopologues in natural isotopic abundance (H216O, H218O, H217O and HD16O), leading to the determination of 151 new levels and correction of 160 levels. The review of previous experimental works in the region is discussed. The comparison to the recent HITRAN2020 spectroscopic databases and to the W2020 line lists [Furtenbacher et al. J. Phys. Chem. Ref. Data 49 (2020) 043103; doi:] shows important discrepancies both for line positions and line intensities. A significant fraction of the W2020 line positions is inaccurate and shows deviations compared to measurements largely exceeding their claimed error bars. Line intensities are poorly predicted by available ab initio calculations in the considered region. A recommended line list mostly based on the present CRDS measurements is proposed. [ABSTRACT FROM AUTHOR]

Stationary nonlaser gas analyzers have been designed since the 1990s at the Institute of Monitoring of Climatic and Ecological Systems, Siberian Branch, Russian Academy of Sciences, on the basis of the classical differential absorption method for monitoring the content of nitrogen and sulfur oxides in exhaust gases of thermal power plants, which burn natural gas, coal, and fuel oil. The operation of gas analyzers at Russian thermal power plants has shown their high sensitivity, reliability, and ease of maintenance. Based on the differential optical absorption spectroscopy and UV LEDs, a prototype of a portable energy-independent gas analyzer has been designed. It is an effective tool for simultaneous long-path measurements of concentrations of several atmospheric gases. An atomic absorption mercury analyzer has been created, where a capillary lamp with mercury of natural isotopic composition and the transverse Zeeman effect is used as a radiation source. A technique for detecting mercury in different media has been designed; the sensitivity of the analyzer is 14 ng/m3. Its applicability to multipurpose mercury monitoring is shown. [ABSTRACT FROM AUTHOR]

Background: The first application of liquid‐phase broadband cavity‐enhanced absorption spectroscopy (BBCEAS) measurements in food science was made to determine the presence of iron and copper metal in some edible oils. Metal ions in trace amounts, such as iron and copper, have an effect on the oxidative stability of edible oils. The creation of unwanted chemicals is accelerated in the presence of transition metals such as iron and copper, which act as a catalyst in the decomposition of hydrogen peroxides. In general, the rate of oxidation of edible oils can be accelerated, even with trace levels of metal ions. This has an effect on the flavour, odour, and taste of edible oils. As a result, it is critical to determine trace metal concentrations when evaluating oil quality in terms of freshness, stability, and storage. Results: In this work, for the first time, Iron and copper metal were detected in olive oil, sunflower oil, frying rapeseed oil, cold‐pressed olive oil, and cold‐pressed rapeseed oil samples using BBCEAS. Sensitivity and limit of detection (LOD) of conventional spectrophotometer of analysis have been reported as 4.42 × 10−4 cm−1 Hz−½ and 3.3 × 10−2 for Iron and 4.39 × 10−4 cm−1 Hz−½ and 2.8 × 10−2 mg/L for copper. The results of BBCEAS measurements standard solutions produced sensitivity (αmin[t]) and LOD values of 8.86 × 10−6 cm−1 Hz−½ and 2.38 × 10−4 mg/L for Iron and 4.5 × 10−6 cm−1 Hz−½ and 2.1 × 10−4 mg/L for copper, respectively. Conclusion: Overall, the results obtained in this work represent a 116‐fold improvement for iron and 78‐fold for copper in sensitivity compared to conventional absorption spectroscopy measurements. The BBCEAS measurements of iron metal in the edible oil samples did not detect the metal in the olive and sunflower oil samples but did detect it in the other oil samples at parts per billion (ppb) levels. Copper was found to be present in all oil samples. The study demonstrates the suitability of applying the BBCEAS technique to food analysis. [ABSTRACT FROM AUTHOR]

Understanding light-induced processes in biological and human-made molecular systems is one of the main goals of physical chemistry. It has been known for years that the photoinduced dynamics of atomic nuclei can be studied by looking at the vibrational substructure of electronic absorption and emission spectra. However, theoretical simulation is needed to understand how dynamics translates into the spectral features. Here, we review several recent developments in the computation of vibrationally resolved electronic spectra (sometimes simply called 'vibronic' spectra). We present a theoretical approach for computing such spectra beyond the commonly used zero-temperature, Condon, and harmonic approximations. More specifically, we show how the on-the-fly ab initio thawed Gaussian approximation, which partially includes anharmonicity effects, can be combined with the thermo-field dynamics to treat non-zero temperature and with the Herzberg-Teller correction to include non-Condon effects. The combined method, which can treat all three effects, is applied to compute the S1 ← S0 and S2 ← S0 absorption spectra of azulene.

We report a new method of accurately measuring the mid-infrared absorption of fluid analytes using on-chip waveguides that allows measurements to be referenced for noise and drift reduction whilst using only a single external detector. A silicon-on-insulator waveguide circuit integrated with a microfluidic channel is made in which a pair of switches alternate light between an evanescent absorption sensor waveguide and a reference waveguide at a rate of a few kHz, thus allowing low frequency common noise components to be removed from the measurement, and leading to a reduction in the noise floor by a factor of 11 compared to a simple waveguide absorption sensor. The device was verified by using it to detect an Isopropyl alcohol (IPA) absorption peak at a wavelength of 3.77 µm.