Oxidative degradation products of irradiated polyethylene

Oxidative thermal degradation products of polyethylenes at various temperatures crosslinked with electron beams have been analyzed with gas chromatography and mass spectrometry techniques. Carbon monoxide and carbon dioxide are determined at a temperature range of 200–340°C, and the activation energies of the unirradiated and the irradiated polyethylene (at 100 Mrad) are 13.5 and 11.4 Kcal/mole, respectively. C₁ to C₈ hydrocarbons produced in air and in nitrogen are determined at temperatures from 400 to 450°C for the polyethylenes. The irradiated polyethylene produces less hydrocarbons in air than the unirradiated polyethylene, contrary to the fact that the crosslinked polymer evolves more hydrocarbons than the unirradiated polymer in a nitrogen atmosphere. Aldehydes and ketones are observed in the volatile oxidative degradation products, and these carbonyl compounds increase quantitatively with increase of temperature up to about 460°C. It is concluded that irradiated polyethylene is thermally more unstable in the absence of oxygen and more easily oxidable at low degradation temperatures in air than unirradiated polyethylene. Irradiated polyethylene, however, is more heat-stable than unirradiated polyethylene from the standpoint of the ignition process.     

Identification of control parameters for the sulfur gas storability with bag sampling methods

Air samples containing sulfur compounds are often collected and stored in sample bags prior to analysis. The storage stability of six gaseous sulfur compounds (H₂S, CH₃SH, DMS, CS₂, DMDS and SO₂) was compared between two different bag materials (polyvinyl fluoride (PVF) and polyester aluminum (PEA)) at five initial concentrations (1, 10, 100, 1000, and 10,000 ppb). The response factors (RF) of these samples were determined after storage periods of 0, 1, and 3 days by gas chromatography–pulsed flame photometric detector (GC–PFPD) combined with an air server (AS)/thermal desorber (TD) system. Although concentration reduction occurred more rapidly from samples of the high concentration standards (1000 and 10,000 ppb), such trends were not evident in their low concentration counterparts (1, 10, and 100 ppb). As such, temporal changes in RF values and the associated loss rates of most sulfur gases were greatly affected by their initial concentration levels. Moreover, the storability of oxidized sulfur compound (SO₂) was greatly distinguished from that of reduced sulfur compounds (RSCs), as the former almost disappeared in the PVF bag even after one day. The results of our study confirm that storability of gaseous sulfur species is affected interactively by such variables as initial gas concentration level, bag material type, and oxidation status with the associated reactivity.     

Investigations into the characteristics of irradiated zircaloy cladding material in connection with reactor operation and spent fuel reprocessing

To monitor and improve the performance of nuclear fuel assemblies, the uptake of gases (oxygen, nitrogen and hydrogen) is determined in zircaloy cladding materials. Gas chromatography and/or mass spectrometry combined with hot vacuum fusion were applied. Deviations from the initial concentrations (ca. 5 μg g^?1 H₂, 30 μg g^?1 N₂ and 1200 μg g^?1 O₂) in the “as fabricated” condition, are important in estimating cladding corrosion. The material characteristics of zircaloy are altered substantially by the neutron irradiation and the chemical environment in the reactor coolant, thus the irradiated material must also be studied. For reprocessing safety consideration, the ignition and explosion parameters of unirradiated and irradiated zircaloy dusts were examined. Standard methods, tailored to hot-cell operation, were used to evaluate the minimum ignition temperature of a dust layer on a heated surface at constant temperature, the ignition temperature of a dust cloud, the auto-ignition temperature of a cylindrical dust formation as a function of sample volume, and the explosion pressure and pressure rise in a 20-l spherical chamber. Samples of fines (<100 μm diameter) were characterized by measuring their density and particle-size distribution, and by scanning electron microscopy. For samples of irradiated zircaloy, the ignition temperatures were lower and the explosion pressures and pressure rises higher than for unirradiated zircaloy. These findings can be explained by the different particle-size distribution of irradiated material samples. The increased brittleness of the irradiated material produces more small particles (<20 μm) which favour ignition and explosion.     

The Use of the Helium Ionization Detector for Gas Chromatographic Monitoring of Trace Atmospheric Components

Two different gas chromatographic detectors, the helium ionization detector (HID) and the more commonly used flame ionization detector (FID), were used in parallel to compare their responses to a number of organic compounds. Atmospherically important oxygenated species were analyzed, as well as hydrocarbons and chlorinated and sulfur containing organics. The HID exhibited the better response to all compounds investigated, most notably to formaldehyde and higher oxygenates. A gas chromatographic system was developed to trap and analyze atmospheric organic compounds with HID detection. This required careful choice of the adsorbent material and removal of inorganic components (namely nitrogen and oxygen) before analysis. Real air samples were then taken and analyzed qualitatively for a range of olefinic and aromatic compounds.     

Conductive properties of sintered zinc oxide surface. The influence of electron irradiation and oxygen adsorption

The influence of irradiation with 5 MeV electrons on charge transport phenomena in the surface region of sintered ZnO was studied in the temperature range 200–600 K. Mobility and concentration of electrons were measured in the presence and absence of oxygen as a function of temperature both for irradiated and unirradiated samples. The influence of electron beam processing was found most pronounced for ZnO samples with absorbed oxygen. Radiation induced desorption of O₂ was assumed to be responsible for enhanced effect of irradiation. Increased sensitivity of irradiated ZnO as an oxygen sensor has been observed and attributed to the formation of additional adsorption centres. A correlation between mobility of conduction electrons and their concentration in the surface region of irradiated ZnO with subsequently adsorbed oxygen was observed.     

热解析-气相色谱法测定印刷品中总挥发性有机化合物释放量

建立用气袋法收集整册印刷品释放的挥发性有机化合物,热解析-气相色谱法检测总挥发性有机化合物(TVOC)的方法。将印刷品样品置入充满高纯氮气的密封PVF采样袋中,在35℃下放置12 h后,用采样器串联Tenax-TA采样管和采样袋,让袋内气体通过采样管,样品释放出的有机化合物被吸附到采样管的吸附剂上。用热解析-气相色谱法测试采样管中挥发性有机化合物的含量,其中苯、甲苯、邻二甲苯、间二甲苯、对二甲苯、乙苯、乙酸丁酯、苯乙烯和正十一烷按外标法定量,其它物质按甲苯标准曲线定量。该方法的加标回收率为74.4%~91.1%,测定结果的相对标准偏差不大于10%(n=9)。该方法的样品采集更贴近印刷品的实际生活场景,可以为评价印刷品挥发性有机物释放对人体健康的影响提供数据基础,为相关评价提供新思路。     

Oxygen effect in the radiolysis of proteins:: V. Histones

Histones of calf thymus were irradiated with X-rays in different phosphate solutions under nitrogen and air. Degradation of the monomer core histones, formation of aggregates and of fragments were determined by electrophoresis and HPL-gelchromatography. Under nitrogen loss of monomer histones are caused by aggregation, under air by fragmentation. No influence of the different ionic conditions was observed. The G-value for degradation is smaller under air than under nitrogen. These results for histones are compared with the oxygen effect of other proteins.     

Identification of irradiation treatment of spices by thermoluminescence of contaminating minerals

Five spices, cumin, coriander, clove, cinnamon and black pepper were irradiated by gamma-ray doses of 1.0 and 5.0 kGy and thermoluminescence (TL) method was used for identification of the irradiation treatment. The TL response of the minerals isolated from irradiated samples was much higher as compared to the mineral particles from unirradiated control samples. For the normalisation of results the separated minerals were reirradiated to a normalisation dose of 1.0 kGy and the TL glow curve was recorded a second time. By comparing the glow curves of irradiated and unirradiated samples, finding the ratio of the areas of first and second glow curves (TL₁/TL₂) and comparing the shapes of the glow curves, all the irradiated and unirradiated samples were identified correctly.     

Trace analysis of small gas samples in sealed containers with mass spectrometry using static dilution

A sampling method for the analysis of small amounts of gases from sealed containers is described. Liquefied pressurised gas samples were expanded into a vacuum box and statically diluted with ultrapure nitrogen. The equations for the sample dilution were established, relating the measured impurity amount fractions in the sample mixture to their partial pressures in the sealed container and, in the case of oxygen, to the air pressure. Ion?Cmolecule reaction mass spectrometry allowed identification and measurement of trace impurities corresponding to partial pressures in the range of 1?hPa in the container. The method was applied for determining the identity and amount of gaseous impurities in n-butane used in implantable gas pressure?Coperated drug infusion pumps. Impurities from the n-butane supply cylinder or from decomposition products, for example due to the laser welding of the Ti plugs of the containers, could be excluded by the results of saturation vapour pressure measurements, FID gas chromatograms and IMR mass spectra. The variability in pressure versus volume among tested infusion pump samples was associated with excess oxygen, attributable to an excessive residual air pressure in the gas containers before they were filled with n-butane. The sample preparation method is principally applicable to measure the composition of small amounts of gas mixtures and gaseous impurities with identified IMR mass spectra down to trace levels??even for ubiquitous substances like oxygen. The volume of the produced gas mixtures allows characterisation of the gas by standard gas analytical methods and for impurities by trace gas analytical methods.     

Remotion of organic compounds of actual industrial effluents by electron beam irradiation

Organic compounds has been a great problem of environmental pollution, the traditional methods are not effecient on removing these compounds and most of them are deposited to ambient and stay there for long time causing problems to the environment. Ionizing radiation has been used with success to destroy organic molecules. Actual industrial effluents were irradiated using IPEN's electron beam wastewater pilot plant to study organic compounds degradation. The samples were irradiated with and without air mixture by different doses. Irradiation treatment efficiency was evaluated by the Cromatography Gas Analyses of the samples before and after irradiation. The studied organic compounds were: phenol, chloroform, tetrachloroethylene (PCE), carbon tetrachloride, trichloroethylene (TCE), 1,1-dichloroethane, dichloromethane, benzene, toluene and xilene. A degradation superior to 80% was achieved for the majority of the compounds with air addition and 2kGy delivered dose condition. For the samples that were irradiated without air addition the degradation was higher.     

DBD Plasma Treatment of Titanium in O2, N2 and Air

Dielectric Barrier Discharge plasma treatment of a titanium metal foil in oxygen, nitrogen and air under atmospheric conditions is investigated employing X-Ray Photoelectron Spectroscopy (XPS). We investigated three different reference samples and compare the results with a large number of studies on the XPS analysis of titanium compounds containing oxygen and nitrogen. The plasma treatment in all three different process gases leads to the formation of titanium dioxide films, while rather small nitrogen fractions are found after nitrogen and air plasma treatments. This finding is explained basing on plasma chemistry insight from the literature.     

Comparison of storage stability of odorous VOCs in polyester aluminum and polyvinyl fluoride Tedlar bags

Whole air sampling using containers such as flexible bags or rigid canisters is commonly used to collect samples of volatile organic compounds (VOC) in air. The objective of this study was to compare the stability of polyester aluminum (PEA) and polyvinyl fluoride (PVF, brand name Tedlar^®) bags for gaseous VOC sampling. Eight VOC standards (benzene, toluene, p-xylene, styrene, methyl ethyl ketone, methyl isobutyl ketone, butyl acetate, and isobutyl alcohol) were placed into each bag at storage times of 0, 2, and 3 days prior to analyses by gas chromatography/mass spectrometry (GC/MS). From each bag representing each storage day, samples of 3 different mass loadings were withdrawn and analyzed to derive response factors (RF) of each chemical between the slope of the GC response (y-axis) vs. loaded mass (x-axis). The relative recoveries (RR) of VOC, if derived by dividing RF value of a given storage day by that of 0 day, varied by time, bag type, and VOC type. If the RR values after three days are compared, those of methyl isobutyl ketone were the highest with 96 (PVF) and 99% (PEA); however, the results of isobutyl alcohol were highly contrasting between the two bags with 31 and 94%, respectively. Differences in RR values between the two bag types increased with storage time, such that RR of PEA bags (88 ± 10%) were superior to those of PVF bags (73 ± 22%) after three days, demonstrating that VOC in PEA bags were more stable than in PVF bags.     

Identification of irradiated pulses by thermoluminescence of the contaminating minerals

Thermoluminescence (TL) response of contaminating minerals from six samples of pulses commonly consumed in Pakistan has been studied for identification of irradiation treatment. The samples were irradiated by Co-60 gamma rays at 0.3, 0.5 and 1.0 kGy, or by 10 MeV electrons using an accelerator at 0.75 and 2.2. kGy. Generally, the TL intensity for minerals separated from irradiated samples was higher than for unirradiated samples. To normalize the results, separated minerals deposited on stainless steel discs were re-irradiated by a normalizing dose and TL response was redetermined. The ratio of the area of the first glow curve to the second glow curve was more than 0.8 for all irradiated samples and less than 0.33 for most of the unirradiated samples. For those unirradiated samples where the ratio of the glow curves was more then 0.03, the shapes of the glow curves were compared. Taking this criterion into consideration, all 21 unirradiated and irradiated samples of pulses were identified correctly. Therefore, a normalization procedure by re-irradiation of minerals and analysis of TL glow curve shapes lead to unequivocal identification of radiation treatment of pulses.     

Simultaneous TG/DTG–DSC–FTIR characterization of collagen in inert and oxidative atmospheres

In this paper, a TG/DTG–DSC–FTIR study of type I collagen extracted from bovine Achilles tendon both in inert (nitrogen) and oxidative atmosphere (synthetic air and oxygen) from room temperature to 700 °C was performed. The thermal analysis results have shown that after initial dehydration, collagen exhibits a single decomposition step in nitrogen (due to pyrolysis), while in air and oxygen two steps are observed due to thermo-oxidative decomposition, the latter being highly exothermic. The CO₂ bands dominate the FTIR spectra of evolved gases in all atmospheres (especially in air and oxygen), along with the characteristic bands of ammonia, water, HNCO, methane. In nitrogen, the bands of pyrrole, HCN, and ethane were also identified, while in oxidative atmospheres, nitrogen oxides and CO are released. A study was also performed by comparing the DTG and gas evolution curves observed for the three atmospheres.     

Complexity of ammonia interactions on activated carbons modified with V2O5

A micro/mesoporous wood-based activated carbon was modified with different loadings of vanadium pentoxide via incipient impregnation with ammonium vanadate solution followed by heating in nitrogen at 500 degrees C. The materials were used as adsorbents for ammonia. Both adsorption and desorption curves were recorded. The initial and exhausted samples were characterized by Fourier transform infrared spectroscopy (FTIR), potentiometric titration, thermal analysis and adsorption of nitrogen. An improvement in ammonia uptake compared to the virgin carbon was observed, and the adsorption capacity was found linearly dependent on the metal content. Water increases ammonia adsorption capacity via dissolution of the gas, but it also competes with ammonia because both of them are preferentially adsorbed on the same vanadium oxide sites (vanadyl oxygens). Even though an increase in the interactions strength between ammonia and the adsorbents' surface has been reached compared to previous studies, some weakly adsorbed ammonia was still released from the surface during air purging.     

Molecular-topological and thermal properties of gamma-irradiated alternating carbon monoxide-ethylene copolymer

Gamma-irradiation to a dose of up to 2000 kGy does not lead to substantial changes in the topological structure of a carbon monoxide copolymer with ethylene, thereby suggesting it high radiation resistance. The topological structure of unirradiated and irradiated copolymer samples is polyblock in nature having four crystalline phases as the branching “junctions” in the pseudo-network structure of its amorphous block. Copolymer molecular flow begins after completion of melting of its high-melting fraction and at an onset flow temperature of 484 ± 4 K regardless of the absorbed radiation dose. The irradiated and unirradiated copolymer releases the same gaseous products upon heating, and the irradiation itself does not affect the onset temperature of effective gas evolution.     

Emission pattern of semi-volatile organic compounds from recycled styrenic polymers using headspace solid-phase microextraction gas chromatography–mass spectrometry

The emission of low molecular weight compounds from recycled high-impact polystyrene (HIPS) has been investigated using headspace solid-phase microextraction (HS-SPME) and gas chromatography–mass spectrometry (GC–MS). Four released target analytes (styrene, benzaldehyde, acetophenone, and 2-phenylpropanal) were selected for the optimisation of the HS-SPME sampling procedure, by analysing operating parameters such as type of SPME fibre (polarity and operating mechanism), particle size, extraction temperature and time. 26 different compounds were identified to be released at different temperatures from recycled HIPS, including residues of polymerisation, oxidated derivates of styrene, and additives. The type of SPME fibre employed in the sampling procedure affected the detection of emitted components. An adsorptive fibre such as carbowax/polydimethylsiloxane (CAR/PDMS fibre) offered good selectivity for both non-polar and polar volatile compounds at lower temperatures; higher temperatures result in interferences from less-volatile released compounds. An absorptive fibre as polydimethylsiloxane (PDMS) fibre is suitable for the detection of less-volatile non-polar molecules at higher temperatures. The nature and relative amount of the emitted compounds increased with higher exposure temperature and smaller polymeric particle size. HS-SPME proves to be a suitable technique for screening the emission of semi-volatile organic compounds (SVOCs) from polymeric materials; reliable quantification of the content of target analytes in recycled HIPS is however difficult due to the complex mass-transfer processes involved, matrix effects, and the difficulties in equilibrating the analytical system.     

The Analysis of Sulfur Compounds by Solid Adsorbent Tenax GR Preconcentration and Gas Chromatography with Flameless Sulfur Chemiluminescence Detection

Gas chromatography using flameless sulfur chemiluminescence detection was applied to the analysis of sulfur compounds in air. A trap employing the solid adsorbent Tenax GR was used to enrich ambient levels of volatile sulfur compounds. The sulfur gases were then thermally released according to programmed temperature from the adsorbent trap and re-collected in a column cooled with liquid nitrogen. The sulfur compounds were revolatilized and directly transferred to the system of PLOT-column gas chromatograph/flameless sulfur chemiluminescence detector for analysis. The PTV injector has been used as a thermal resorption chamber for analysis of sulfur compounds. The sulfur gaseous compounds known to cause nuisance odors in the air from sewerage treatment works were determined.     

The influence of γ-rays irradiation on the structure and crystallinity of heteropoly acid doped PVA

This contribution represents the manufacturing of a hybrid organic–inorganic proton conducting compound, which involves the introduction of heteropoly acid (HPA) of different concentrations into poly-vinyl alcohol (PVA). These compounds were irradiated by γ-rays at different doses of 10, 20, 30, and 40 kGy. The unirradiated and irradiated compounds were characterized by XRD and DSC. The XRD results showed that the crystallinity and d-spacing were strongly influenced by the amount of HPA and irradiation doses. The DSC results showed that the melting point was decreased as a result of HPA concentration and irradiation doses. The degree of crystallinity calculated from XRD is in good agreement with that calculated from DSC. The activation energy of the Unirradiated and irradiated compounds was calculated using the Flynn–Wall–Ozawa model.     

Organic metabolites in exhaled human breath—A multivariate approach for identification of biomarkers in lung disorders

The gas chromatographic profiles of exhaled air from lung cancer patients have been investigated. The breath from healthy volunteers, smokers and non-smokers, and lung cancer patients without treatment and under radio and/or chemotherapy, was collected using Tedlar bags. Different profiles for healthy people and cancer patients could be recognized by multivariate analysis and significant diagnostic compounds could be established. Target compounds showed to be linear and branched hydrocarbons between C₁₄ and C₂₄. Solid phase microextraction (SPME) coupled to gas chromatography mass spectrometry GC–(TOF)-MS was used. The method showed good precision (RSD below 26%) and limit of detection ranged from 0.04 to 8.0 ppb. These findings show a high potential for establishment of laboratorial screening methods. Validation studies in a larger number of patients are being done.