1,721,014 research outputs found
Pyrolysate composition and silylation efficiency in analytical pyrolysis of glucans as a function of pyrolysis time
No full textThe pyrolytic behaviour of two oligosaccharides – cellobiose and cellohexose – was studied using reactive pyrolysis-GC/MS with in situ hexamethyldisilazane derivatisation. Pyrolysis was conducted in a sealed vessel at various times ranging from 0.2 to 60 min. Semi-quantitative calculations were carried out on integrated peak areas to obtain information on derivatisation efficiency and composition of the pyrolysate as a function of pyrolysis time. The results were compared with a previous work by us in which glucose and cellulose were studied with the same procedure. The relative areas of anhydrosugars were found to decrease with the increase of the degree of polymerisation of the substrate, while the derivatisation efficiency showed an opposite trend. The results were explained by considering the role of both the sealed environment and water molecules freed during the pyrolysis process. We hypothesised that higher amounts of water were released from glucans with low degrees of polymerization, hindering both secondary pyrolysis reactions and derivatisation efficiency. Glucans with high degrees of polymerization, on the contrary, showed high signals of secondary pyrolysis products, consistent with a lower amount of water and the formation of a liquid phase
Characterization of volatile and non-volatile fractions of spices using evolved gas analysis and multi-shot analytical pyrolysis
Full text linkIn the present work, evolved gas analysis-mass spectrometry (EGA-MS) and analytical pyrolysis coupled with gas chromatography/mass spectrometry (Py-GC/MS) were used to characterize both the volatile and non-volatile fractions of six commercially available spices. Analysis of spices is usually performed through the study of their headspace composition by solid phase microextraction (SPME). In this new approach, EGA-MS was used to establish thermal degradation regions, and Py-GC/MS was used to obtain compositional information on each region separately using double-shot pyrolysis. This study demonstrates that EGA-MS and Py-GC/MS provide the same advantages of solid-phase micro extraction and increase the range of detectable products by performing high-temperature desorption and degradation of the non-volatile fraction of spices. Our approach provided both qualitative and semi-quantitative data that could be used in the future to improve authentication studies by considering the results not only of headspace composition, but also on the pyrolytic behavior of the lignocellulosic matrix
Evolved gas analysis-mass spectrometry and isoconversional methods for the estimation of component-specific kinetic data in wood pyrolysis
Full text linkThe pyrolysis reactions of hardwood and softwood were investigated using evolved gas analysis and mass spectrometry (EGA-MS) and by treating the experimental data with isoconversional methods to obtain kinetic information. Mass spectrometric detection allowed the identification of the pyrolysis products to be performed and component-specific thermograms were obtained by the extraction of appropriate m/z values without the need of peak-fitting. Finally, isoconversional methods, both an integral and a differential method, were used on compound-specific thermograms to calculate apparent activation energies of the carbohydrate and lignin fractions separately. The results showed that the two isoconversional methods provide comparable results, and that there are significant differences between the activation energies of the holocellulose and lignin fractions. This work shows that EGA-MS can provide reliable kinetic data for multi-component samples without the need of chemical pre-treatments or signal deconvolution
Analytical pyrolysis and thermal analysis to chemically characterise bitumen from Italian geological deposits and Neolithic stone tools
Full text linkThe chemical study of bitumen from stone tools from Italian Neolithic sites was carried out using analytical pyrolysis-based techniques, EGA-MS (evolved gas analysis mass spectrometry) and DSPy-GC/MS (double shot pyrolysis-gas chromatography/mass spectrometry). The study was mainly aimed at demonstrating the suitability of analytical pyrolysis for studying archaeological bitumen and for obtaining information regarding its origin. EGA-MS was employed to obtain information on the thermal complexity, that is the set of thermal properties and behaviours, of the samples and on their thermal degradation areas and DSPy-GC/MS along with Principal Component Analysis (PCA) were tested for biomarker analysis to assess bitumen source in archaeological objects. Geological bituminous rocks from Central-Southern Italy were selected and used as reference materials to both optimize experimental parameters and to support data interpretation for archaeological samples. Geological samples were also preliminary characterised by thermogravimetric analysis coupled with FTIR spectroscopy (TG-FTIR) under nitrogen and by TG analysis under oxygen to quantify their relative content of organic and inorganic species. The combination of thermal analysis and analytical pyrolysis-based techniques allowed us to quantify the organic content of the bitumen samples and to obtain information on both soluble and insoluble organic fractions. In addition, the proposed approach highlighted the main degradative patterns and the main differences among samples coming from different geographical areas as well as differences between geological and archaeological bitumen. Finally, DSPy-GC/MS associated with PCA proved to be successful in assessing the bitumen source in archaeological objects by the detection of terpanes, distinctive biomarkers
Composite gems in medieval era: the art of counterfeiting before the sixteenth century
No full textThis study explores the evolution of gemstone treatments, with a particular focus on composite gems, which consist of two or three layers of natural gems or artificial materials glued together with adhesives and pigments to imitate genuine natural gems (e.g. doublets and triplets). While traditional treatments such as foiling and coating are well documented, composite gems are largely absent from ancient literature. Pliny is the earliest source to mention the practice of gem imitation, even though with some condemnation. After a considerable gap, the first description of doublets and triplets appear in Leonardi (1502) and Cellini (1568), with the first literature reference to composite gems on goldwork dated to the fourth decade of the fifteenth century. The analysis of a collection of goldsmithing artifacts, dating from the late thirtheenth to the fifteenth centuries and preserved in Tuscany museums, revealed—for the first time—the unexpected presence of composite gems alongside a variety of gemstones and treatment methods. Gemological analysis, including Raman spectroscopy, and the study of adhesives using pyrolysis gas chromatography coupled with mass spectrometry, have shed light on their manufacturing processes. The results suggest that composite gemstones, particularly doublets and triplets, have been systematically produced in specialized workshops since the thirteenth century. This production is likely to have coincided with advances in the technology of cutting precious stones and artificial glass. This research not only sheds light on historical gemstone craftsmanship but also opens new perspectives for studying the evolution of gemology, challenging previous assumptions about the timeline and context of composite gemstone production
Low- and high-molecular weight fractions of geological ambers detected by evolved gas analysis-mass spectrometry
Full text linkWe used evolved gas analysis-mass spectrometry (EGA-MS) to characterize a pool of ambers belonging to different geological varieties, with the aim of obtaining information on both their non-polymeric and polymeric components. Small molecular components can be trapped in amber during the fossilization process. Their characterization can provide insights into the maturation process of amber and help in determining its age and botanical origin. Most of the analyzed ambers showed two gas evolution regions, corresponding to the desorption of low-molecular weight compounds at low temperature, and to the pyrolysis of the macromolecular matrix at high temperature. We established characteristic m/z signals of the non-polymeric and polymeric fractions, and we were able to classify most of the samples in agreement with the available literature. We also performed principal component analysis of diterpenoid ambers using their average mass spectra. This allowed us to differentiate between succinite and rumanite ambers, which showed very similar spectra. The results demon-strate that EGA-MS constitutes a reliable technique to obtain information on the molecular composition of ambers, and on their relative content of low-and high-molecular weight fractions
Effects of Milling and UV Pretreatment on the Pyrolytic Behavior and Thermal Stability of Softwood and Hardwood
No full textUV/visible light is a promising radiation source for biomass pretreatment, but very little knowledge is available on the effect of UV on the thermal behavior of lignocellulose in comparison with more classical, physical pretreatment methods. In this paper, we investigate the effects of ball-milling and UV irradiation on two species of softwood and two species of hardwood, using X-ray diffractometry (XRD), evolved gas analysis-mass spectrometry (EGA-MS), and pyrolysis-gas chromatography coupled to mass spectrometry (Py-GC/MS). The XRD data showed that the crystalline fraction of cellulose was destroyed by milling, but not by irradiation. The EGA-MS data and isoconversional kinetic analysis showed that both milling and irradiation can reduce the thermal stability of wood up to a limit value. The Py-GC/MS data showed that irradiation caused the most significant changes in the pyrolytic behavior of the wood species, increasing the ratio of holocellulose to lignin pyrolysis products and the reactivity of cellulose toward the derivatizing agent. Softwoods were more affected by irradiation than hardwoods. This paper shows that UV irradiation can decrease the recalcitrance of biomass toward pyrolysis, but its efficiency is highly dependent on the type of lignocellulosic substrate
Co-pyrolysis of wood and plastic: Evaluation of synergistic effects and kinetic data by evolved gas analysis-mass spectrometry (EGA-MS)
Full text linkCo-pyrolysis of biomass and plastics gives rise to synergistic effects that can improve the properties of the resulting bio-oil. In this paper, the co-pyrolysis of lignocellulose (softwoods and hardwoods) and plastic (polyethylene and polystyrene) mixtures at different ratios was investigated by evolved gas analysis-mass spectrometry (EGA-MS). Through the extraction of specific sets of m/z values, we were able to build component-specific thermograms representative of each component of the mixtures. Such thermograms were used to evaluate the presence of synergistic effects by the comparison with the theoretical thermograms. The shift of the peak temperatures and the differences between the integrated area of the two thermograms showed that both biomass and plastic influence the pyrolytic behaviour of the other component. Finally, the KAS model-free isoconversional method was used on component-specific thermograms to determine apparent activation energies of the biomass and plastic fractions
Degradation of wood by UV light: A study by EGA-MS and Py-GC/MS with on line irradiation system
Full text linkUV degradation of wood is an important phenomenon that entails loss of aesthetic and mechanic properties. The changes are usually studied with artificial ageing followed by spectroscopy, and focus on colour changes. Analytical pyrolysis coupled with gas chromatography-mass spectrometry (Py-GC/MS) and evolved gas analysis-mass spectrometry (EGA-MS) are powerful tools for wood characterisation, but the change in pyrolytic behaviour of wood after UV irradiation is not well documented. In this work, a new instrumental setup was used to perform UV irradiation on line with EGA-MS and Py-GC/MS with in situ derivatisation of fir and chestnut wood. The effect of UV exposure was evaluated in terms of thermal stability and composition of the pyrolysate. TThe results showed that UV degradation of the samples was mainly related to the lignin fraction, and significant differences were observed between the two species. Fir wood, showed extensive degradation after 4 hours of irradiation, while chestnut wood, showed very small changes. Qualitative comparison of the EGA-MS profiles and semi-quantitative analyses of the composition of the pyrolysates revealed that these techniques could be used as a fast monitoring tool to assess the UV degradation of wood
Study of thermal behavior and molecular composition of mixtures of resinous materials and beeswax found as adhesives in archaeological finds
Full text linkBeeswax and resinous materials have been used and combined since ancient times to obtain adhesives. In this work, we studied mixtures of these two materials under heating to investigate the effect of their interactions on the properties of the resulting adhesive. The results were then compared with those of archaeological samples, to obtain new insights into ancient technological knowledge. This study was performed by combining two different chemical-analytical techniques: evolved gas analysis coupled with mass spectrometry and flow injection analysis -high resolution mass spectrometry. Evolved gas analysis was used to investigate the thermal behavior of the mixtures and obtain information on production techniques and ageing processes. The data were processed by isoconversional method to estimate the activation energies associated with the thermal degradation of the ad-hesives. The results suggested that archaeological mixtures were subjected to a thermal pre-treatment before their use as adhesives and that heating led to a material with new chemical features, due to the formation of hybrid species between resin diterpenes and the beeswax compounds. The formation of these species was confirmed by high resolution mass spectrometry
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