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951.
Methane conversion in the presence of oxygen under low-temperature radio frequency (RF) plasma was investigated. The experiment results indicated that the following four factors, i.e., discharge voltage, discharge area, O2/CH4 molar ratio and total gas flowrate, affected remarkably the reaction performance. The optimum reaction conditions of methane conversion in the presence of O2 under RF plasma are as follows: discharge voltage 1050 V, discharge area 989.1mm2, O2/CH4 molar ratio 1/10 and total gas flowrate 200 ml/min. A methane conversion of 91% could be reached under the optimum conditions. Oxygen is good for the breaking of C--H bonds and also acts as a sort of thinner. According to the low-temperature plasma characteristics, the macroscopic kinetics model of methane conversion in the presence of O2 under radio frequency plasma was studied. 相似文献
952.
Xue‐Mei Wang Xin‐Zhen Du Hong‐Hong Rao Xiao‐Quan Lu 《Journal of separation science》2010,33(20):3239-3244
A novel mesoporous‐coated stainless steel wire microextraction coupled with the HPLC procedure for quantification of four polycyclic aromatic hydrocarbons in water has been developed, based on the sorption of target analytes on a selectively adsorptive fiber and subsequent desorption of analytes directly into HPLC. Phenyl‐functionalized mesoporous materials (Ph‐SBA‐15) were synthesized and coated on the surfaces of a stainless steel wire. Due to the high porosity and large surface area of the Ph‐SBA‐15, high extraction efficiency is expected. The influence of various parameters on polycyclic aromatic hydrocarbons extraction efficiency were thoroughly studied and optimized (such as the extraction temperature, the extraction time, the desorption time, the stirring rate and the ionic strength of samples). The results showed that each compound for the analysis of real water samples was tested under optimal conditions with the linearity ranging from 1.02×10?3 to 200 μg/ L and the detection limits were found from 0.32 to 2.44 ng/ L, respectively. The RSD of the new method was smaller than 4.10%. 相似文献
953.
A novel chemically bonded graphene oxide/fused-silica fiber was prepared and applied in solid-phase microextraction of six polycyclic aromatic hydrocarbons from water samples coupled with gas chromatography. It exhibited high extraction efficiency and excellent stability. Effects of extraction time, extraction temperature, ionic strength, stirring rate and desorption conditions were investigated and optimized in our work. Detection limits to the six polycyclic aromatic hydrocarbons were less than 0.08 μg/L, and their calibration curves were all linear (R(2)≥0.9954) in the range from 0.05 to 200 μg/L. Single fiber repeatability and fiber-to-fiber reproducibility were less than 6.13 and 15.87%, respectively. This novel fiber was then utilized to analyze two real water samples from the Yellow River and local waterworks, and the recoveries of samples spiked at 1 and 10 μg/L ranged from 84.48 to 118.24%. Compared with other coating materials, this graphene oxide-coated fiber showed many advantages: wide linear range, low detection limit, and good stability in acid, alkali, organic solutions and at high temperature. 相似文献
954.
Ismail Anıl Naciye Öztürk Omar Alagha Pınar Ergenekon 《Journal of separation science》2012,35(24):3561-3568
This article introduces a simple, rapid, and reliable solid‐phase microextraction (SPME) method coupled with GC‐MS for the quantitative determination of 16 polycyclic aromatic hydrocarbons in water. In this study, the Taguchi experimental design was used to optimize extraction conditions of polycyclic aromatic hydrocarbons using SPME method to obtain highly enriched analytes. Consequently, quantitative determination of polycyclic aromatic hydrocarbons in water was achieved by GC‐MS technique. The selected parameters affecting enrichment of polycyclic aromatic hydrocarbons were sample extraction time, stirring speed, temperature, ionic strength, and pH. The study revealed that optimal operating conditions were found to be 90‐min extraction time, 1400 rpm stirring speed, and 60°C sample temperature. The effect of ionic strength and pH were shown to be insignificant. Optimized conditions were also reevaluated by placing the 16 polycyclic aromatic hydrocarbons into several subgroups based on their molecular weight. The extraction efficiency of polycyclic aromatic hydrocarbons with low molecular weight was shown to be a function of only the extracting temperature. Satisfactory results were obtained for linearity (0.983–0.999), detection limits (2.67–18.02 ng/L), accuracy (71.2–99.3%), and precision (4.3–13.5%). The optimum conditions reported by other design approaches were evaluated and generalized optimum conditions were suggested. 相似文献
955.
The weakest bound potential method was proposed to estimate the ionization potential (IP) of polyhalogenated methanes, that is, the model IP = aχve + bPEIfi + c was developed, in which χve is molecular electronegativity calculated by valence electrons equilibration method, and polarizability effect index (PEI)fi is the influence of polarizability effect. The result indicates that the model is reasonable and effective to predict the IP for polyhalogenated methanes. Besides, the quantum chemistry method, the MOPAC AM1 method, and the density functional theory (B3LYP) method were employed to calculate the IP values of the same polyhalogenated methanes, and those results were less than that of the weakest bound potential method. Furthermore, the experimental values of 67 polyhalogenated hydrocarbons were correlated with the parameters χve and PEIfi. The regression results show a good correlation (R = 0.988), and the average absolute error between the experimental values and the calculated values is only 0.10 eV. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
956.
Brian Halton 《Tetrahedron letters》2006,47(7):1077-1079
Upon flash vacuum thermolysis at 750 °C fluorenylidenecyclopropa[b]naphthalene (1) undergoes opening of the three-membered ring and rearrangement to give a range of C24H14 polycyclic aromatic hydrocarbons. Dibenz[e.l]- and -[e.k]acephenanthrylene (7) and (12), respectively, have been identified while the plausible naphth[1,2-e]- and [2,3-e]acephenanthrylenes (9) and (14) were not detected. With diphenylmethylidenecyclopropa[b]naphthalene (2) cyclodehydrogenation and rearrangement also provide C24H14 polycycles; dibenz[e.k]acephenanthrylene (12) is identified and dibenz[a.e]aceanthrylene (15) is a proposed product. 相似文献
957.
958.
959.
For environmental analyses, a high-performance and powerful preconcentration system exceeding 1×107-fold was developed that was composed of a blue cotton method (solid extraction method)/homogeneous liquid–liquid extraction method/on-line concentration method for capillary electrophoresis (CE). This system was named the “triplex concentration system” and it was achieved by finding a new phase-separation phenomenon (homogeneous liquid–liquid extraction) from a water-miscible organic solvent. Parts per trillion levels of polycyclic aromatic hydrocarbons (PAHs) were used as model analytical targets in this study. With the proposed method, 20-L levels of environmental water could be preconcentrated up to 1×107-fold within a maximum of 1 h. The parts per trillion levels of PAHs were easily determined even using UV/CE, which has a serious sensitivity problem, and the detection limit of benzo[a]pyrene was 3.60 ppt. This system was also used as a practical monitoring method for the Miyata River (in Japan). 相似文献
960.
Herbert P Silva AL João MJ Santos L Alves A 《Analytical and bioanalytical chemistry》2006,386(2):324-331
The present work was focused on the development of a simple method aimed at the determination of 12 polycyclic aromatic hydrocarbons
(PAHs) and 15 polychlorinated biphenyls (PCBs) in landfill leachates and sediments by adapting a domestic microwave oven to
perform microwave-assisted headspace solid-phase microextraction (MA-HS-SPME) followed by gas chromatographic separation and
tandem mass spectrometric detection. Good linearity was observed within the concentration range studied; detection limits
ranged from 0.1 ng/l to 7 ng/l for PCBs and from 5 ng/l to 926 ng/l for PAHs. Concerning precision, the relative standard
deviations obtained were, on average for the leachate and sediment samples analysed, 18% for PCBs and 20% for PAHs. Average
recovery values were 37% and 76% for PCBs, and 58% and 48% for PAHs, respectively, for the leachate and reference sediment
studied. The method allows the determination of PAHs and PCBs in landfill leachates and sediments, avoiding clean-up steps
and the consumption of organic solvents. 相似文献