Spectra Of Mixtures Research Articles

Beyond Beer's Law: Quasi-Ideal Binary Liquid Mixtures.

We have recorded attenuated total reflection infrared spectra of binary mixtures in the (quasi-)ideal systems benzene-toluene, benzene-carbon tetrachloride, and benzene-cyclohexane. We used two-dimensional correlation spectroscopy, principal component analysis, and multivariate curve resolution to analyze the data. The 2D correlation proves nonlinearities, also in spectral ranges with no obvious deviations from Beer's approximation. The number of principal components is much higher than two and multivariate curve resolution carried out under the assumption of the presence of a third component, results in spectra which only show bands of the original components. The results negate the presence of third components, since any complex should have lower symmetry than the individual molecules and thus more and/or different infrared-active bands in the spectra. Based on Lorentz-Lorenz theory and literature values of the optical constants, we show that the nonlinearities and additional principal components are consequences of local field effects and the polarization of matter by light. Lorentz-Lorenz theory is, however, not able to explain, for example, the different blueshifts of the strong A2u band of benzene in the three mixtures. Obviously, infrared spectroscopy is sensitive to the short-range order around the molecules, which changes with content, their shapes, and their anisotropy.

Deep Learning on Synthesized Sensor Characteristics and Transmission Spectra Enabling MEMS-Based Spectroscopic Gas Analysis beyond the Fourier Transform Limit

Miniaturized Fourier transform infrared spectrometers serve emerging market needs in many applications such as gas analysis. The miniaturization comes at the cost of lower performance than bench-top instrumentation, especially for the spectral resolution. However, higher spectral resolution is needed for better identification of the composition of materials. This article presents a convolutional neural network (CNN) for 3X resolution enhancement of the measured infrared gas spectra using a Fourier transform infrared (FTIR) spectrometer beyond the transform limit. The proposed network extracts a set of high-dimensional features from the input spectra and constructs high-resolution outputs by nonlinear mapping. The network is trained using synthetic transmission spectra of complex gas mixtures and simulated sensor non-idealities such as baseline drifts and non-uniform signal-to-noise ratio. Ten gases that are relevant to the natural and bio gas industry are considered whose mixtures suffer from overlapped features in the mid-infrared spectral range of 2000–4000 cm−1. The network results are presented for both synthetic and experimentally measured spectra using both bench-top and miniaturized MEMS spectrometers, improving the resolution from 60 cm−1 to 20 cm−1 with a mean square error down to 2.4×10−3 in the transmission spectra. The technique supports selective spectral analysis based on miniaturized MEMS spectrometers.

Effect of a Symbiotic Mixture on Fecal Microbiota in Pediatric Patients Suffering of Functional Abdominal Pain Disorders

(1) Background: Functional abdominal pain disorders (FAPDs) represent one of the main etiologies of chronic abdominal pain in the pediatric population. A wide spectrum of probiotic or prebiotic mixtures has been evaluated in trials regarding benefits in patients with FAPDs, mainly in the adult population. (2) Methods: This study was interested in evaluating the effect of oral supplementation with a symbiotic mixture on intestinal microbiota in children with functional dyspepsia (FD), irritable bowel syndrome with diarrhea (IBS-D), and irritable bowel syndrome with constipation (IBS-C). A combination of six bacterial strains (Lactobacillus rhamnosus R0011, Lactibacillus casei R0215, Bifidobacterium lactis BI-04, Lactobacillus acidophilus La-14, Bifidobacterium longum BB536, Lactobacillus plantarum R1012) and 210 mg of fructo-oligosaccharides-inulin were administered orally, daily, for 12 weeks and patients were scored for severity of symptoms and fecal microbiota before and after the treatment. (3) Results: The proportion of patients with adequate symptom relief was higher in the IBS-D than in the IBS-C group; however, the difference was not statistically significant (74.4% vs. 61.9%, p = 0.230). There was an increasing proportion of bacterial genera associated with health benefits, for both IBS-C and IBS-D (IBS-C: 31.1 ± 16.7% vs. 47.7 ± 13.5%, p = 0.01; IBS-D: 35.8 ± 16.2% vs. 44.1 ± 15.1%, p = 0.01). (4) Conclusions: Administration of a symbiotic preparation resulted in significant changes to the microbiota and gastrointestinal symptoms in patients with FAPDs.

Dual-comb cavity-mode width and shift spectroscopy

Optical frequency comb spectrometry has become one of the leading fields devising new ways to investigate molecular structure and characterize optical elements due to its advantage in speed and accuracy. In this work we demonstrate the first dual-comb realization of cavity mode-width and mode-dispersion spectroscopies, achieving single-spectrum acquisition time in millisecond range, maintaining high spectral resolution limited by the comb tooth width. Interleaving of a few tens of spectra allows us to measure shapes of 13 kHz-wide enhancement cavity modes and determine their widths and positions with Hz-level precision. Thanks to this we can simultaneously measure the loss and dispersion of both the cavity and the intracavity medium. As a demonstration, we measure spectra of a gas mixture of methane and nitrogen and compare them with a simulation based on the HITRAN database. This novel method has many possible applications, including gas metrology, high-reflectivity mirror characterization or trace gas sensing.

Quantification of Compatibility Between Polymeric Excipients and\xa0Atenolol Using Principal Component Analysis and Hierarchical\xa0Cluster Analysis

An important challenge to overcome in the solid dosage forms technology is the selection of the most biopharmaceutically efficient polymeric excipients. The excipients can be selected, among others, by compatibility studies since incompatibilities between ingredients of the drug formulations adversely affect their bioavailability, stability, efficacy, and safety. Therefore, new, fast, and reliable methods for detecting incompatibility are constantly being sought. Hence, the purpose of this work was to assess the usefulness of a heating, cooling, and reheating differential scanning calorimetry (DSC) program for detecting potential incompatibilities between atenolol, an active pharmaceutical ingredient (API), and polymeric excipients. Hot-stage microscopy (HSM), Fourier transform infrared (FTIR) spectroscopy, and powder X-ray diffraction (PXRD) were used as supporting techniques. Additionally, principal component analysis (PCA) and hierarchical cluster analysis (HCA) served as tools to support the interpretation of the data acquired from the DSC curves and FTIR spectra. As the alterations in the shape of the DSC peak of atenolol which are indicative of incompatibility are visible only on the cooling and reheating curves of the mixtures, the DSC heating–cooling–reheating program was found to be very useful for identifying potential incompatibilities in the binary mixtures of atenolol and polymeric excipients. The melting and recrystallization of atenolol alone and in its mixtures were also confirmed by HSM, while FTIR displayed changes in the spectra of mixtures due to incompatibility. These studies revealed that atenolol is incompatible with hydroxyethylcellulose, hypromellose, and methylcellulose. PXRD measurements at room temperature revealed that the crystallinity of atenolol did not change in these mixtures. However, its crystallinity was reduced in the mixtures previously heated up to 155 °C and then cooled to 25 °C.Graphical abstract

Simultaneous measurement of liquid-film thickness and solute concentration of aqueous solutions of two urea derivatives using NIR absorption.

We present a method to simultaneously measure the film thickness and individual concentrations of two urea derivates (urea CH4N2O and dimethylurea C3H8N2O) mixed in an aqueous solution at constant temperature using near-infrared (NIR) absorption at multiple specific wavelengths. Fourier transform infrared (FTIR) spectra of aqueous mixtures of urea and dimethylurea solutions were recorded in the 1250-2500 nm wavelength range in thin-layer quartz cuvettes at room temperature. The spectra reveal suitable detection wavelengths, i.e., 1450, 1933, 2200, and 2270 nm, for which both the absorption coefficient and its variation with the species concentration are large enough to achieve satisfactory detection sensitivity and selectivity. For validation measurements, samples were prepared in thin-layer quartz transmission cells with known path lengths and mixture compositions in the range 100-1000 µm and 0-40 wt.%, respectively. Film thickness and mass fractions of both species were determined from measured absorbance ratios in the determined characteristic wavelength bands.

VIS-IR Spectroscopy of Mixtures of Water Ice, Organic Matter, and Opaque Mineral in Support of Small Body Remote Sensing Observations

Visual-to-infrared (VIS-IR) remote sensing observations of different classes of outer solar system objects indicate the presence of water ice and organics. Here, we present laboratory reflectance spectra in the 0.5–4.2 μm spectral range of binary particulate mixtures of water ice, organics analogue (kerite), and an opaque iron sulphide phase (pyrrhotite) to investigate the spectral effects of varying mixing ratios, endmember grain size, and mixing modality. The laboratory spectra are also compared to different implementations of the Hapke reflectance model (Hapke, 2012). We find that minor amounts (≲1 wt%) of kerite (investigated grain sizes of 45–63 μm and <25 μm) can remain undetected when mixed in coarse-grained (67 ± 31 μm) water ice, suggesting that organics similar to meteoritic insoluble organic matter (IOM) might be characterized by larger detectability thresholds. Additionally, our measurements indicate that the VIS absolute reflectance of water ice-containing mixtures is not necessarily monotonically linked to water ice abundance. The latter is better constrained by spectral indicators such as the band depths of water ice VIS-IR diagnostic absorptions and spectral slopes. Simulation of laboratory spectra of intimate mixtures with a semi-empirical formulation of the Hapke model suggests that simplistic assumptions on the endmember grain size distribution and shape may lead to estimated mixing ratios considerably offset from the nominal values. Finally, laboratory spectra of water ice grains with fine-grained pyrrhotite inclusions (intraparticle mixture) have been positively compared with a modified version of the Hapke model from Lucey and Riner (2011).

Effect of Cysteine in Stimulating Some Active Compounds in Garlic Callus Under Different Light Spectra in Vitro

This study was conducted in tissue culture laboratories, Faculty of agriculture, University of Kufa in 2020. The experiment included studying the effect of two factors: type of light: (mixture spectra of red and blue LED R16 : B2), (Fluorescent : normal white light) in interaction with different concentrations of cysteine( 0, 50, and 100 mg.L-1). A completely randomized design (C.R.D) were used with two factor and three replicates. The combined spectra (LED R16:B2) increased the active compounds Di-allyldisulfide and Vinyldithiin (131.33,121.41μg.g-1 F.W. ) respectively. Cysteine (100 mg.L-1) was significantly superior compare to other treatments in producing Di-allyldisulfide and Vinyldithiin content (158.87, 144.35 μg.g-1 F.W) respectively. Results also indicated that the interaction treatment between (LED R16:B2) and (Cysteine 100 mg.L-1) gave significant increase in Di-allyldisulfide and Vinyldithiin content (184.28, 146.07μg.g-1 F.W) respectively. While the tretment (Fluorescent W) and (Cysteine 50 mg.L-1) gave significant increase in Allicin content (195.38 μg.g-1 F.W).

Chemical information obtained from multicomponent spectra by means of Score-based Quantitative Principal Component Analysis

The Score-based Quantitative Principal Component Analysis (SQPCA) has been employed to extract chemical information from a multicomponent spectrum in the presence of unknown interfering compounds. Whereas commonly used quantification chemometric methods usually concern rather large data sets, the SQPCA utilizes, in general sense, few reference standards for which determining the property in a new sample is of interest. The procedure is proposed as an alternative to building a reliable calibration model based on multiple measurements. Instead, the model of synthetic mixture spectra set using the linear combination of the reference signals with various relative concentration of compounds is initiated for Principal Component Analysis (PCA) purpose. In this paper, a new application of the SQPCA to solve a challenging problem of a single analyte quantitation in a complex mixture without concern for the other components has been developed. The effectiveness of the method is demonstrated in terms of the quantitation analysis of two real experimental data sets with overlapped spectral compounds, coming from two techniques – fluorescence spectroscopy and nuclear magnetic resonance spectroscopy. The performance of the approach is also compared with the results available in the literature for these data sets. Furthermore, the guidelines are given for how to create the user-friendly, rapid procedure with the potential in many chemical applications.

SIMULTANEOUS DETERMINATION OF PARACETAMOL AND TAPENTADOL IN TABLETS BY RATIO SPECTRA DERIVATIVE SPECTROPHOTOMETRY

The application of the ratio spectra derivative spectrophotometry to the simultaneous determination of Paracetamol (PCM) and Tapentadol (TAP) in combined pharmaceutical tablets is presented. The spectrophotometric procedure is based on the use of the first derivative of the ratio spectra obtained by dividing the absorption spectrum of the binary mixtures by a standard spectrum of one of the compounds. The first derivative amplitudes were measured at 220 and 232 nm for the assay of TAP and PCM, respectively. Calibration graphs were established for 1-5 μg mL-1 for TAP and 6.5-32.5 μg mL-1 for PCM in binary mixture. The detection limits for TAP and PCM were found 0.098 and 0.595 μg mL-1, respectively, while the quantification limits were 0.298 μg mL-1 for TAP and 1.805 μg/ml for PCM. The relative standard deviations were found to be less than 2%, indicating reasonable repeatability of both methods. The proposed methods were hence validated as per ICH guidelines and successfully applied to the determination of these drugs in commercial tablets.

Development and Verification of Conformer-Specific Vibrational Spectroscopy.

Conformers have similar vibrational structures both in neutral (S0) and cationic (D0) states owing to the comparable force fields between their nuclei. Nevertheless, there is a continuous development of vibrational spectroscopic techniques to rigorously identify individual conformers in the designated molecule but only in the S0 state. We developed an inventive conformer-specific vibrational spectroscopic technique to measure identifiable vibrational spectra of individual conformers in both S0 and D0 states. We measured isomer-specific vibrational spectra in both states for gas-phase acetone and oxetane isomers from a solution with azeotropic composition to verify the proposed techniques that are based on infrared (IR) resonant vacuum ultraviolet mass-analyzed threshold ionization (VUV-MATI) spectroscopy. The measured IR dip VUV-MATI and IR hole-burn VUV-MATI spectra for each isomer, which correspond to isomer-specific vibrational spectra in both states, can be represented by IR-resonant VUV photoionization and one-photon VUV-MATI spectra of the binary mixture, respectively, under supersonic expansion conditions. The partial pressures of the individual isomers in the binary mixture with different mole fractions estimated according to the relative peak intensities in the measured spectra provide insights on solute-solvent interactions. We suggest that the verified IR-resonant VUV-MATI spectroscopy can form the basis of effective schemes toward conformational chemistry.

Orientation Averaged Visible/Near‐Infrared and Mid‐Infrared Optical Constants of Hydrous Ca‐Sulfates: Gypsum and Bassanite

AbstractThe hydrous Ca‐sulfates, gypsum and bassanite, have been detected on Mars using both visible/near‐infrared (VNIR) remote sensing measurements and in‐situ rover‐based mineralogical measurements. Understanding the distributions and abundances of minerals on the Martian surface from remote sensing data is important in evaluating ancient Martian environments. Optical constants are critical input parameters in radiative transfer theory, which allows for the extraction of mineral abundances from a mixture spectrum. We have derived VNIR (0.35–2.5 μm, at 10 nm spectral sampling) optical constants of gypsum and bassanite powders using radiative transfer theory and laboratory reflectance spectra of separated size fractions as well as multiple phase angles. In addition, the MIR (2.5–25 μm, or 4,000–400 cm−1, at 2 cm−1 spectral sampling) orientation averaged optical constants of gypsum and bassanite were generated using the classical Lorentz‐Lorenz dispersion theory. We compare the optical constants of gypsum derived in this work with previously published estimates and note both similarities and differences. The optical constants derived in this work will assist in modeling VNIR reflectance spectra and quantifying mineral abundances from mineral mixtures.

Molecular simulation of Rayleigh-Brillouin scattering in binary gas mixtures and extraction of the rotational relaxation numbers.

Rayleigh-Brillouin scattering (RBS) in gases has received considerable attention due to its applications in LIDAR (light detection and ranging) remote sensing and gas property measurements. In most cases, the RBS spectra in the kinetic regime are calculated based on kinetic model equations, which are difficult to be applied to complex gas mixtures. In this work, we employ two widely used molecular simulation methods, i.e., direct simulation Monte Carlo (DSMC) and molecular dynamics (MD), to calculate the spontaneous RBS spectra of binary gas mixtures. We validate these two methods by comparing the simulation results for mixtures of argon and helium with the experimental results. Then we extend the RBS calculations to gas mixtures involving polyatomic gases. The rotational relaxation numbers specific to each species pair in DSMC are determined by fitting the DSMC spectra to the MD spectra. Our results show that all the rotational relaxation numbers for air composed of N_{2} and O_{2} increase with temperature in the range of 300-750 K. We further calculate the RBS spectra for binary mixtures composed of N_{2} and one noble monatomic gas, and the simulation results show that the rotational relaxation of N_{2} is greatly affected by the mass of the noble gas atoms. This work demonstrates that RBS is a promising and alternative way to study the rotational relaxation process in gas mixtures.

A Numerical Procedure for Multivariate Calibration Using Heteroscedastic Principal Components Regression

Many methods have been developed to allow for consideration of measurement errors during multivariate data analyses. The incorporation of the error structure into the analytical framework, usually described in terms of the covariance matrix of measurement errors, can provide better model estimation and prediction. However, little effort has been made to evaluate the effects of heteroscedastic measurement uncertainties on multivariate analyses when the covariance matrix of measurement errors changes with the measurement conditions. For this reason, the present work describes a new numerical procedure for analyses of heteroscedastic systems (heteroscedastic principal component regression or H-PCR) that takes into consideration the variations of the covariance matrix of measurement fluctuations. In order to illustrate the proposed approach, near infrared (NIR) spectra of xylene and toluene mixtures were measured at different temperatures and stirring velocities and the obtained data were used to build calibration models with different multivariate techniques, including H-PCR. Modeling of available xylene–toluene NIR data revealed that H-PCR can be used successfully for calibration purposes and that the principal directions obtained with the proposed approach can be quite different from the ones calculated through standard PCR, when heteroscedasticity is disregarded explicitly.

A pilot study for fragment identification using 2D NMR and deep learning.

This paper presents a proof of concept of a method to identify substructures in 2D NMR spectra of mixtures using a bespoke image-based convolutional neural network application. This is done using HSQC and HMBC spectra separately and in combination. The application can reliably detect substructures in pure compounds, using a simple network. Results indicate that it can work for mixtures when trained on pure compounds only. HMBC data and the combination of HMBC and HSQC show better results than HSQC alone in this pilot study.

Modular Synthesis of Tetraurea and Octaurea Macrocycles Encoded with Specific Monomer Sequences

Modular Synthesis of Tetraurea and Octaurea Macrocycles Encoded with Specific Monomer Sequences

Data Preprocessing Method for the Analysis of Spectral Components in the Spectra of Mixtures.

This paper describes a data preprocessing algorithm that can be used to mitigate the effects of interfering spectral components when the goal is to detect the spectrum of unknown components in a mixture of known components or to verify the presence of suspected components in the spectrum of a mixture of known components. The algorithm is both relatively simple and applicable to a wide range of problems in spectroscopy. The range of applicability can be increased by combining the method with other data preprocessing methods, for example derivative spectra, and can also accommodate variability in the spectra of one or more of the known components. Examples of the application of the algorithm to real problems are given for near-infrared analysis of antibiotic drug formulations inside gelatin capsules and mid-infrared analysis of atmospheric pollutants.

Method for Automatic Generation of Indirect Hard Models using crossvalidation (MAGIC) for the spectral analysis of mixture spectra

Indirect Hard Modeling (IHM) is a physics-based method for the quantitative analysis of fluids’ compositions using Raman, IR or NMR spectroscopy. IHM models mixture spectra with a superposition of their corresponding pure component models consisting of a sum of parametrized peak functions. By specifically adjusting parameters of the peak functions, IHM allows to properly handle non-linear effects in the mixture spectra, like peak shifts. However, the accuracy of the predicted compositions using IHM strongly depends on user-decisions regarding the number of peak functions and the chosen peak parameter adjustments. Existing algorithms to overcome this user-dependency choose number of peak functions and peak parameter adjustments independently from each other, based on the error of the spectral fit. As the error of the spectral fit steadily decreases with increasing model complexity, user-defined stopping criteria are still required. We present a Method for Automatic Generation of Indirect Hard Models using Crossvalidation (MAGIC) that jointly chooses number of peak functions and peak parameter adjustments by minimizing the error of the crossvalidated compositions of the calibration spectra. This requires no stopping criterion and leads to models with higher accuracy regarding the predicted compositions, while keeping the model complexity low. We present the advantages of MAGIC in comparison to the existing algorithms for the quantitative analysis of Raman spectra by applying it to exemplary spectra of three different mixtures.

Label-Free and Rapid Detection of Anthrax Protective Antigen by Surface-Enhanced Raman Scattering on Au Nanorods

Aiming at the requirement of ultra-sensitive on-site rapid detection of anthrax protective antigens (PA), we proposed a label-free detection scheme based on surface-enhanced Raman Scattering (SERS) on Au nanorods (AuNRs) substrate that we fabricated. The Raman spectrum of anthrax protective antigen was reported for the first time. The limit of detection (LOD) of PA on the AuNRs was characterized to be 100 pg/mL. To simulate the actual detection of PA in human serum albumin (HSA), the label-free detection of HSA based on the AuNRs SERS substrate was studied in this paper. The characteristic peaks of the obtained HSA spectrum are consistent with the previously reported literature. The SERS label-free detection of PA in HSA solution has also been achieved. The limit of detection of the PA in HSA solution can also reach 100 pg/mL, which is much lower than the PA concentration of 100 μg/mL in human serum after anthrax infection. A good linear relationship between the peak intensity of the mixture spectrum and the logarithm of the concentration of PA was obtained with the correlation coefficient to be 0.9769. Using Principal Component Analysis (PCA) method, the SERS data of PA, HSA and the mixture can be classified into three completely separated areas without overlap. The entire testing process will cost only about eight minutes, which is much faster than the mature technology, such as Enzyme-linked Immunosorbent Assay (ELISA).

Excitation, emission, and synchronous fluorescence for astrochemical applications: Experiments and computer simulations of synchronous spectra of polycyclic aromatic hydrocarbons and their mixtures

Synchronous fluorescence spectroscopy is a variation of the fluorescence technique for detection and characterization of many single ring aromatic organic molecules, polycyclic aromatic hydrocarbons, and fluorescent amino acids among other molecules. To our knowledge this technique has not been used in space exploration. In order to demonstrate the utility of this technique for planetary and astrochemical applications, we present several laboratory experiments and computer simulations with pure samples and mixtures. Computer deconvolution of experimental excitation and emission fluorescence bands is presented and used to generate synchronous spectra. The computer simulation successfully predicts the number of synchronous fluorescence (SF) bands, band shapes, and band maximum wavelengths for any constant wavelength difference (Δλ). To test the simulation, emission, excitation, and synchronous spectra were obtained for anthracene in n-hexane. Excellent agreement is obtained reproducing and finding the origin of the experimental SF bands for values of Δλ between 2 and 100. The excitation, emission, and synchronous (Δλ = 10) spectra of toluene, aniline, naphthalene, acenaphthene, pyrene, and anthracene are obtained. Excitation of a mixture of the six compunds at three wavelengths (249, 266, and 355 nm) produce fluorescence emission spectra identifying some compounds. The synchronous spectrum (Δλ = 10) of the same mixture is presented and assigned based on the synchronous bands of the individual compounds. The synchronous fluorescence technique and the computer simulation method are proposed to complement other techniques in the analysis of fluorescent samples from comets, as well as in missions to planets and satellites of the solar system.