High-energy collision-induced dissociation of small polycyclic aromatic hydrocarbons

High-energy collision-induced dissociation (CID) experiments on polycyclic aromatic hydrocarbons (PAHs) having 2-6 rings, naphthalene, anthracene, phenanthrene, fluoranthene, pyrene and coronene, were performed, and the relative abundances of their fragment ions were investigated as a function of collision energy. The results revealed that the PAHs except naphthalene showed a bimodal-type distribution of positive fragmentation ions, which is closely similar to the fragment-ion distribution reported for the CID of three-dimensional fullerene, C(60)(+) and C(70)(+). The three-ring isomers of anthracene and phenanthrene and the four-ring isomers of fluoranthene and pyrene can be distinguishable in their spectra under an electron ionization energy of 70 eV, but the high-energy CID spectra of the three- and four-ring isomers were almost identical. The fragmentation corresponding to fragment ions in the low-mass region of the bimodal CID spectra could be interpreted by the simple statistical model that fragment ions are formed by random evaporation from the molecular ions after a considerable structural rearrangement, 'phase transition', occurring at some high-energy state.     

Electroinitiated polymerization of trioxane in chlorinated hydrocarbons

The electroinitiated polymerization of trioxane in chlorinated hydrocarbons, with tetrabutyl-ammonium perchlorate as background electrolyte, has been investigated. The initiation always involves perchlorate oxidation but the polymerization exhibits different features in the various solvents. It has been found that in 1–2 dichloroethane the polymerization, once started by a short pulse of current, proceeds without any induction period to moderate conversion of monomer to polymer. The initial rate of polymerization depends linearly on the monomer cone, and on the initiating charge, so allowing determination of some kinetic parameters. On the other hand, the electroinitiated polymerization of trioxane in dichloromethane requires continuous current to give reasonable conversions; it exhibits induction periods and acceleration which cannot be simply related to the current.     

Electroinitiated polymerization of 1,3-dioxolane in chlorinated hydrocarbons

The electrochemically initiated polymerization of 1,3-dioxolane has been investigated in 1,2-dichloroethane with tetrabutylammonium perchlorate as background electrolyte.The anode process is due to the monomer, and its intermediate oxidation products are probably the initiating species; once initiated, the polymerization reaches an equilibrium which is largely independent of the amount of the initially furnished charge.The conversion at equilibrium on the contrary depends on temperature and initial monomer concentration. The kinetic curves at 50° do not exhibit induction and acceleration periods but autocatalysis becomes important at lower temperature.The polymerization seems slower in dichloromethane, but the process trends to the same equilibrium conversion.The molecular weight of the polymers depends on temperature, monomer concentration and amount of initiating charge: apart from some chain transfer acting in the first stage of polymerization, the process exhibits “living” features in the increase of molecular weight with conversion.     

Trends of volatile chlorinated hydrocarbons and trihalomethanes in Antarctica

In order to understand behaviour and environmental fate of manmade chemicals in remote and cold areas, during the XXVII Italian Expedition carried out in Antarctica throughout the austral summer 2011/2012, superficial snow and lake water were sampled along the Ross Sea's South coast and their content of some low-molecular weight volatile halogenated hydrocarbons was evaluated. In consideration of their important role in stratospheric ozone chemistry, some volatile chlorinated hydrocarbons (VCHCs) and trihalomethanes (THMs) were investigated. The analyses were realised with a dedicated system composed by a purge-and-trap injector coupled to a gas chromatograph with a mass spectrometer (PTI-GC-MS) operating in SIM mode. The investigated VCHCs (chloroform; 1,1,1-trichloroethane; tetrachloromethane; trichloroethylene and tetrachloroethylene) were present in all analysed samples, and concentration levels ranged from units to hundreds of ng L^?1 according to considered matrix. For the first time, THMs (bromoform; dibromochloromethane; bromodichloromethane), were measured in Antarctic lake waters and freshly deposited snow; their concentration levels ranged from units to tens of ng L^?1. In order to assess eventual temporal variations, VCHC content in aqueous Antarctic matrices was compared with levels occurring in the past Italian Antarctic expeditions: for some banned substances, a decrease in concentration was observed, probably due to worldwide use restrictions. Finally, current Antarctic and Italian VCHC and THM levels in snow and lake water samples were compared and were found to be quite similar, differing at most by one order of magnitude, corroborating the hypothesis of an accumulation of halogenated compounds in Antarctic aqueous matrices.     

Extraction of chlorinated hydrocarbons from fish with sulphuric acid

A method is described for extraction of chlorinated hydrocarbons (DDTs and PCBs) from fish samples with sulphuric acid of various concentrations. The results are better than those obtained by an official method using Soxhiet extraction with n-hexane, especially with 9.5-13M sulphuric acid. The relative standard deviation is about 12% for analysis of portions of a homogenized single sample taken from the dorsal flesh of the same fish. Drawbacks and advantages in comparison with other methods are discussed.     

Capture of volatile chlorinated hydrocarbons by aqueous solutions of branched cyclodextrins

The use of aqueous solutions of branched cyclodextrins was examined in order to develop an effective method of capturing toxic volatile chlorinated hydrocarbons such as trichloroethylene and monochlorobenzene. From the experiments in which trichloroethylene diluted with nitrogen gas came into contact with aqueous solutions of branched cyclodextrin mixtures, it was found that absorption could be performed without the formation of inclusion complex solids, which should simplify the whole process of absorption and recovery.     

氮气中六种氯代烷烃混合标准气体的研制

介绍了氮气中6种氯代烷烃混合标准气体的制备和定值方法。标准气体的组分是二氯甲烷、三氯甲烷、1,1-二氯乙烷、1,2-二氯乙烷、1,1,1-三氯乙烷和1,1,2-三氯乙烷,标准值为5 μmol/mol。考察了标准气体的制备重现性、均匀性和稳定性。结果表明,标准气体在气瓶内均匀性良好,扩展相对不确定度为5%,使用有效期为一年。经与国外的同类标准气体比对,量值有较好的一致性。氮气中6种氯代烷烃混合标准气体的研制为挥发性氯代烷烃的检测提供了计量标准。     

预测氯代芳烃对戈卑鱼毒性的理论研究

为建立氯代芳烃对戈卑鱼毒性相关的QSAR模型,分析了22种氯代芳烃的结构特征,计算了各个分子的分子连接性指数.通过多元线性逐步回归分析研究,筛选了其中4种分子连接性指数~0X,~2X,~3X和~4X_(PC),建立了这4种指数与氯代芳烃对戈卑鱼毒性的定量结构-活性相关的QSAR模型,方程的相关系数R=0.979,判定系数R_(adj)~2=0.959,标准误差S=0.134,经检验该模型具有良好的稳定性和预测能力.     

Determination of chlorinated hydrocarbons in single and multi component test gases

Summary For comparing the efficiency of active and diffusive sampling methods two diffusive samplers with different properties were used to determine chlorinated hydrocarbons (CH₂Cl₂, CHCl₃, CCl₄) in single and multi component test gas mixtures. One of the chosen diffusive samplers can also be used for active sampling.In general, good correlations of all tested methods could be observed in the direct comparison of active and diffusive sampling and in the determination of the efficiencies.During the application of active and diffusive sampling methods in multi component test gases of the analytes possible interferences could not be ascertained.     

Noble metal loaded zeolites for the catalytic oxidation of chlorinated hydrocarbons

Summary A series of metal loaded zeolite catalysts (Pd/H-ZSM-5, Pd/H-BETA, Pt/H-ZSM-5, and Pt/H-BETA) were investigated for their activity and selectivity during oxidation of different chlorinated hydrocarbons, namely dichloromethane and trichloroethylene, at constant gas space velocity (15,000 h^-1) and constant chlorohydrocarbon concentration (1,000 ppm in dry air). It was observed that the two noble metals played a major role in influencing the catalytic performance for complete oxidation of both chlorinated compounds. The acidic properties of the zeolite support in combination with increased oxygen activation owing to the noble metal were responsible for the high chlorocarbon destruction activity exhibited by this type of catalysts.     

Methods for the analysis of persistent chlorinated hydrocarbons in tissues.

Chlorinated hydrocarbons bioaccumulate in tissues and may have severe health consequences. These compounds occur individually, in small groups or as complex mixtures; examples of each category include aldrin, hexachlorocyclohexane and the polychlorinated biphenyls. Tissue extraction and purification schemes have been established, although new approaches such as supercritical fluid extraction are promising. Analyses often require the resolving power of capillary gas chromatography, in combination with the sensitivity and selectivity of electron-capture detection, electrolytic conductivity detection and mass spectrometry. Difficulties arise in quantitating chlorinated hydrocarbons in tissues, due to the number of components present and the fact that individual constituents may be reduced or enhanced in concentration in tissues, compared with the original formulation. Congener specific analysis and computer-assisted identification techniques have been applied to the problem.     

Surface grafting of polyethylene by mutual irradiation in methyl acrylate vapor. II. High-energy electrons irradiation

Vapor-phase mutual grafting of methyl acrylate (MA) onto polyethylene (PE) at high dose rates from an electron accelerator yields the same surface graft structure as does the grafting at low dose rates from ⁶⁰Co sources; i.e., a homopolymer layer (consisting of only MA component) is easily formed on the inner graft copolymer layer (consisting of both MA and PE components) as a result of the continuously increasing surface graft composition. To produce the surface layer, 4-MeV electron irradiation with a linear electron accelerator requires only less than 3 min of irradiation time at dose rates of more than 2 Mrad/min, whereas γ irradiation with a ⁶⁰Co source requires at least 1 hr at dose rates of less than 2 × 10³ rad/min. The rate of monomer consumption (or polymerization) in the surface homopolymer layer shows no dependence of irradiation time and a positive dependence of dose rate. It has been suggested that this kinetic feature at the high dose rates shows some contribution of vapor-phase homopolymerization and subsequent deposition (onto the grafting surface) followed by recombination with the grafted side chain radicals, although secondary graft copolymerization from the grafted chain radicals is still the principal process for the growth of the surface homopolymer layer.     

Inclusion complexation of volatile chlorinated hydrocarbons in aqueous solutions of branched cyclodextrins

The inclusion complexation of five volatile chlorinated hydrocarbons, i.e., chloroform, carbon tetrachloride, trichloroethylene, tetrachloroethylene, and monochlorobenzene, with branched cyclodextrins (CDs) such as monoglucosyl--CD and monomaltosyl--CD in aqueous solutions was examined. Their inclusion complexes were found to be very water soluble and the solubilities of the chlorinated hydrocarbons in aqueous solutions increased almost linearly or gradually with increasing concentration of the branched CDs. The amounts of the chlorinated hydrocarbons included in the branched CDs were well related to their molecular size and shape. In addition, the viability of application to pollution prevention is discussed.