Relative Concentration Profiles Research Articles

A new three-dimensional modeling of fluorescence excitation-emission measurements to explore the interaction of hydroxychloroquine and DNA, and to quantify their binding constant

A new three-dimensional chemometric approach was introduced to explore the interaction of hydroxychloroquine (HCQ)-calf thymus deoxyribonucleic acid (DNA) and quantify binding constant using fluorescence excitation and emission measurements. The fluorescence excitation-emission spectra were recorded after gradual titration of HCQ with DNA. Then, the excitation and emission curves and relative concentrations of the drug and drug-DNA complex were quantitatively estimated using a three-dimensional model called Parallel Factor Analysis (PARAFAC) to a cubic fluorescence data array. The interaction of HCQ and DNA was predicted by applying newly modified Stern-Volmer equations to the relationship between the actual DNA concentration, and the HCQ concentration in the relative concentration profile of the PARAFAC model. In the PARAFAC application, the binding constants of the HCQ-DNA complex at 288, 298, and 310 K were found as 6.78 × 103, 5.07 × 103, and 3.74 × 103 L mol−1, respectively. From the temperature studies, the thermodynamic parameters (ΔS0= 3.528 J mol−1 K−1, ΔH0= −20.099 kJ mol−1 and ΔG0=-21.11, −21.12, and −21.19 kJ mol−1 at 288, 298, and 310 K, respectively) were calculated. The drug-DNA interaction is spontaneous due to negative ΔG0 values. The positive ΔS0 and negative ΔH0 values revealed the major role of the electrostatic force on the binding of HCQ to DNA. Assay results obtained from the proposed three-way modeling were compared to those provided by the traditional spectrofluorimetric method.

Enhancing the emulsification and demulsification efficiency of switchable surfactants through molecular dynamics simulation: The roles of surfactant concentration, salinity, and structure

This study aims to investigate the impacts of a surfactant structure, surfactant concentration, and salt content on switchable emulsification processes through molecular dynamics (MD) simulations. Specifically, we focus on assessing the properties and behaviors of water/tetradecane systems containing CO2-switchable acetamidine surfactant N’-dodecyl-N, N-dimethylacetamidine (C12DMAA) and C18 naphthalene sulfonate (C18PS), both of which are relevant to enhanced oil recovery processes. Utilizing MD simulations, we comprehensively explore the influence of the molecular composition of switchable surfactants, salinity, and surfactant concentration on the reversible processes of emulsification and demulsification in a complex oil/water/C18PS/C12DMAA system. This system can be activated through the injection of CO2 or N2 gas. Various analyses, including molecule mobility, hydration behavior, void volume analysis, a solvent accessible surface area (SASA), a diffusion coefficient, and relative concentration profiles, are employed to gain insights into the emulsification and demulsification processes. Our study reveals that lower surfactant concentrations result in the formation of partial emulsions, while the presence of salt disrupts surfactant hydration and weakens emulsification properties. Additionally, we observe that the impact of hydrogen bonding interactions is less pronounced at lower surfactant concentrations. Furthermore, the MD simulations provided insights into the interplay of a surfactant monomer number and alkyl phenyl introduction with a solvent-accessible surface area (SASA) and a void volume. Understanding these factors is crucial for designing and optimizing emulsion systems, particularly in oil recovery processes. The findings advance our understanding of CO2/N2-switchable surfactants, offering insights into their potential for sustainable development in the petroleum industry. This research contributes to the optimization of switchable surfactants, providing a foundation for improved emulsification processes in enhanced oil recovery applications.

Three-dimensional spectrochromatographic determination of chlorogenic acid in Melampyrum stenophyllum Boiss. extracts by parallel factor analysis.

Co-elution is a common challenge in phytochemical chromatography. Full chromatographic separation often requires extensive optimization, long analysis times, and excessive solvent use. A viable alternative could be mathematical elution of analytes using three-dimensional decomposition. This study aimed to develop a method to determine chlorogenic acid in Melampyrum stenophyllum Boiss. extracts without complete chromatographic separation, to validate the method, and to cross-validate assay results against a classical ultra-performance liquid chromatography (UPLC) method. Ultra-performance liquid chromatography-photodiode array (UPLC-PDA) spectrochromatograms were arranged into a three-way data cube with dimensions of time, wavelength, and sample and then decomposed using parallel factor analysis to reveal chromatographic, spectral, and concentration profiles. The chromatographic and spectral profiles were used to identify chlorogenic acid in overlapping signals. The relative concentration profile was used to quantify it in the plant extract. The assay results were statistically compared with those from an in-house classical UPLC method. Chlorogenic acid was co-eluted at 1.45 min and quantified as 16.11 mg per gram dry weight of Melampyrum stenophyllum extracts (SD = 0.28), despite significant interference in a 4-min runtime. The analytical validity was confirmed by recovery calculations from standard solutions and standard addition samples (RSD < 2%), and the t-test resulted in a p-value of 0.09 (α = 0.05), indicating no significant difference between the results obtained from mathematical elution and chromatographic separation. Chlorogenic acid was quantified from plant material accurately despite the co-elution. Validation and cross-validation results support the method's applicability.

Analyzing moisture diffusion in the interface between rubber-modified asphalt and aggregate: A 3D study considering multiple influencing factors

Moisture erosion is inevitable at the interface between rubber-modified asphalt and aggregate. When moisture penetrates the interface through diffusion, it causes varying degrees of damage. In this study, molecular simulation technology was used to simulate the moisture diffusion interface considering multiple influencing factors. The radial distribution function (RDF), mean square displacement (MSD), and relative concentration profile (RCP) were calculated to evaluate the moisture diffusion direction. Density functional theory was employed to measure the interaction between rubber-modified asphalt components and H2O molecules, and the moisture-damaged areas were analyzed using crystal orbital populations, which can obtain three-dimensional (3D) diffusion mechanism. The results demonstrated that the remaining free H+ ions interacted with the aromatic ring and CC (double bond) in the rubber. Under the effects of multiple factors such as loading and temperature conditions, moisture permeates the rubber-modified asphalt and aggregate interface, resulting in overall degradation of the composition. Furthermore, the hydrogen atoms in the free OH- groups attract the more polar heteroatoms surrounding them.

Molecular dynamics study on the structure and mechanical properties of tobermorite

The calcium silicate hydrate (C-S-H) structure has been indicated its atomic structure in the early stage of hydration resembles the geometry of tobermorite which is a natural calcium silicate hydrate. The mechanical properties of tobermorite crystals were investigated based on molecular dynamics (MD) method in this study. Uniaxial tension simulation in the z-direction was performed to the layered structure of tobermorite 9 Å, 11 Å and 14 Å at molecular level. The stress–strain relationships were obtained, and the structure analysis of tobermorite was carried out in terms of the relative concentration profile and mean square displacement. It has been found that tobermorite 9 Å has the greatest tensile strength compared with tobermorite 11 Å and 14 Å. It also shows that strong interaction between interlayer Ca ions and silicon-oxygen tetrahedra will increase the resistance of tensile loading. These findings may contribute to have a deep knowledge of the intrinsic property of C-S-H.

An Integrated Model Combining Mass Transfer and Chemical Reaction for Co-Decontamination Extraction Step of PUREX Process in a Pulsed Extraction Column

ABSTRACT The accurate prediction of the extraction behaviors of various solutes in PUREX reprocessing process is crucial for the operation and implementation of the actual process. In this paper, an integrated model is developed to predict the extraction behaviors of U, Np, Pu, and HNO3 in the co-decontamination step (1A extraction step) in a pulsed extraction column. The model couples several physical and chemical processes, such as countercurrent flow, mass transfer, and chemical reaction. The mass transfer coefficients and the distribution ratios of U(VI), Pu(IV), Np(IV), Np(V), Np(VI), HNO3 and HNO2 can be obtained using this model. In particular, the redox and disproportion reactions of Np are considered in the model, and the flow direction of Np can be judged under various process conditions and the corresponding influential factors can be analyzed. The judgment is based on the yield calculated from the relative concentration profiles of Np(VI), Np(V), and Np(IV) in the two phases. For neptunium to inter 1AP step, it is necessary to select high nitric acid concentration, low nitrite concentration and especially high flow ratio. For neptunium to inter 1AW step, low nitric acid concentration, high nitrite concentration and low flow ratio are needed. Compared with the experimental data, the relative errors of the distribution ratios of various solutes are less than 30%, and the relative errors of the concentrations of U(VI) and Pu(IV) at the outlet of the organic phase are less than 10%, and our model is indicated to be reliable and applicable for co-decontamination step in the PUREX reprocessing process.

Two-way and three-way resolutions of fluorescence excitation-emission dataset for the co-estimation of two pharmaceuticals in a binary mixture

A new comparative study based on applying two-way and three-way data analysis methods to the fluorescence excitation-emission matrices (EEMs) was performed to co-estimate two active pharmaceutical ingredients (amlodipine besylate, AD, and telmisartan, TS) in a binary mixture. Two-way data analysis was carried out by a bilinear model algorithm using multivariate curve resolution-alternative least squares (MCR-ALS). Three-way data analysis was performed by trilinear models using parallel factor analysis (PARAFAC), and Tucker3. Loadings or profiles obtained by applying the MCR-ALS, PARAFAC, and Tucker3 to the EEMs in the presence of the overlapping excitation and emission spectra made it possible to obtain the individual contribution of the target drugs without requiring a chromatographic separation methodology. The excitation-emission spectra of the analytes were identified from the excitation and emission profiles. The quantity of two pharmaceuticals in analyzed samples was obtained from the relative concentration profiles using univariate calibration. The calibration curves were found to be linear in the range of 0.5–5.0 μg/mL for both drugs. The validity of the methods was verified by analyzing validation samples. Then, the applicability of MCR-ALS, PARAFAC, and Tucker3 approaches was tested for the assay of AD and TS in commercial tablets. For a comparison of the proposed bilinear and trilinear approaches, the statistical analyses including the one-way ANOVA and Bartlett tests were applied to the means and variances of the assay results, respectively. The statistical results showed that the precision and accuracy of the experimental results obtained with the MCR-ALS, PARAFAC, and Tucker3 models were comparable for the assay of the two target drugs.

Visualizing water seepage dynamics in grotto relics via atom-based representative model

Water seepage in grotto relics, i.e., Yungang Grottoes, Dazu Rock Carvings, is a key issue to accurately describe the deterioration and weathering process of grotto rock mass. Considering rainfall infiltration, Finite element simulation was performed for studying the water flow through macro-channel of fractured rock in the 4th cave of Yungang Grottoes, where a group of joints with directions of S62°E and N5°W are widely developed. A 3D atom-based representative model was derived from X-ray diffraction (XRD) patterns and the related semi-quantitative calculation of grotto rock powders, for visualizing the associated seepage characteristics through micro-channel by means of molecular dynamics simulation, for the first time. By analyzing various properties, ranging from the configuration and energetic behaviors to the dynamic characteristics, the calculated water flux and mass flow rate were equal to 270 ns−1 and 8.10 × 10–12 g s−1, respectively. A dynamic process of water transport from the entrance region to the exit region was examined and it is consistent with the relative concentration profiles at the corresponding stage. The tagged O atoms experienced a zigzag movement instead of linear motion as expected, roughly exhibited the same target direction. The seepage characteristics in grotto relics experienced a complex evolution process and three types can be summarized: water infiltrates through micro-channels with a low flow rate; it flows through fracture with a relatively high flow rate; it turned into a kind of analogous pipe flow in inter-connected fracture network, resulting in water seepage hazard. Current simulation studies provide helpful insights for understanding the water flow-infiltration behavior of fractured rock in grotto relics.

Homogeneity Measurements of Li-Ion Battery Cathodes Using Laser-Induced Breakdown Spectroscopy.

We study the capability of nanosecond laser-induced breakdown spectroscopy (ns-LIBS) for depth-resolved concentration measurements of Li-Ion battery cathodes. With our system, which is optimized for quality control applications in the production line, we pursue the goal to unveil manufacturing faults and irregularities during the production process of cathodes as early as possible. Femtosecond laser-induced breakdown spectroscopy (fs-LIBS) is widely considered to be better suited for depth-resolved element analysis. Nevertheless, the small size and intensity of the plasma plume, non-thermal energy distribution in the plasma and high investment costs of fs-LIBS make ns-LIBS more attractive for inline application in the industrial surrounding. The system, presented here for the first time, is able to record quasi-depth-resolved relative concentration profiles for carbon, nickel, manganese, cobalt, lithium and aluminum which are the typical elements used in the binder/conductive additive, the active cathode material and the current collector. LIBS often causes high variations in signal intensity from pulse to pulse, so concentration determination is, in general, conducted on the average of many pulses. We show that the spot-to-spot variations we measure are governed by the microstructure of the cathode foil and are not an expression of the limited precision of the LIBS setup.

Molecular level investigation on the dispersion of hydrophilic modified SiO2 nanoparticles in water from a bond energy viewpoint

AbstractThe dispersion characteristic of nanoparticles is of more interest in some engineering applications, including polymer filling, foam stability, chemical catalysis, and materials surface package. In this paper, the surface modification of SiO2 nanoparticles was carried out based on molecular dynamics simulation. The characteristics of aggregation and diffusion of SiO2 nanoparticles were explained by the radial distribution function (RDF), concentration profile, length distribution, mean squared displacement (MSD), and microscopic testing (MT). The results showed that the orbital provided by the three types of atoms (H, O, and Si) corresponding to the different bandwidths caused the energy alternation of state density. According to the results of RDF, the HO bond energy mainly provided by the water molecules showed the maximum bond energy with 463 kJ/mol. The results indicated that the bonds breakage and formation were accompanied by changes in total energy, kinetic energy, non‐bond energy, and potential energy. After the modification of SiO2 nanoparticles, the concentration profile of the water molecules decreased first at 1–8.5 Å and then increased at 8.5–17.2 Å, but the length distribution climbed to 15.7 at 0.975 Å. When the temperature reached 398 K, the peak value of the length distribution declined to 13.6 Å and the relative concentration profile of water molecules fluctuated around 1.0. With the increase of salinity, the peak value of length distribution reached 15.7 at 0.975 Å, but the concentration profile of water molecules at 3.1–9 Å decreased quickly and then gradually increased. The results of MSD and MT about water molecules presented the largest diffusion coefficient appeared at 398 K and had the best dispersion effect owing to the average kinetic energy among the molecules. Conversely, the diffusion coefficient decreased with the incremental solution salinity because the inhabitation of sodium for the motion of water molecules resulted in the ion bridging and hydrogen bonding.

Comparing Direct Numerical Modeling Predictions With Field Evidence for Methane Vertical Microseepage in Two Geological Settings

The footprints of petroleum microseepage can be associated with chemical and microbial processes in initially homogeneous strata and/or with the fluid transport properties of the rocks through which oil and gas migrate. This work examines the role of such driving factors in two contrasting geological settings by comparing numerical modeling predictions for upward methane microseepage with some field evidence for hydrocarbons transport and accumulation. The two case studies are a monitoring borehole (BH8) from a landfill in southern Ontario, Canada, and an oil well (Saltarin 1A) from the Eastern Llanos Basin in Colombia. Profiles of relative methane concentrations versus depth were generated using a time-dependent, one-dimensional, simulation of the advection-diffusion equation applied to multiple strata of soils, and sediments. The model employs the layered sequences of these two geological settings. The results obtained hinge on the standard permeability values for the rock types involved and their corresponding flow velocities and diffusion coefficients. Resistivity logs were utilized as direct proxies of hydrocarbon concentrations. As additional evidence for petroleum microseepage, experiments of electron paramagnetic resonance (EPR) were carried out in drilling cuts of Saltarin 1A to measure traces of organic matter free radicals concentrations (OMFRC). Extractable organic matter (EOM) and magnetic susceptibility data were also considered in interpreting the EPR results. Qualitative comparisons between modeled methane profiles and their corresponding resistivity logs suggest that microseepage and hydrocarbon accumulations are conditioned by the fluid transport properties of the rocks contained by BH8 and Saltarin 1A. Moreover, in most of the Saltarin 1A sequence, the OMFRC profiles follow the trends displayed by the resistivity and modeled methane logs. Thus, the EPR data also indicates that hydrocarbon microseepage and accumulation are largely controlled by lithology. Conversely, EOM and magnetic susceptibility appear to be evidence for hydrocarbon-mediated near-surface chemical processes.

Sorption of Per- and Polyfluoroalkyl Substances (PFAS) using Polyethylene (PE) microplastics as adsorbent: Grand Canonical Monte Carlo and Molecular Dynamics (GCMC-MD) studies

ABSTRACT Per- and Polyfluoroalkyl Substances (PFAS) and microplastics (MPs) removal is one of the main technical measures in these emerging pollutant control and MPs can sorb PFAS acting as carriers. In order to explore the sorption process of polyethylene (PE MPs) for different PFAS, Grand Canonical Monte Carlo and molecular dynamics simulation was used. Seven commonly found PFAS compounds including PFNA (Perfluorononanoic acid), PFHxS (Perfluorohexanesulphonic acid), PFHxA (Perfluorohexanoic acid), PFDA (Perfluorodecanoic acid), PFOS (Perfluorooctanesulfonic acid), PFBS (Perfluorobutanesulfonic acid) and Perfluorooctanoic acid (PFOA) were selected. The sorption on PE MPs was based on fixed loading and the sorption (PE MPs+PFAS) average total energy for all simulation steps followed PFHxA (−29.17 kcal/mol) < PFBS (−52.71 kcal/mol) < PFOA (−57.12 kcal/mol) < PFNA (−70.58 kcal/mol) < PFDA (−78.27 kcal/mol) < PFHxS (−80.06 kcal/mol) < PFOS (−102.30 kcal/mol). However, the binding/interaction energies followed PFHxS > PFOS > PFNA > PFDA > PFOA > PFBS > PFHxA. The MD simulation was carried out under NVT ensemble at 298 K, the thermodynamic states and relaxation pretreatment procedures were then examined quantitatively by radial distribution function, X-ray scattering, relative concentration profile, mean square displacement and space time correlation function. The results show that effective sorption of PFAS molecule by PE MPs involves hydrogen or chemical bonding as well non-bond energy such as Van der Waals (VdW), electrostatic and intramolecular energies. The cell volume did not change during single and multicomponent sorption while the sorption density increased about threefold the single component (0.36 g/cm3), suggesting that as the pollutant number increased the sorption capacity increased. This study showed that PE MPs can used for single and multicomponent sorption of PFASs effectively and also provided theoretical support for our knowledge of the sorption mechanism at the molecular level, which will help in better understanding of PFAS removal by MPs.

Atomic Scale Investigation on the Structural and Mechanical Properties of Carbon Nanotubes Reinforced Polylactic acid Composites

AbstractMolecular characterization of nanocomposites is of great significance for the design, prediction, and understanding of the structure and properties of nanocomposites. Herein, a molecular dynamics simulation method is employed to investigate the structures, thermodynamical, and mechanical properties of carbon nanotubes (CNTs) reinforced polylactic acid (PLA) composites, as well as the effects and mechanisms of CNTs on the structure and mechanical properties of PLA matrices. The concentration profile result suggests that the type of CNTs has a significant influence on the distribution of PLA molecular chains, with relative concentration profiles around CNTs in the order of PLA/CNTs‐COOH &gt; PLA/CNTs‐OH &gt; PLA/CNTs‐NH2 &gt; PLA/CNTs. Incorporating CNTs into the PLA matrix decreases the FFV and mobility of the polymer, where the trend is PLA &gt; PLA/CNTs &gt; PLA/CNTs‐NH2 &gt; PLA/CNTs‐OH &gt; PLA/CNTs‐COOH. Meanwhile, the tensile properties of the PLA matrix increase with the incorporation of CNTs, and the trend agrees with the results of fractional free volume (FFV) and relative concentration distribution. Finally, the analysis results of interaction illustrate that hydrogen bond interactions between PLA molecular chains and the functional groups on CNTs surface are involved in the adsorption of the polymers on the CNTs surface, thus affecting their interfacial interaction, structure, and properties.

Planar laser-induced fluorescence measurement of the angular pattern of the cone-shaped spray

In the present work, a PLIF-based approach for a large cone-shaped spray patternation ispresented and experimental results of its application are discussed. The patternation approach is based on simple time-averaged PLIF imaging. Special attention is paid to the image and data processing in order to simplify a patternation results interpretation. Experimental testing was performed on a water spray, formed by centrifugal nozzle at atmospheric ambient pressure. Circumferential relative concentration profiles in spray crosswise plane are presented in the paper and their validity is analysed.

A novel strategy on the spectrochromatographic analysis of a quaternary mixture by parallel factor analysis model.

Poor chromatographic resolution is one of the main challenges in chromatographic analysis. Partially separated chromatographic peaks frequently occur, due to the nature of analytes and the demand for fast analysis using high flow rates and shorter columns. Modeling of chromatographic three-way data using suitable chemometric tools enables determining co-eluted peaks without using additional experimental efforts. In this paper, parallel factor analysis (PARAFAC) was applied to chromatographic data for the quantitative resolution of a quaternary mixture at the co-elution condition of acetaminophen, aspirin, ascorbic acid, and guaifenesin in a spectrochromatogram. The spectrochromatograms of the calibration set, validation set, and real samples were arranged as a three-way array. In the next step, the PARAFAC model was implemented to decompose the spectrochromatographic array into trilinear components, corresponding to spectral, chromatographic, and relative concentration profiles of the analytes. The chromatographic and spectral modes were used for the qualitative analysis of components, whereas the analytes in commercial tablets were quantified from their individual profiles in their concentration mode. This study indicated that the application of the PARAFAC model provided a novel strategy for determining overlapping peaks in a chromatogram to perform the analysis of multicomponent mixtures with reduced runtime and without additional efforts.

Microscopic adsorption behaviors of ionic surfactants on lignite surface and its effect on the wettability of lignite: A simulation and experimental study

In this study, the microscopic adsorption behaviors of two ionic surfactants, sodium dodecyl sulfonate (SDS) and dodecyltrimethylammonium bromide (DTAB), on the lignite surface were investigated at the molecular level through molecular dynamics simulations. A series of properties of surfactant–lignite adsorption systems, including relative concentration profiles, radial distribution functions, surface areas (surface roughness), mean square displacements, and interaction energies were calculated to illustrate the microscopic adsorption behaviors in detail. Analysis of the equilibrated interfacial properties indicated that the adsorption of SDS on the lignite surface is dominated by van der Waals force and can decrease the surface area (roughness) of lignite. In addition, there is no preferential orientation for SDS adsorption on lignite surface. However, driven by electrostatic attraction, the head group of DTAB can be strongly adsorbed on the lignite surface. Furthermore, it was also found that the effect of surfactant adsorption on the surface wettability of lignite showed the same trends as the adsorption strength. The change in the wettability of lignite resulting from surfactant adsorption was discussed in depth, and the explanations were given based on the charge characteristics of head group of surfactant and adsorption orientation. The simulation evaluations of the adsorption behaviors and wettability alteration of lignite surface caused by these two ionic surfactants agreed well with the existing experimental data. This investigation present here visualized the microscopic characteristics of surfactant adsorption and facilitated a better understanding about the involved mechanism.

Analytical model for the suspended sediment concentration in the ice-covered alluvial channels

Ice cover formed on an alluvial channel can significantly alter the flow characteristics, such as the vertical distributions of streamwise velocity and shear stress, and hence the water and sediment transport process. The vertical profile of the suspended sediment concentration in the ice-covered alluvial channels with steady uniform flows is investigated in this study. To calculate the suspended sediment concentration, we are based on the Schmidt O’Brien equation and deduce an analytical model that employs an existing eddy viscosity model and a modified formula of the sediment fall velocity considering the common effects of the upper and lower boundaries. The proposed analytical model is then validated by using available experimental data reported in the literature. The predicted accuracy of the proposed model is evaluated through error statistics by comparing to previous modeled results. The relative concentration profiles of the suspended sediment are subsequently simulated by applying the validated analytical model with different characteristic parameters. Results show that the relative concentration decreases with the increase of both the ice cover roughness and the sediment fall velocity. The uniformity of the relative concentration distribution is closely related to the value of the proportionality parameter σ, revealing the physical mechanism that the more prominent the turbulent diffusion effect is, the more uniform the relative concentration profile is.

Influence of the sampling probe on flame temperature, species, residence times and on the interpretation of ion signals of methane/oxygen flames in molecular beam mass spectrometry measurements

Laminar flames are widely used to analyze the fundamentals of combustion processes using molecular beam mass spectrometry. The extraction of a representative sample from a flame by an intrusive sampling technique is challenging because of two main issues. First, the sampling probe itself perturbs the flow and temperature field, affecting the species profiles. These effects need to be characterized by 2-D fluid dynamic simulations to reveal sources of perturbations that are in particular suction and flame cooling. Second, some intermediate species interact with the sampling probe and are removed from the gas sample before analysis. The concentrations of these intermediates in the flames are often low and close to the detection limit. Naturally occurring ions can also be extracted from the flame by molecular beam sampling. Coupled with modern ion optical devices for ion transfer to the mass analyzer very high sensitivity can be reached in the detection of ionic species in flames. Similarities in the shape of measured relative concentration profiles indicate a connection between neutrals and the corresponding protonated molecules by proton transfer reactions. A quantification method of neutral flame species based on signals of the flame-sampled ions is presented and evaluated for the intermediate methanol in methane/oxygen/argon flames. The proposed method is based on equilibrium calculations that depend on temperature. To characterize the sampling process and demonstrate the validity of the quantification approach for ion measurements, the influence of the sampling probe on flame temperature and mole fraction profiles of the main species and the intermediate methanol are investigated by a combined experimental and simulation study. A comparison of the methanol profiles measured by conventional molecular beam sampling and the novel ion sampling technique reveal acceptable agreement. This work shows that if all aspects of sampling are considered as well as possible, the ion sampling technique allows access to kinetic data of neutral intermediates.

Three-Way Analysis-Based pH-UV-Vis Spectroscopy for Quantifying Allura Red in An Energy Drink and Determining Colorant's pKa

Three-way analysis-based pH-UV-Vis spectroscopy was proposed for quantifying allura red in an energy drink product without the need for chromatographic analysis, and determining the colorant’s pKa without using any titration technique. In this study, UV-Vis spectroscopic data matrices were obtained from absorbance measurements at five different pH levels from pH 8 to pH 12 and arranged as a three-way array (wavelength × sample × pH). In the three-way analysis procedure, parallel factor analysis (PARAFAC) was implemented to decompose the three-way array into a set of trilinear components. Each set of three components relates to spectral, pH and relative concentration profiles of allura red and sample matrix in the energy drink. First, UV-Vis spectra of the colorant’s acid-base pair and sample’s matrix were characterized by using the estimated spectral profile. Then, from the pH profile the pKa value was found to be 11.28 for the related colorant. Finally, allura red in energy drink samples was determined using the estimated concentration curve in the relative concentration profile. In the quantitation procedure, the working concentration range was 0.8–19.2 μg/mL. PARAFAC approach was tested in terms of selectivity, precision, and accuracy of the method. Added recovery results obtained by applying the proposed method to spiked samples were between 101.5% and 103.5%. In the application of the method to the analysis of real samples, successful results were reported. For a comparison, an ultra-performance liquid chromatographic method was developed for the quantitation of the colorant. Compared to the chromatographic method, we observed that PARAFAC model was simple and less expensive without requiring separation.

Novel Three-Dimensional Resolution of a pH and Ultraviolet-Visible Absorption Spectral Dataset for the Determination of Desloratadine in a Pharmaceutical Product and Its Acid Dissociation Constant

Three-way data analysis (or multi-way data analysis) of higher-order records is required to develop new and potential resolution methods to reveal multiple latent information or hidden features from multicomponent systems in presence of unknown interferences. This article presents a new application of parallel factor analysis (PARAFAC), which is one of the multiway analysis techniques, to quantify desloratadine in sirup and to simultaneously determine its acid dissociation constant (pKa) in the presence of spectral interferences without using complex and expensive instrumental methods. The three-dimensional pH-absorbance dataset, which was obtained as a function of wavelength, pH and concentration, was decomposed using the PARAFAC algorithm to obtain the estimated spectral, pH and relative concentration profiles of acid-base pair of desloratadine and sirup excipients. The quantity of the drug in sirup formulation was calculated from the estimated relative concentration profile, which was one of the three modes. At the same time, the acid dissociation constant of desloratadine was determined using the estimated pH profile of the acid and base species in their equilibrium. The applicability of the PARAFAC method was confirmed by the analysis of validation samples. In the practical application of the PARAFAC method to real samples, successful results were reported for the quality control of a sirup formulation containing desloratadine and for the estimation of desloratadine’s pKa value. The PARAFAC assay results were compared to results obtained by ultra-performance liquid chromatography (UPLC).