Spectra Of Mixtures Research Articles

Two different spectrophotometric methods for simultaneous determination of binary mixture of atenolol and amlodipine in commercial formulation

Two different spectrophotometric methods for simultaneous determination of binary mixture of atenolol and amlodipine in commercial formulation

VNIR reflectance spectra of silicate-graphite mixtures: The effect of graphite content and particle size

We report the VNIR (350–2500 nm) reflectance spectra of a suite of silicic samples mixed with graphite. We used three end-member materials with different chemical composition in order to have a comprehensive understanding of the effect of opaque minerals on reflectance spectra of silicic rocks. To decouple the effect of granulometry and graphite content on reflectance properties, we first measured the reflectance spectra for each end member at different grainsizes (between ⁓20 to 250 μm). Three selected grainsizes for each end-member were then mixed with graphite in the graphite/end-member weight ratio 1 to 5%. For each spectrum we evaluated the main band parameters (position, area, depth). Moreover, we also proposed and discussed the use of an additional parameter, the band centroid. Our results confirm that graphite mixed with silicate materials reduces albedo and decreases the spectral slopes and the spectral contrast of the mixtures. We discussed the subtle interplay between grain size, graphite content and chemical composition of the mixtures. We showed how graphite decreases the spectral slopes of the graphite-silicate mixtures proportionally to iron content (albedo) of the mixtures: low iron (bright) materials are more sensitive to spectral slope variation (decrease) as a function of graphite content. Finally we show how spectral slope influences the measured band parameters.

Different spectrophotometric methods for simultaneous quantification of lycopene and β-carotene from a binary mixture

UV-VIS spectrophotometric analysis is one of the cheapest and most handy methods used for carotenoids quantification in solutions. According to Lambert-Beer's law, carotenoids concentrations in a mixture are computed using mixture absorbances and characteristic absorption coefficients for pure compounds. This work proposes four methods for simultaneous quantification of two carotenoids using mixture spectral data, physical models of pure and mixtures spectra in acetone-hexane mixture, different wavelengths groups for absorbance of each carotenoid, the spectra overlapping property and isosbestic point presence. Two absorbance factors defined to improve the concentrations equations accuracy and different assumptions in terms of wavelengths groups and contribution of each carotenoid at mixture absorbance are considered. These methods are validated using synthetic mixtures for two carotenoids (lycopene and β-carotene) and two tomato residue extracts using equivalence test as statistical tool. IPM–II–WG6 method gives good correlation from statistical point of view, with medium accuracy errors.

Mass Defect Filter for Removing Noise and Detector Oscillation Artifacts in Centroided Time-of-Flight Mass Spectra.

Spurious peaks in centroided mass spectra resulting from detector oscillation or "ringing" can be identified by their unusual mass defects. Mass defect plots (fractional m/z vs measured m/z) for the single-charge mass spectrum of a pure compound show data points falling along lines with well-defined slopes. Detector oscillation and electronic noise peaks were removed from database spectra of pure compounds and mixtures by eliminating points outside two standard deviations of the slope of the major peaks. No loss of chemical information was observed, even for compounds with isobaric fragment peaks.

Structural analysis of unstable norbixin isomers guided by pure shift nuclear magnetic resonance.

We report the analysis of complex samples obtained during the microwave irradiation/heating of norbixin, which has been identified as a potential therapeutic target for age-related macular degeneration (AMD). In this context, identifying the different isomers that are obtained during its degradation is of primary importance. However, this characterization is challenging because, on the one hand, some of these isomers are unstable, and on the other hand, the 1 H spectra of these isomeric mixtures are poorly resolved. We could successfully apply 1D pure shift experiments to obtain ultrahigh-resolution 1 H nuclear magnetic resonance (NMR) spectra of the norbixin isomer samples and exploit their information content to analyze complementary 2D NMR data and describe accurately their isomeric composition.

Nanostructured (Co x Fe1– x )3–y O4 spinel – mechanochemical synthesis

Abstract The effects of wet-milling mixtures of α-Fe2O3 and cobalt hydroxide Co(OH)2 over a range of Co/Fe ratios for 215 h have been investigated by neutron diffraction and Mössbauer spectroscopy. The starting materials were mixed according to the stoichiometric formula (Co x Fe1 –x )3O4 for values of x = 0.037, 0.071, 0.133, 0.234 and 0.380 (i. e., from ≈ Co0.1Fe2.9O4 to the cobalt spinel CoFe2O4). These studies reveal the formation of a nanostructured, mixed Co–Fe spinel phase with non-stoichiometric composition (Co x Fe1– x )3 –y O4; the defect spinels have refined values x c = 0.04, 0.08 and 0.14 for the mixtures with the lowest Co content (x = 0.037, 0.071 and 0.133) and defect concentrations in the range y ≈ 0.1 –0.2. Both the spinel phase and un-reacted α-Fe2O3 are found to occur in the neutron diffraction patterns and Mössbauer spectra for the high Co content mixtures x = 0.234 and x = 0.380. Rietveld refinements of the neutron data indicate that the Co atoms predominantly occupy the octahedral B sites with vacancies also found to be located on the octahedral B sites. Analyses of the Mössbauer spectra of the milled samples confirm the existence of vacancy defects in the B sites and reveal that the vacancies cause similar effects to those of the Co ions, leading to a higher average charge state per iron atom.

GAN-regularized augmentation strategy for spectral datasets

Abstract Artificial neural networks are used in various fields including spectral unmixing, which is used to determine the proportions of substances involved in a mixture, and achieve promising results. This is especially true if there is a non-linear relationship between the spectra of mixtures and the spectra of the substances involved (pure spectra). To achieve sufficient results, neural networks need lots of representative training data. We present a method that extends existing training data for spectral unmixing consisting of spectra of mixtures by learning the mixing characteristic using an artificial neural network. Spectral variability is considered by random inputs. The network structure used is a generative adversarial net that takes the dependence on the abundances of pure substances into account by an additional term in its objective function, which is minimized during training. After training further data for abundance vectors for which there is no real measurement data in the original training dataset can be generated. A neural network trained with the augmented training dataset shows better performance in spectral unmixing compared to being trained with the original dataset. The presented network structure improves already existing results obtained with a generative convolutional neural network, which is superior to model-based approaches.

Predicting the uniqueness of single non-negative profiles estimated by multivariate curve resolution methods

In many kinds of chemical data, one or more species are unknown and the only efficient way to identify and/or quantify them is by mathematical resolution of the mixture spectra. The major problem with such mathematical decompositions is the possibility of obtaining a range of feasible solutions instead of a unique solution due to insufficient prior information about the system under study. However, even with the minimal non-negativity assumptions, there may be some levels of uniqueness, i.e., full/partial/fractional, in the results of the bilinear decomposition of chemical data which is very important to detect. In this study, a procedure is proposed to predict the uniqueness of the resolved non-negative profiles obtained by MCR-ALS (or analogous methods like NMF, EFA, SIMPLISMA, ITTFA, HELP, etc.). This uniqueness prediction is based on the data-based uniqueness (DBU) theorem and the general rule of uniqueness (GRU) presented in previous studies. The proposed procedure is easy to implement, has no additional computational cost, and is general for different systems with any number of components. Several simulated and experimental datasets containing different numbers of components were used to examine and evaluate the proposed procedure.

Controls on turnover of marine dissolved organic matter—testing the null hypothesis of purely concentration‐driven uptake: Comment on Shen and Benner, “Molecular properties are a primary control on the microbial utilization of dissolved organic matter in the ocean”

Controls on turnover of marine dissolved organic matter—testing the null hypothesis of purely concentration‐driven uptake: Comment on Shen and Benner, “Molecular properties are a primary control on the microbial utilization of dissolved organic matter in the ocean”

Data on FTIR spectra of mixtures of sodium valproate (VPA) and histones H1 and H3

Valproic acid/sodium valproate (VPA), a drug primarily used for treatment of seizure disorders, is recognized as an efficient epigenetic agent, inducing inhibition of histone deacetylases, promoting changes in the methylation status of DNA and histones, and affecting chromatin structure. In addition to these epigenetic effects, molecular affinity of VPA for histone H1 has been proposed based on thermal denaturation, fluorescence spectroscopy and circular dichroism assays. VPA interactions with DNA and histones using Fourier transform infrared (FTIR) microspectroscopy and high-performance polarization microscopy that are not related to the effects promoted on epigenetic markers have been recently explored. Data in this article provide supplementary information for a better understanding of the resulting FTIR spectra for mixtures of VPA and histones H1 and H3 and of the potential effect of VPA directly on histones that has been reported in the literature.

Mixtures of choline chloride and tetrabutylammonium bromide with imidazole as examples of deep eutectic solvents: their structure by theoretical and experimental investigation

Imidazole based eutectic solvents have been recently proposed as novel solvents and have been synthetized and characterized by different experimental techniques. We studied the structure of two deep eutectic solvents (DESs) based on imidazole and two organic salts (tetrabutylammonium bromide, TBABr, and choline chloride, ChCl). We focused our attention on the microscopic distribution of their components in the liquids by a study of Infrared and Raman spectroscopy and X-ray diffraction. The vibrational spectra of the eutectic mixtures have been analysed with the aim to characterized the nature of the interactions between anions, cations and imidazole. X-ray diffraction pattern has been interpreted on the light of the intermolecular contacts. Vibrational spectra and diffraction data have been compared with the results of computational studies obtained for both the DESs by molecular dynamics and quantum chemistry calculations.

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The IR transmittance spectrum of an isotopic mixture of chlorodifluoromethane (CHF2Cl, Freon-22) with a 33% fraction of 13C and a natural ratio of chlorine isotopes was measured in the frequency range 1400-740 cm–1 with a resolution of 0.001 cm–1 at a temperature of 20C. An ab initio calculation of the structure and sextic potential energy surface and surfaces of the components of the dipole moment has been carried out by the the electronic quantum-mechanical method of Möller-Plesset, MP2/cc-pVTZ. Then the potential was optimized by replacing the harmonic frequencies with the frequencies calculated by the electronic method of coupled clusters, CCSD(T)/aug-cc-pVQZ. The fundamental and combination frequencies were calculated using the operator perturbation theory of Van Vleck (CVPTn) of the second and fourth order (n=2,4). Resonance effects were modeled using an additional variational calculation in the basis up to fourfold VCI excitation (4). The average prediction error for the fundamental frequencies of the 12C isotopologues was ~1.5 cm–1. The achieved accuracy made it possible to reliably predict the isotopic frequency shifts of the 13C isotopologues. It is shown that the strong Fermi resonance ν4/2ν6 dominates in the 12C isotopologues and is practically absent in 13C. The literature assumption [Spectrochim. Acta A, 44: 553] about the splitting of ν1 (CH) due to the resonance ν1/ν2+ν7+ν9 is confirmed. The coefficients of the polyadic quantum number are determined. The analysis made it possible to carry out a preliminary identification of the centers of the vibrational-rotational bands of isotopologues 13CHF235Cl и 13CHF237Cl in the spectrum of the mixture in preparation for individual analyzes of the vibrational-rotational structures of individual vibrational transitions.

Неэмпирический анализ изотопических сдвигов и резонансных эффектов в инфракрасном спектре высокого разрешения фреона-22 (CHF-=SUB=-2-=/SUB=-Cl), обогащенного -=SUP=-13-=/SUP=-C

The IR transmittance spectrum of an isotopic mixture of chlorodifluoromethane (CHF2Cl, Freon-22) with a 33% fraction of 13C and a natural ratio of chlorine isotopes was measured in the frequency range 1400-740 cm–1 with a resolution of 0.001 cm–1 at a temperature of 20C. An ab initio calculation of the structure and sextic potential energy surface and surfaces of the components of the dipole moment has been carried out by the the electronic quantum-mechanical method of Möller-Plesset, MP2/cc-pVTZ. Then the potential was optimized by replacing the harmonic frequencies with the frequencies calculated by the electronic method of coupled clusters, CCSD(T)/aug-cc-pVQZ. The fundamental and combination frequencies were calculated using the operator perturbation theory of Van Vleck (CVPTn) of the second and fourth order (n=2,4). Resonance effects were modeled using an additional variational calculation in the basis up to fourfold VCI excitation (4). The average prediction error for the fundamental frequencies of the 12C isotopologues was ~1.5 cm–1. The achieved accuracy made it possible to reliably predict the isotopic frequency shifts of the 13C isotopologues. It is shown that the strong Fermi resonance ν4/2ν6 dominates in the 12C isotopologues and is practically absent in 13C. The literature assumption [Spectrochim. Acta A, 44: 553] about the splitting of ν1 (CH) due to the resonance ν1/ν2+ν7+ν9 is confirmed. The coefficients of the polyadic quantum number are determined. The analysis made it possible to carry out a preliminary identification of the centers of the vibrational-rotational bands of isotopologues 13CHF235Cl и 13CHF237Cl in the spectrum of the mixture in preparation for individual analyzes of the vibrational-rotational structures of individual vibrational transitions.

Spectrometric Determination of the Total Concentration of Single-Type Analytes Using Conventional Multidimensional Calibrations

Multidimensional calibrations can be used for the spectrometric determination of the total concentration (cΣ) of similar substances; these calibrations relate the generalized signals (AΣ)j measured at different wavelengths (λj) with the concentrations of these analytes (ci) and their absorption coefficients (kij). Such calibrations are conventionally used for the separate determination of analytes, while the ci values are calculated using chemometric algorithms. To find cΣ, one should only take a sum of the found ci values. Despite the simplicity of this type of group analysis, it is rarely used, and its capabilities have not been studied. It is unclear how the accuracy of the cΣ estimate depends on the number of analytical wavelengths (AWLs), the number of standards, and other factors. The purpose of this study was to obtain relevant information using an example of model mixtures of arenes. The absorption spectra of arene mixtures were recorded in the region 230–280 nm, where these spectra are additive. We analyzed 55 hexane solutions containing three to six arenes with a total concentration of 0.1–0.5 mg/mL. The qualitative composition of the model mixtures was considered to compose the matrix of absorption coefficients of individual arenes. The ci values were found by multiple linear regression (MLR, direct calibration). With a sufficiently large number of AWLs, the found ci values were close to zero for arenes absent in the sample and close to the actual ci values for the present arenes. The summation of the found ci gave approximately correct estimates of cΣ (±5%). The single errors of the group analysis were, as a rule, smaller than the errors of the determination of the mixture components. The complication of the model (the introduction of “extra” standards and an increase in the number of AWLs) did not affect the accuracy of the results of group analysis, and the simplification of the model increased errors. If only the most typical standards were used to form the model, the values of kij of which covered the entire range of possible values of kij, the presence of components in the sample that were not taken into account by the simplified model did not lead to a noticeable increase in errors.

BAYESIAN REGRESSION OF OVERLAPPING IBUPROFENPARACETAMOL UV SPECTRA

Bayesian regression has been successfully applied to predict a full spectrum of ibuprofen and paracetamol binary mixture. The Bayesian regression models were constructed using 25 ibuprofen and paracetamol mixture with concentration combinations of 6, 8, 10, 12, and 14 ppm for each ibuprofen and paracetamol. The models were validated using synthetic test solutions to acquire the model’s accuracy and precision. The intercept, slopes, and model mean squared error indicated that paracetamol prediction on the test and sample solution was more reliable than ibuprofen. The recovery ranges and mean squared error for both the test solution and pain relief tablet confirm that the models have good accuracy in predicting ibuprofen and paracetamol binary mixture in the pharmaceutical drug. The measurement was carried out at wavelengths ranging from 220 to 270 nm.

Speed of Sound, Density, Viscosity and Related Thermodynamic Excess Properties of Binary Liquid Mixtures Containing Butyl Carbitol with 1-Butanol, Toluene and Diethylmalonate at 308.15 and 318.15 K

In present communication, measurements of experimental density, viscosity and ultrasonic velocity of binary liquid mixtures of butyl carbitol with 1-butanol, toluene and diethylmalonate have been carried out at 308.15 and 318.15 K at atmospheric pressure over the entire composition range of mole fractions. To study the intermolecular interactions present in these liquid mixtures, thermodynamic parameters like VE, ΔKS, Δη, ΔLf, ΔVf and ΔZ have been calculated. The excess functions and their deviations from ideality have also been correlated using Redlich-Kister type polynomial equation by the method of least-squares. The variations of thermodynamic parameters with composition and temperature have been discussed in terms of molecular interaction in these liquid mixtures. Further, IR spectra of these liquid mixtures have also been recorded and the obtained results have been used to analyze the mixing behaviour of the components.

Interaction of polyvinyl alcohol with cetyltrimethylammonium bromide surfactant and its effect on electrochemical property

Polymer-Surfactant mixed systems have sparked a lot of attention because of their wide range of industrial applications. In the present work, interaction features of the Polymer-Surfactant self-assembled system was computed at various ratios. The interaction between a cationic surfactant Cetyltrimethylammonium bromide (CTAB) and a water soluble polymer polyvinyl alcohol (PVA) was investigated using UV–Visible Spectroscopy, FTIR and Electrochemical investigations. At varied concentrations of PVA/CTAB, the UV–Visible spectrum of the reaction mixture was recorded. In the UV–Visible spectrum, the absorption band was observed at 272 nm. According to the UV–vis spectra the absorbance of PVA/CTAB increased at a lower concentration due to the solubility of the polymer. The ammonium salts distinctive groups were integrated on the polymer according to FTIR data. Atomic force Microscopic studies reveal that CTAB was homogeneously mixed with PVA due to interfacial interaction. The behavior of Cetyltrimethylammonium bromide and PVA mixtures has been studied electrochemically. It has shown relatively higher impedance indicating greater protection. It was revealed to be dependent on the concentrations of both polymer and surfactant.

Influence of intermolecular interactions on the infrared complex indices of refraction for binary liquid mixtures.

This paper investigates the accuracy of deriving the composite optical constants of binary mixtures from only the complex indices of refraction of the neat materials. These optical constants enable the reflectance spectra of the binary mixtures to be modeled for multiple scenarios (e.g., different substrates, thicknesses, volume ratios), which is important for contact and standoff chemical detection. Using volume fractions, each mixture's complex index of refraction was approximated via three different mixing rules. To explore the impact of intermolecular interactions, these predictions are tested by experimental measurements for two representative sets of binary mixtures: (1) tributyl phosphate combined with n-dodecane, a non-polar medium, to represent mixtures which primarily interact via dispersion forces and (2) tributyl phosphate and 1-butanol to represent mixtures with polar functional groups that can also interact via dipole-dipole interactions, including hydrogen bonding. The residuals and the root-mean-square error between the experimental and calculated index values are computed and demonstrate that for miscible liquids in which the average geometry of the cross-interactions can be considered isotropic (e.g., dispersion), the refractive indices of the mixtures can be modeled using composite n and k values derived from volume fractions of the neat liquids. Conversely, in spectral regions where the geometry of the cross-interactions is more restricted and anisotropic (e.g., hydrogen bonding), the calculated n and k values vary from the measured values. The impact of these interactions on the reflectance spectra are then compared by modeling a thin film of the binary mixtures on an aluminum substrate using both the measured and the mathematically computed indices of refraction.

Thermo-physical properties of 1,3-Diaminopropane + alkyl acetate (C1-C4) liquid mixtures: Investigation of molecular interactions by insight of IR spectroscopy and DFT studies

The density (ρ) and speed of sound (u) data of 1,3-Diaminopropane (1,3-DAP) (1) + alkyl acetate (AAc) (C1-C4) (2) mixtures at the temperatures (298.15, 303.15, 308.15, 313.15, and 318.15) K and pressure 0.1 MPa were measured. ρ and u data have been used to calculate excess molar volume (VmE), excess molar isentropic compressibility (ksE), excess ultrasonic speed (uE), excess free volume (VfE), excess available volume (VaE) and excess intermolecular free length (LfE). The result of speed of sound have been analyzed in term of various correlations like Nomoto, Van Dael, Impedance dependence and Schaaff's collision factor theory at temperature 298.15 K. The calculated deviation and excess properties are well fitted with Redlich-Kister polynomial equation and further results were analyzed with the help of the structural, inter and intramolecular interaction aspects. IR spectra of the liquid mixture supported the intermolecular interaction between the 1,3-DAP and AAc molecules through shifting of the position of the stretching frequency of some specific functional groups. The results obtained from DFT studies clearly indicates the formation of strong intermolecular interaction between 1,3-DAP and AAc.

Evaluating the interaction of human serum albumin (HSA) and 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) liposomes in different aqueous environments using anisotropy resolved multi-dimensional emission spectroscopy (ARMES)

Studying the interaction between plasma proteins and liposomes is critical, particularly for their use as drug delivery systems. Here, the efficacy of anisotropy resolved multidimensional emission spectroscopy (ARMES) for investigating the interaction of human serum albumin (HSA) with liposomes was explored and compared to conventional spectroscopic techniques. Dynamic Light Scattering (DLS) and absorbance spectroscopy (with Multivariate Curve Resolution (MCR) modeling) indicated that the highest degree of liposome rupturing, and aggregation occurred in water, with less in ammonium bicarbonate buffer (ABC) and phosphate buffered saline (PBS). Fluorescence emission spectra of HSA-liposome mixtures revealed significant hypsochromic shifts for water and ABC, but much less in PBS, where the data suggests a non-penetrating protein layer was formed. Average fluorescence lifetimes decreased upon liposome interaction in water (6.2→5.2 ns) and ABC buffer (6.3→5.6 ns) but increased slightly for PBS (5.6→5.8 ns). ARMES using polarized Total Synchronous Fluorescence Scan measurements with parallel factor (PARAFAC) analysis resolved intrinsic HSA fluorescence into two components for interactions in water and ABC buffer, but only one component for PBS. These components, in water and ABC buffer, corresponded to two different HSA populations, one blue-shifted and penetrating the liposomes (λex/em = ~ 280/320 nm) and a second, similar to free HSA in solution (λex/em = ~ 282/356 nm). PARAFAC scores for water and ABC buffer suggested that a large proportion of HSA interacted in an end on configuration. ARMES provides a new way for investigating protein-liposome interactions that exploits the full intrinsic emission space of the protein and thus avoids the use of extrinsic labels. The use of multivariate data analysis provided a comprehensive and structured framework to extract a variety of useful information (resolving different fluorescent species, quantifying their signal contribution, and extracting light scatter signals) all of which can be used to discriminate between interaction mechanisms.