Study of the thermal oxidation of polyolefines—VIII: Volatile products of polypropylene thermal oxidation

In the oxidation of isotactic polypropylene, qualitative and quantitative studies were made of organic volatile products by gas chromatographic methods. Experimental results and further data have been compared. Most of the products formed during degradation are acetone, and other ketones and aldehydes. Propylene, acetic acid and 2.4-dimethyl furane have also been identified.The products are formed in an accelerating kinetic process. There was linear relationship between the volatile products measured and the amount of oxygen consumption: approximately 2% of the oxygen absorbed is built into low molecular weight organic carbonyl compounds.     

Application of analytical pyrolysis for wood fire protection control

The effect of two flame-retardant compositions (A-76% potassium carbonate, B-67% sulphate ammonium) on the process of thermal degradation of wood and the composition of volatile products of pyrolysis has been investigated by the thermogravimetry and analytical pyrolysis methods. It has been shown that the effect of flame retardants manifests itself in the low-temperature region with the formation of more thermally stable intermediate carbonized products. Upon pyrolysis of wood under the action of the composition A, the mechanism of degradation of the lignin component changes, which manifests itself in a more than two-fold increase in the guaiacol and vinylguaiacol contents in the composition of volatile products and the inhibition of the formation of carbohydrates destruction products. It has been found that the composition B has a catalytic action mainly on the process of thermal depolymerization of cellulose, favouring the increase in the formation of levoglucosan and practically does not change the yield of lignin degradation products.     

Monitoring and Statistical Analysis of Formation of Organochlorine and Organobromine Compounds in Drinking Water of Different Water Intakes

The main drawback of drinking water chlorination involves the formation of quite hazardous disinfection by-products (DBPs), represented mainly by halogenated species. Based on the authors’ monitoring data since 2002, the prevalence of chlorine over bromine in the composition of volatile DBPs was shown for the drinking water in Ufa (Russia). However, the situation was completely reversed in the case of semi-volatile DBPs. The principal goal of the present study involved rationalization of the results of the long-term monitoring. Gas chromatography–mass spectrometry (GC-MS) was used for the qualitative and quantitative analysis of volatile DBPs. Identification of semi-volatile compounds was carried out with GC-MS, while gas chromatography with an atomic emission detector (GC-AED) was used for their quantification. A significant contribution of oxygen to the composition of semi-volatile compounds proves the decisive role of the dissolved organic matter oxidative destructive processes. Statistical analysis revealed notable linear correlations for trihalomethane and haloacetic acid formation vs. chlorine dose. On the contrary, halogenated semi-volatile products do not demonstrate any correlations with the water quality parameters or chlorine dose. Principal component analysis (PCA) placed them into separate groups. The results allow for proposing that formation of the organohalogenated species involved the fast penetration of bromine into the humic matter molecules and, further, their oxidative destruction by active chlorine.     

龙井茶特征香气成分分析及种类判别

采用顶空固相微萃取(HS-SPME)和气相色谱-质谱(GC-MS)联用技术分析了39份龙井茶叶中的挥发性成分,结合质谱数据库与保留指数,从24份西湖核心区龙井茶中获得了200余种挥发性化合物,这些挥发性成分中主要含有醇类、酯类、酮类、杂环类等化合物,经筛选得到26种共有组分.并采用主成分分析法(PCA)对24份西湖核心区龙井茶和15份疑似龙井茶进行了有效区分.该方法适用于茶叶的品质鉴定、真假识别、产地溯源等方面的研究,也为其他产品的挥发性成分分析提供参考.     

Using solid-phase microextraction combined with gas chromatography-mass spectrometry for the study of the volatile products of biosynthesis released by plants and microorganisms

Published data on the methods and results of study of profiles of volatile biologically active compounds are summarized and discussed. The leading role of gas chromatography-mass spectrometry combined with headspace solid-phase microextraction as an optimum analytical method for determining the qualitative and quantitative composition of volatile organic compounds in in vivo experiments is substantiated. The results of investigation of volatile organic compounds produced by micromycetes of the genus Fusarium are reviewed.     

Characteristic Volatile Fingerprints of Four Chrysanthemum Teas Determined by HS-GC-IMS

Volatile composition is an important feature that determines flavor, which actively affects the overall evaluation of chrysanthemum tea. In this study, HS-GC-IMS (headspace-gas chromatography-ion mobility spectrometry) was performed to characterize the volatile profiles of different chrysanthemum tea subtypes. Forty-seven volatiles of diverse chemical nature were identified and quantified. Partial least squares discriminant analysis (PLS-DA) revealed that four chrysanthemum teas were distinct from each other based on their volatile compounds. Furthermore, this work provides reference methods for detecting novel volatile organic compounds in chrysanthemum tea plants and products.     

Chromatographic quantitation at losses of analyte during sample preparation. Application of the modified method of double internal standard

Known methods of quantitative chromatographic analysis (calibration, external standard, internal standard and standard addition) require the application of sample preparation techniques without significant losses of analytes. If this condition cannot be satisfied, the compensation of these losses should be provided. The modification of known method of quantitative chromatographic analysis (double internal standard), implying the addition of two homologues (previous and following) of target analytes as internal standards into initial samples is considered. This approach permits us to compensate significant losses both analytes and standards at all stages of sample preparation. The advantages of this method are demonstrated on the examples of liquid-liquid extraction, head space analysis (HSA), distillation of volatile compounds with volatile solvents (concentration in condensates) and evaporation of volatile solvents (concentrating in the residues of solvents). In all cases the application of two homologues as internal standards provides accurate results (the typical relative errors are within 1-6%) at the values of a factor of composition distortion of initial samples (K', the definition is suggested) from 0.2 up to 4. These results are in accordance with general relationships between variations in any physicochemical properties of organic compounds within homologous series. The single found exception was the evaporation of volatile solvents (the open phase transition process) when to get the results with relative errors not more then +10% requires the minimal changes in the composition of initial samples (K' values should not be more then approximately 1.5).     

The thermal degradation of polysiloxanes: Part 6—Products of degradation of poly(tetramethyl-p-silphenylene siloxane) and copolymers with dimethylsiloxane

The volatile products of thermal degradation of poly(tetramethyl-p-silphenylene siloxane) and a series of copolymers with dimethylsiloxane have been separated and identified using principally gas chromatography-mass spectroscopy (GC-MS). The effect of temperature of degradation and copolymer composition on the pattern of products has been demonstrated. As the proportion of dimethylsiloxane structures in the copolymers is increased, the predominantly linear products give way to cyclics.     

Capillary gas chromatographic analysis of volatile and non-volatile organic acids from biological samples as the t-butyldimethylsilyl derivatives

A quantitative procedure for the analysis of volatile organic acids and lactic acid in silage is described. The samples were extracted with diethyl ether, derivatized by t-butyldimethylsilylation, and then separated by capillary gas chromatography. The same procedure was useful for the identification by gas chromatography/mass spectrometry of organic acids in samples such as the metabolic fermentation products of anaerobic bacteria.     

Volatile constituents of Festuca nigrescens, Phleum alpinum and Poa alpina from N. W. Italian Alpine pastures

The composition of the volatile fractions of three important grasses from sub-alpine N.W. Italian pastures, namely Festuca nigrescens Lam. non Gaudin (chewing fescue), Phleum alpinum L. (alpine timothy) and Poa alpina L. (alpine bluegrass) was investigated. The fresh aerial parts were collected at the flowering stage during the summer season. The volatile oils obtained from green tissues by steam distillation in a Clevenger-type apparatus, were analyzed by GC/FID and GC/MS. The oil yield was 0.04 +/- 0.01% weight/fresh weight bases for each of the investigated species. Several classes of compounds were found in the volatile fractions, including aldehydes, alcohols, acids, hydrocarbons, esters, ketones, terpenes, and phenolics. Qualitative and quantitative differences were observed.     

基于TG-FTIR的生物质催化热解试验研究

运用热重－傅里叶红外光谱联用技术(TG-FTIR)，以麦秸为研究对象，探讨催化与非催化条件下生物质的热解挥发分析出特性，分析研究热解温度、催化剂种类对生物质热解主要析出产物的影响。通过热重TG和DTG曲线，获得了相关热解特性参数及动力学参数。结果表明，添加NiO和CaO存在两个失重峰，并促进麦秸热解反应进行，降低表观活化能，其中NiO对提高热解析出产率作用更显著。通过红外光谱对热解产物实时测量的分析表明，CO与CO2的析出与失重峰基本一致，而CH4的析出滞后于前两者。添加NiO和CaO有利于减少热解产物中的CO2的浓度，促进挥发分产物CO、CH4的生成。其中CaO更有利于生物质在温度800℃以下的热解性能改善，而NiO在800℃以上具有更好的催化作用。     

New approach based on solid-phase extraction for the assessment of organic compound pollutions in so-called pharmaceutically pure water

The application of a new kind of technique involving solid-phase extraction coupled with thermal desorption (SPE-TD) to the qualitative analysis of water used in pharmaceutical products was evaluated. Comparative analyses performed by the purge and trap (PT) technique were also conducted. The application of this SPE-TD technique resulted in the isolation of a large number of compounds from the water sample. The SPE-TD technique is applied to less volatile compounds, whereas the PT technique is used for more volatile and nonpolar ones. These two techniques should be applied in order to achieve complete identification and quantitative determination. Additionally, an attempt to identify organic compounds in pharmaceutical products was also conducted. The compounds present in such products include aldehydes, ketones, hydrocarbons, alcohols, esters. The influence of storage on the quality of water was also investigated. For samples characterized by a longer storage time, qualitatively richer chromatograms were obtained, which confirmed that components were released from the packaging (especially polyethylene) which entered the stored product.     

Thermal degradation of polyethylene and polystyrene from the packaging industry over different catalysts into fuel-like feed stocks

Thermal degradation of waste polymers was carried out as a suitable technique for converting plastic polymers into liquid hydrocarbons, which could be used as feed stock materials. The catalytic degradation of waste plastics (polyethylene and polystyrene) was investigated in a batch reactor over different catalysts (FCC, ZSM-5 and clinoptillolite). The effects of catalysts and their average grain size on the properties of main degradation products (gases, gasoline, diesel oil) are discussed. The temperature range of 410-450 °C was used in the process. Both equilibrium FCC catalyst and natural clinoptilolite zeolite catalyst had good catalytic activity to produce light hydrocarbon liquids, and ZSM-5 catalyst produced the highest amount of gaseous products. Gases and liquids formed in cracking reactions were analyzed by gas chromatography. The liquid products consisted of a wide spectrum of hydrocarbons distributed within the C₅-C₂₈ carbon number range depending on the cracking parameters. The composition of hydrocarbons had linear non-branched structure in case of polyethylene, while from polystyrene more aromatics (ethyl-benzene, styrene, toluene, and benzene) were produced. The yields of volatile products increased with increasing degradation temperature. The olefin content of liquids was measured with an infrared technique and an olefin concentration of 50-60% was observed. The concentration of unsaturated compounds increased with decreasing temperature, and in the presence of catalysts. The activation energies were calculated on the basis of the composition of volatile products. The apparent activation energies were decreased by catalysts and catalyst caused both carbon-chain and double bond isomerisation.     

Sustainable routes for quantitative green selenocyanation of activated alkynes

By using cheap lactic acid as the recyclable catalyst and reaction media, a sustainable protocol for the synthesis of Z-3-selenocyanatoacrylates and analogues through green selenocyanation of activated alkynes has been achieved.     

Application of off-line pyrolysis with dynamic solid-phase microextraction to the GC–MS analysis of biomass pyrolysis products

Pyrolysis coupled with dynamic solid-phase micro extraction (Py-SPME) followed by GC–MS analysis was applied to the determination of volatile compounds evolved by a micro-scale off-line pyrolysis apparatus, in order to extend the information affordable with this type of analytical equipment. The Py-SPME method with a carboxen/PDMS fiber working in the retracted mode was tested on four biomass samples (switchgrass, sweet sorghum, corn stalk and poplar) for qualitative analysis of semi-volatile pyrolysis products and quantitative determination of main volatiles (C₁–C₄) pyrolysis products. The developed procedure allowed capturing and analysis of all GC analyzable compounds, without memory effects and with good peak resolution also for early GC-eluting compounds. Twelve main volatile pyrolysis products, including hydroxyacetaldehyde and acetic acid, were successfully quantified; in spite of the intrinsic variability introduced by dynamic SPME sampling, results were relatively accurate and consistent with literature data on bench pyrolysis reactors.     

Comparative analysis of the oil and supercritical CO(2) extract of Artemisia arborescens L. and Helichrysum splendidum (Thunb.) Less

Isolation of volatile concentrate from the dried leaves of Artemisia arborescens and of Helichrysum splendidum has been obtained by supercritical extraction with carbon dioxide. To obtain a pure volatile extract devoid of cuticular waxes, the extraction products were fractionated in two separators operating in series. A good extraction process was obtained operating at 90 bar and 50 degrees C in the extraction vessel, at 90 bar and at -5 degrees C in the first separator and at a pressure between 20 and 15 bar and temperatures in the range 10-20 degrees C in the second one. The composition of the volatile concentrate has been analyzed by GC/MS. The volatile concentrate of A. arborescens was found to contain: trans-thujone (13.96%), camphor (6.15%) and chamazulene (5.95%).The main constituents in the extract of H. splendidum were: germacrene D-4-ol (17.08%), germacrene D (9.04%), bicyclogermacrene (8.79%) and delta-cadinene (8.43%). A comparison with the oils obtained by hydrodistillation is also given.The differences observed between the composition of the SFE volatile concentrates and of the hydrodistilled (HD) oils were relevant. Indeed, the HD oils had a blue color whereas the volatile concentrates were pale yellow. The HD oil of H. splendidum had a blue color due to the presence of guaiazulene (0.42% vs 0%), whereas the coloration of HD oil of A. arborecens was due to the high concentration of chamazulene (26.64% vs 3.37%).     

Essential oil composition of Citrus medica L. Cv. Diamante (Diamante citron) determined after using different extraction methods

In this paper, we report the qualitative and quantitative composition of the volatile and the oxygenated heterocyclic fraction of citron (Citrus medica L. cv. Diamante (Diamante citron)). The fruits selected for the extraction were of three types: green citron of little size, green citron of big size, and yellow citron after 1 month from the harvest. The essential oils were extracted using three different methods. The nine samples of oil thus obtained were analyzed by high resolution GC (HRGC)‐flame ionization detection (FID), HRGC‐MS, and RP‐HPLC. They differ only in the quantitative composition, while the qualitative profile was the same. The volatile fraction of every sample of oil is characterized by a high content of limonene, γ‐terpinene, and monoterpene aldehydes and a lower content of α‐ and β‐pinene and myrcene, sesquiterpenes, and aliphatic aldehydes. Enantioselective (Es)‐GC analysis of the extracts allowed the determination of the enantiomeric distribution of five terpenoid compounds; a prevalence of four dextrorotatory isomers was observed. Oxypeucedanin was the main component of the oxygenated heterocyclic fraction in the extracts of green fruits, while citropten was the major oxygenated compound in the oil obtained from yellow citron.     

Statistical evalution of aroma and metal content in Tokay wines

Wine qualities are predominantly determined by the qualitative and quantitative composition of organic and inorganic components present, consequently elucidating them is one of the tasks of greatest significance facing wine analysis. It is, on the other hand, of unique importance from the economic viewpoint to make sure and keep a continuous check on whether wine qualities are satisfactory enough, taking the trend into consideration that nowadays among products for human consumption it is solely those that show a high likelihood to succeed on the market in the long run that manage to satisfy quality requirements of gradually increasing demands. Research into food analytic on the other hand, plays a considerably significant role in origin protection which is an issue of particular importance in the case of a wine-growing area of such long tradition. During the course of the investigation the answer was sought to the question of how qualitative and quantitative relations of volatile organic and metal components present in traditional wines produced in the wine-growing area depend on the vintage, the location on which it is grown, as well as the type of wine grape and to what extent these are characteristic of wines of given type and vintage.     

Applying the hydrodistillation process to Pentadiplandra brazzeana Baill. root: a chemical assessment

A chemical study of the volatile components obtained by applying the hydrodistillation and reflux processes to Pentadiplandra brazzeana roots was performed by GC-FID and GC-MS. The hydrodistillation process showed a total yield of 0.97% with 0.11% of essential oil and 0.86% of volatile compounds from the aqueous reaction medium; in the reflux process, the volatile extract yield was 1.03%. Benzylic-type isothiocyanates were the major degradation products of glucosinolates in the essential oil (95.0%); the CH₂Cl₂ extracts obtained from the aqueous solutions were characterised by alcohols and amines in both processes. This study has shown that during hydrodistillation, only 10% of the glucosinolate degradation products are recovered in the essential oil whereas 90% remain in the aqueous medium, being converted into alcohols and amines. The relative percentages of the different chemical classes recovered in our experimental conditions are discussed in relation with the glucosinolate composition in the raw material.     

The pyrolytic identification of organic molecules: I. The pyrolytic behavior of organic molecules

Results of a study on the pyrolysis of about 70 organic compounds of varied composition are presented and discussed. Identification of the volatile products formed was accomplished by mass spectrometry. It is shown how the pyrolytic patterns may be employed to distinguish one molecule from another. Some attention has been given to isomeric compounds and to aromatic structures containing one or more functional groups.