Gas Matrices Research Articles

Numerical simulation study of coal seam dual-porosity medium fluid-solid coupling model and directional long borehole gas drainage

To accurately reflect the gas migration law during coal seam gas drainage, this study established a coal seam dual-porosity medium fluid-solid coupling model that takes into account the influence of matrix gas diffusion, fracture gas seepage, Klinkenberg effect and tortuosity. A three-dimensional numerical simulation of directional long boreholes gas drainage in coal seams was then performed using COMSOL simulation software and the accuracy of the model was verified by field test results. The research results showed that the maximum error between the effective drainage radius of directional long boreholes obtained from numerical simulation and the field test results is 6.0%, which validates the accuracy of the constructed dual-porosity medium fluid-solid coupling model in coal seams. In addition, this paper compared and analyzed the effective drainage radius of long boreholes and coal seam permeability obtained by numerical simulation under different influencing factors, and found that the effective drainage radius and permeability without considering Klinkenberg effect and fracture gas seepage are relatively small, while the effective drainage radius and permeability without considering tortuosity and matrix gas diffusion are relatively large. This indicated that Klinkenberg effect and fracture gas seepage promote coal seam gas flow, while tortuosity and matrix gas diffusion inhibit it.

Isolation and characterization of a two-coordinate phosphinidene oxide.

Nitroso compounds, R-N=O, are common intermediates in organic synthesis, and are typically amenable to storage and manipulation at ambient temperature under aerobic conditions. By contrast, phosphorus-containing analogues, such as R-P=O (R = OH, CH3, OCH3, Ph), are extremely reactive and need to be studied in inert gas matrices at ultralow temperatures (3-15 K). These species are believed to be key intermediates in the degradation/combustion of organic phosphorus compounds, a class of chemicals that includes chemical warfare agents and flame retardants. Here we describe the isolation of a two-coordinate phosphorus(III) oxide under ambient conditions, enabled by the use of an extremely bulky amine ligand. Reactivity studies reveal that the phosphorus centre can be readily oxidized, and that in doing so, the P-O bond remains intact, an observation that is of interest to the proposed reactivity of transient phosphorus(III) oxides.

Highly selective and sensitive detection of volatile organic compounds using long wavelength InAs-based quantum cascade lasers through quartz-enhanced photoacoustic spectroscopy

The precise detection of volatile organic compounds plays a pivotal role in addressing environmental concerns, industrial safety, and medical diagnostics. The accurate identification and quantification of these compounds because of their ubiquity and potential health hazards has fueled the development of advanced sensing technologies. This work presents a sensing system in the realm of long-wavelength infrared spectroscopy for achieving enhanced selectivity and sensitivity of benzene, toluene, and propane detection through quartz-enhanced photoacoustic spectroscopy. High-resolution gas spectroscopy is made possible by the use of specially designed InAs/AlSb-based quantum cascade lasers, emitting in the wavelength range 13–15 μm, and quartz tuning forks. The sensor system, characterized by its robustness and precision, demonstrates exceptional capabilities in benzene, toluene, and propane detection. The system's capacity for practical applications in environmental monitoring and medical diagnostics is demonstrated by its ability to distinguish these volatile organic compounds with a minimum detection limit of 113 ppb, 3 ppb, and 3 ppm for toluene, benzene, and propane at an integration time of 10 s, even in complex gas matrices. This work advances gas sensing technology while also offering insightful information on spectral interferences, a persistent problem in the field. The results usher in a new era of sophisticated and reliable gas sensing techniques meeting the growing demand for precise volatile organic compounds detectors for environmental monitoring purposes.

Deep-Ultraviolet Photoexcitation of Aqueous Urea Forms Carbamic Acid/Carbamate in Less Than One Picosecond.

Urea is believed to have been essential to the synthesis of prebiotic nucleotides and thereby the RNA or DNA of the first lifeforms. Models suggesting that life began in wet-dry cycles around shallow aquatic ponds imply that reactants such as urea were exposed to deep ultraviolet irradiation from the young sun. Detrimental photodissociation of urea induced by deep UV excitation potentially challenges these models. We here follow the primary deep ultraviolet photochemistry of aqueous urea. The data show that urea is barely excited at 200 nm due to weak ultraviolet absorption. The likelihood of photodissociation is further reduced by strong intra-molecular coupling of the CN and CO stretch vibrations accompanied by an efficient dissipation of the excitation energy to the surrounding water molecules mitigated by urea-water hydrogen bonds. We find that 54±5 % of the excited urea molecules dissociate. Reactions between the photoproducts and surrounding solvent molecules form carbamic acid or the carbamate anions within 0.6 ps. The molecules that do not dissociate return to the electronic ground state in 2 ps. Interestingly, the photodissociation processes of urea in the aqueous phase is different from earlier reported reactions observed following the VUV photolysis of urea in noble gas matrices and highlight the potential influence of water on the prebiotic photochemistry.

Adsorption efficacy of acetone with zeolitic imidazolate frameworks–8: a mechanistic and kinetic insight

ABSTRACT The zeolitic imidazolate framework-8 (ZIF-8) has been investigated for the dynamic adsorption of acetone from the gas phase. In this study, ZIF-8 was synthesised using a cost-effective and environmentally friendly method and characterised using SEM, XRD, BET, and FTIR. The synthesised ZIF-8 possessed a BET surface area of 1212 m2. g−1 and a 0.64 µm particle size. The dynamic adsorption efficacy of acetone on the thermally pretreated ZIF-8 was investigated in a gas matrix under different operational factors. Increasing the acetone concentration through the adsorbate inlet from 300 to 800 ppm enhanced the adsorption capacity from 114 to 162 mg. g−1, while increasing flow rates from 100 to 200 mL. min−1 diminished the adsorption capacity from 120 to 114 mg. g−1. Additionally, increasing the relative humidity from 30 to 70% diminished the adsorption capacity from 130 to 87 mg. g−1. The acetone adsorption kinetics on ZIF-8 were investigated by the Elovich equation, pseudo-first order (PFO), and pseudo-second order (PSO) models. The statistical parameters indicated that the Elovich equation model is most suitable for representing the kinetic behaviour. In conclusion, ZIF-8 could be introduced as a sorbent with suitable potential for adsorbing acetone from the air in various environmental and occupational settings.

Mechanistic analysis of acid gas storage and oil recovery in naturally fractured reservoirs using single matrix block approach

AbstractThe objective of this study is to assess the storage of acid gas, containing CO2 and H2S, in a depleted naturally fractured reservoir (NFR) using single matrix block (SMB) approach. The acid gas dissolution in oil is considered by Peng‐Robinson equation of state and compositional simulation. The PHREEQC package is used to determine acid gas solubility in formation brine. Three types of acid gases with different compositions are used for this study and their swelling behavior and miscibility in relation to the reservoir oil are analyzed. An SMB model, with a matrix block surrounded by fractures, is constructed, and validated for simulation of a real experiment. The simulation is conducted for synthetic and real reservoir fluids when the oil is in its residual saturation. A sensitivity analysis is performed to study the effects of key parameters, such as acid gas composition, reservoir pressure, permeability, porosity and matrix height on the storage capacity and oil recovery factor. The matrix has a volume of 27 m3 and about half of acid gas storage is achieved in the first 5 years while the simulations are run for 30 years. The results show that up to 90% of remained oil is recoverable, and more than 0.67 kmol of acid gas per cubic meter of matrix is stored whether matrix contains a real oil or a synthetic one. Higher storage is achieved for higher matrix porosities and heights and large H2S proportion in acid gas. In all cases about 10% of acid gas is trapped in water and the remaining 90% is dissolved in oil. The mineral trapping was more active in CO2‐rich acid gases. While about 10 kg of the matrix rock was dissolved in the acidic brine when the acid gas contained H2S, the amount of the dissolved minerals in acidic brine resulted from the injection of CO2‐rich acid gas was more than 16 kg. Finally, this study gives a comparative analysis of the storage performance of acid gas mixture and pure CO2. © 2024 Society of Chemical Industry and John Wiley & Sons, Ltd.

Probing the electronic structure and ground state symmetry of gas phase C60+ via VUV photoionization and comparison with theory.

Recently, some of us reviewed and studied the photoionization dynamics of C60 that are of great interest to the astrochemical community as four of the diffuse interstellar bands (DIBs) have been assigned to electronic transitions in the C60+ cation. Our previous analysis of the threshold photoelectron spectrum (TPES) of C60 [Hrodmarsson et al., Phys. Chem. Chem. Phys. 22, 13880-13892 (2020)] appeared to give indication of D3d ground state symmetry, in contrast to theoretical predictions of D5d symmetry. Here, we revisit our original measurements taking account of a previous theoretical spectrum presented in the work of Manini et al., Phys. Rev. Lett. 91(19), 196402 (2003), obtained within a vibronic model parametrized on density functional theory/local-density approximation electronic structure involving all hg Jahn-Teller active modes, which couple to the 2Hu components of the ground state of the C60+ cation. By reanalyzing our measured TPES of the ground state of the C60 Buckminsterfullerene, we find a striking resemblance to the theoretical spectrum calculated in the work of Manini et al., Phys. Rev. Lett. 91(19), 196402 (2003), and we provide assignments for many of the hg modes. In order to obtain deeper insights into the temperature effects and possible anharmonicity effects, we provide complementary modeling of the photoelectron spectrum via classical molecular dynamics (MD) involving density functional based tight binding (DFTB) computations of the electronic structure for both C60 and C60+. The validity of the DFTB modeling is first checked vs the IR spectra of both species which are well established from IR spectroscopic studies. To aid the interpretation of our measured TPES and the comparisons to the abinitio spectrum we showcase the complementarity of utilizing MD calculations to predict the PES evolution at high temperatures expected in our experiment. The comparison with the theoretical spectrum presented in the work of Manini et al., Phys. Rev. Lett. 91(19), 196402 (2003), furthermore, provides further evidence for a D5d symmetric ground state of the C60+ cation in the gas phase, in complement to IR spectroscopy in frozen noble gas matrices. This not only allows us to assign the first adiabatic ionization transition and thus determine the ionization energy of C60 with greater accuracy than has been achieved at 7.598 ± 0.005eV, but we also assign the two lowest excited states (2E1u and 2E2u) which are visible in our TPES. Finally, we discuss the energetics of additional DIBs that could be assigned to C60+ in the future.

Which molecules can challenge density-functional tight-binding methods in evaluating the energies of conformers? investigation with machine-learning toolset

Large organic molecules and biomolecules can adopt multiple conformations, with the occurrences determined by their relative energies. Identifying the energetically most favorable conformations is crucial, especially when interpreting spectroscopic experiments conducted under cryogenic conditions. When the effects of irregular surrounding medium, such as noble gas matrices, on the vibrational properties of molecules become important, semi-empirical (SE) quantum-chemical methods are often employed for computational simulations. Although SE methods are computationally more efficient than first-principle quantum-chemical methods, they can be inaccurate in determining the energies of conformers in some molecules while displaying good accuracy in others. In this study, we employ a combination of advanced machine learning techniques, such as graph neural networks, to identify molecules with the highest errors in the relative energies of conformers computed by the semi-empirical tight-binding method GFN1-xTB. The performance of three different machine learning models is assessed by comparing their predicted errors with the actual errors in conformer energies obtained via the GFN1-xTB method. We further applied the ensemble machine-learning model to a larger collection of molecules from the ChEMBL database and identified a set of molecules as being challenging for the GFN1-xTB method. These molecules hold potential for further improvement of the GFN1-xTB method, showcasing the capability of machine learning models in identifying molecules that can challenge its physical model.

Highly efficient reduction of bromate by vacuum UV/sulfite system

Bromate (BrO3-), a worldwide regulated by-product after ozone disinfection, is often detected in bromide-containing water, and has a strict limit of 10 μg L−1 in potable water. BrO3- degradation by advanced reduction processes (ARPs) has gained much attention because of efficient removal and easy integration with ultraviolet disinfection (UV at 254 nm). In the vacuum UV (VUV, 185/254 nm)/sulfite system, the elimination kinetics of BrO3− increased by 9-fold and 15-fold comparing with VUV alone and UV/sulfite system. This study further demonstrated the hydrated electron (eaq-) works as the dominant species in BrO3- degradation in alkaline solution, while in the acidic solution the H• became a secondary reactive species besides eaq−. Hence, the influences of pH, sulfite concentration, dissolved gas and water matrix on effectiveness of degradation kinetics of BrO3- was explored in details. With increasing pH, the proportion of SO32− species increased and even became the major ones, which also correlated well with the kobs (min−1) of BrO3− degradation. The stability of eaq− also climbs with increasing pH, while that of H• drops significantly. Higher sulfite dosage favored a more rapid degradation of BrO3−. The presence of dissolved oxygen inhibited BrO3- removal due to the scavenging effect of O2 toward eaq− and transformed VUV/sulfite-based ARP to an advanced oxidation process (AOP), which was ineffective for BrO3- removal. BrO3- removal was inhibited to varying degrees after anions (e.g., bicarbonate (HCO3−), chloride (Cl−), nitrate (NO3−)) and humic acid (HA) being added.

Rotating disk diluter hyphenated with single particle ICP-MS as an online dilution and sampling platform for metallic nanoparticles characterization in ambient aerosol

The application of single particle inductively coupled plasma mass spectrometry (spICP-MS) for online metallic nanoparticles (NPs) characterization in ambient aerosol remains a challenge. In this study, a hyphenated setup consisting of a rotating disk diluter (RDD) with spICP-MS (RDD-spICP-MS) was used for online sampling and characterization NPs in ambient pressure aerosols. The elemental composition, particle size distribution, and particle number concentration (PNC) of metallic NPs in aerosols could be obtained simultaneously. The RDD allowed sampling of the aerosol at a constant flow rate, adjusting the optimal dilution ratio for characterizing NPs at different PNCs, and exchanging the gas matrix to achieve the requirement of spICP-MS for direct aerosol characterization. In this proof-of-concept study, the feasibility of this setup was tested with AuNPs of different sizes from the argon-based and air-based aerosol. The limit of detection for number concentration is below 30 #/L, which is lower than the regulated environmental level. Moreover, multi-modal samples, as well as the interference of ionic species, were accurately investigated. Finally, AuNPs were spiked with environmental PM10 and Road dust to evaluate the matrix effect as well as the capabilities of the setup to characterize environmental aerosol samples. These results indicate that RDD-spICP-MS has a great potential for online characterization of metallic NPs in the ambient aerosol.

Multivariate analysis and digital twin modelling: Alternative approaches to evaluate molecular relaxation in photoacoustic spectroscopy

A comparative analysis of two different approaches developed to deal with molecular relaxation in photoacoustic spectroscopy is here reported. The first method employs a statistical analysis based on partial least squares regression, while the second method relies on the development of a digital twin of the photoacoustic sensor based on the theoretical modelling of the occurring relaxations. Methane detection within a gas matrix of synthetic air with variable humidity level is selected as case study. An interband cascade laser emitting at 3.345 µm is used to target methane absorption features. Two methane concentration ranges are explored targeting different absorptions, one in the order of part-per-million and one in the order of percent, while water vapor absolute concentration was varied from 0.3 % up to 2 %. The results achieved employing the detection techniques demonstrated the possibility to efficiently retrieve the target gas concentrations with accuracy > 95 % even in the case of strong influence of relaxation effects.

Light-induced thermoelastic sensor for ppb-level H2S detection in a SF6 gas matrices exploiting a mini-multi-pass cell and quartz tuning fork photodetector

We present an optical sensor based on light-induced thermoelastic spectroscopy for the detection of hydrogen sulfide (H2S) in sulfur hexafluoride (SF6). The sensor incorporates a compact multi-pass cell measuring 6 cm × 4 cm × 4 cm and utilizes a quartz tuning fork (QTF) photodetector. A 1.58 µm near-infrared distributed feedback (DFB) laser with an optical power of 30 mW serves as the excitation source. The sensor achieved a minimum detection limit (MDL) of ∼300 ppb at an integration time of 300 ms, corresponding to a normalized noise equivalent absorption coefficient (NNEA) of 3.96 × 10−9 W·cm−1·Hz−1/2. By extending the integration time to 100 s, the MDL can be reduced to ∼25 ppb. The sensor exhibits a response time of ∼1 min for a gas flow rate of 70 sccm.

Relating the microstructural and glass transition temperature evolution of a carbon–carbon composite precursor during pyrolysis using thermomechanical analysis

AbstractPolybenzoxazine thermoset resins exhibit significant potential as precursors for carbon–carbon composites, owing to their high char yield upon pyrolysis. During pyrolysis, the resin is converted to an amorphous carbon‐rich material through a series of mechanisms, resulting in a linear increase of the glass transition temperature (TG) from 133 to 396°C at 0.48 pyrolytic conversion. To better understand this relationship, a non‐isothermal kinetic model was integrated, enabling the prediction of the TG onset, inflection, and endpoint based on the heat treatment protocol (process temperature (TP) vs. time) and the total volume of pyrolytic gases generated. By considering the TG behavior and anticipated gas effects, three distinct mechanisms were identified: (1) gas accumulation and matrix expansion leading to increased sample thickness (TG < TP), (2) crack network formation caused by gas‐pressure‐induced brittle failure (TG > TP), and (3) sample thickness reduction due to gas venting through the crack network (TG < TP). To validate this theory, thermal mechanical analysis was performed during pyrolysis, and changes in thickness (±ΔL/L0) were attributed to gas pressure‐related matrix deformation. Conversely, no change in ΔL/L0 indicated the formation of an interconnected crack network through which gases could vent without building a measurable internal pressure.

Vibrationally resolved electronic spectroscopy of rhodamine B cation at less than 5 K: combining gas phase absorption and matrix isolation fluorescence spectroscopy

Helium tagging photodissociation action spectroscopy in the gas phase together with laser-induced fluorescence (LIF) spectroscopy in neon matrix has been used to probe the photophysics of electrosprayed rhodamine B cation cooled to < 5 K and studied in two different minimally perturbing environments ([RhB•He]+ as well as [RhB]+ in solid neon). Helium tagging experiments were performed using a newly developed apparatus He-TAG. LIF measurements were carried out using an improved matrix-isolation spectroscopy machine Depo-II. The resulting, partially vibrationally resolved electronic spectra of the S0→S1, resp. S1→S0 transition provide benchmarks for gauging the theoretical description of this prototypical organic dye. As a first approach, we have compared our spectra to TD-DFT-based predictions of vibronic structure at the Franck-Condon (FC) and Franck-Condon Herzberg-Teller (FCHT) levels. Depletion action and fluorescence spectroscopy of rhodamine B cation at < 5 K

Infrared Spectroscopic Studies of Oxygen Atom Quantum Diffusion in Solid Parahydrogen.

The thermally induced diffusion of atomic species in noble gas matrices was studied extensively in the 1990s to investigate low-temperature solid-state reactions and to synthesize reactive intermediates. In contrast, much less is known about the diffusion of atomic species in quantum solids such as solid parahydrogen (p-H2). While hydrogen atoms were shown to diffuse in normal-hydrogen solids at 4.2 K as early as 1989, the diffusion of other atomic species in solid p-H2 has not been reported in the literature. The in situ photogeneration of atomic oxygen, by ArF laser irradiation of an O2-doped p-H2 solid at 193 nm, is studied here to investigate the diffusion of O(3P) atoms in a quantum solid. The O(3P) atom mobility is detected by measuring the kinetics of the O(3P) + O2 → O3 reaction after photolysis via infrared spectroscopy of the O3 reaction product. This reaction is barrierless and is thus assumed to be diffusion-controlled under these conditions such that the reaction rate constant can be used to estimate the oxygen atom diffusion coefficient. The O3 growth curves are well fit by single exponential expressions allowing the pseudo-first-order rate constant for the O(3P) + O2 → O3 reaction to be extracted. The reaction rates are affected strongly by the p-H2 crystal morphology and display a non-Arrhenius-type temperature dependence consistent with quantum diffusion of the O(3P) atom. The experimental results are compared to H(2S) atom reaction studies in p-H2, analogous studies in noble gas matrices, and laboratory studies of atomic diffusion in astronomical ices and surfaces.

Trace photoacoustic SO2 gas sensor in SF6 utilizing a 266 nm UV laser and an acousto-optic power stabilizer.

A sulfur dioxide (SO2) gas sensor based on the photoacoustic spectroscopy technology in a sulfur hexafluoride (SF6) gas matrix was demonstrated for SF6 decomposition components monitoring in the power system. A passive Q-switching laser diode (LD) pumped all-solid-state 266 nm deep-ultraviolet laser was exploited as the laser excitation source. The photoacoustic signal amplitude is linear related to the incident optical power, whereas, a random laser power jitter is inevitable since the immature laser manufacturing technology in UV spectral region. A compact laser power stabilization system was developed for better sensor performance by adopting a photodetector, a custom-made internal closed-loop feedback controller and a Bragg acousto-optic modulator (AOM). The out-power stability of 0.04% was achieved even though the original power stability was 0.41% for ∼ 2 hours. A differential two-resonator photoacoustic cell (PAC) was designed for weak photoacoustic signal detection. The special physical constants of SF6 buffer gas induced a high-Q factor of 85. A detection limit of 140 ppbv was obtained after the optimization, which corresponds to a normalized noise equivalent absorption coefficient of 3.2 × 10-9 cm-1WHz-1/2.

Rapid Detection of Volatile Organic Compounds by Switch-Scan Tuning of Vernier Quantum-Cascade Lasers.

Volatile organic compounds (VOCs) exhibit typically broad and mutually overlapping ro-vibrational absorption fingerprints. This complexity has so far limited the applicability of laser-based spectroscopy for VOC measurements in complex gas matrices. Here, we exploit a Vernier-type quantum-cascade laser (QCL) as an electrically tunable multiwavelength source for selective and sensitive VOC analysis. This emerging class of lasers provides access to several spectral windows by discrete Vernier tuning ("switching") and continuous coverage within these windows ("scanning"). We present a versatile driving technique that efficiently combines the two tuning mechanisms. Applied to our Vernier QCL, it enables the rapid acquisition (within 360 ms) of high-resolution spectra from six individual spectral windows, distributed over a wide range from 1063 to 1102 cm-1. Gaining access to the broad absorption envelopes of VOCs at multiple frequencies, along with their superimposed fine structure, which are especially pronounced at a reduced sample pressure, offers completely new opportunities in VOC analysis. The potential of this approach is assessed in a direct-laser-absorption setup with acetaldehyde, ethanol, and methanol as benchmark compounds with significant spectral overlaps. A measurement precision of 1-10 ppb is obtained after integration for 10 s at amount fractions below 10 ppm, and excellent linearity is found over at least 3 orders of magnitude. Combined with our dedicated spectral fitting algorithm, we demonstrate highly selective multicompound analyses with less than 3.5% relative expanded uncertainty, even in the presence of a 40× excess of an interfering compound with complete spectral overlap.

Radiation-induced transformations of isolated phosphine molecules at cryogenic temperatures: Spectroscopic and chemical aspects

The radiation-induced transformations of isolated phosphine molecules in a series of solid noble gas matrices occurring under the action of X-rays at 4.5 K were studied by FTIR spectroscopy. It was shown that decomposition was quite efficient (the corresponding radiation-chemical yields of PH3 degradation were estimated as 5.8, 4.2, 3.5, and 2.0 molecules per 100 eV for neon, argon, krypton, and xenon, respectively). The radiolysis proceeds via two channels yielding PH2• and PH, respectively (the spectroscopic and kinetic data suggest that the latter species is partially trapped in the same cage with hydrogen molecules). Comparative studies using direct activation of isolated phosphine molecules in matrices at λ = 185 nm revealed similarity in the degradation pathways under radiolysis and VUV photolysis. Spectroscopic characteristics of the observed products and possible astrochemical implications of the results are discussed.

Collective stabilization through n→π* and P…π phosphorous bonding with cooperative halogen and hydrogen bonding in POCl3-Nitrile dimers: Matrix isolation infrared spectroscopic and ab initio computational studies

In the present study, the interaction between phosphoryl chloride (POCl3) with acetonitrile (CH3CN) and benzonitrile (C6H5CN) was explored using matrix isolation infrared spectroscopy and quantum chemical computations. The computations performed at MP2 and B3LYP-GD3 levels of theory with aug-cc-pVDZ basis set indicated the dominant mode of stabilization in POCl3-CH3CN (PACN) dimer is through n→π* (lp(O)…π*(CN)) interaction and for the POCl3-C6H5CN (PBCN) dimer it is predominantly by P…π phosphorous bonding interaction. Computations revealed that the nitrile moiety plays a significant role towards the stability in both the class of dimers. PACN heterodimer appears to be the first prototype, with the -CN moiety playing the acceptor through n→π* charge transfer interaction. The characteristic geometries of the heterodimers stabilized by n→π* and/or P…π interactions have been generated within inert gas matrixes at the cryogenic temperature of 12 K and identified using infrared spectroscopy. The interactions have been comprehensively characterized using quantum theory of atoms in molecules, natural bond orbital analysis, electrostatic potential mapping, energy decomposition and non-covalent interaction analyses.

Monitoring changes in the volatile fraction of roasted nuts and seeds by using comprehensive two-dimensional gas chromatography and matrix templates

Static headspace coupled with comprehensive two-dimensional gas chromatography and a flame ionization detector (HS-GC × GC-FID), has been applied to monitor changes in the volatile fraction of commercial edible nuts and seeds (peanuts, almonds, hazelnuts, and sunflower seeds). Effects of the roasting conditions (time, 5–40 min; temperature, 150–170 °C), which were employed under different combinations by using a ventilated oven, on target volatile fraction were examined to identify potential differences in relation to the roasting treatment of raw samples. In addition, reference templates were created, from the HS-GC × GC-FID method, for each of the four food matrices analyzed, and they were applied to characterize the samples according to the presence or absence of volatile compounds. Finally, these templates were successfully employed to make a quick distinction between different roasting conditions.•HS-GC × GC-FID was applied to study the volatile profile of edible nuts and seeds.•Reference templates (GC × GC-FID) were created for each of the four food matrices.•Rapid discrimination between raw and roasted samples was achieved.