Trace speciation by HPLC?GF AA for tin- and leadbearing organometallic compounds,with signal increases induced by transition-metal ions

High-performance liquid chromatography coupled with graphite furnace atomic absorption spectroscopy (HPLC? GF AA) gives element-specific detection of environmental samples containing trace amounts of organotin or organolead species. The direct GF AA of organotin and organolead species is subject to errors arising primarily from loss of analyte prior to atomization, probably through the formation of refractory carbides and of compounds or complexes that are volatile at low temperatures. Examples abound in the literature of signal suppression in the GF AA of organometallic species in environmental samples, and several furnace tube modifications have been developed to overcome this suppression. Here, the analyte and a modifier are co-pipetted into a conventional furnace tube, from either a solution of analyte or an HPLC effluent. Oxides of transition metals (e.g. chromium, manganese, or tungsten) are shown to enhance both tin and lead signals, whereas chlorides do not, suggesting the low-temperature formation of relatively involatile metal oxides or volatile metal chlorides, respectively. In the absence of modifier, GF AA signal intensities decrease consecutively for equal quantities of mono-, di-, tri- and tetra-butyltin species, but are nearly equal for the first three in the presence of complexing dichromate (Cr₂O₇^2?). The lesser signal increase for tetrabutyltin indicates a dissimilar low-temperature complexation chemistry for the fully ligated neutral organometal to that for the ligated ions. similar results are demonstrated in post-column addition of a matrix modifier to effluent containing either organotin or organolead species.     

Simulation of two- and three-dimensional internal subsonic flows using a finite element method

In this paper a finite element method is presented to predict internal subsonic flows. Using a low-Mach-number approximation, the pressure is decomposed into a mean thermodynamic contribution and a dynamic fluctuation to deal with the complex role of the pressure in internal aerodynamics. A semi-implicit time integration and a finite element method with a moving mesh are described to take into account complex geometries and moving boundaries. An Uzawa algorithm accelerated by a preconditioned residual method is introduced to solve the coupled non-symmetric linear system for the velocity components and the pressure. An efficient conjugate gradient method combined with an incomplete LU preconditioning is used to solve the non-symmetric linear systems arising from the discretization. The implementation of the numerical scheme on parallel supercomputers is also discussed. Efficient algorithms for the finite element assembly phase and for the solution of linear systems are described which take advantage of the parallel architecture of the new generation of supercomputers. With this technique a global speed-up of 10 is achieved on a supercomputer with eight processors. To illustrate the capabilities of the numerical method, 2D and 3D simulations of flows in the combustion chamber of a reciprocating engine and around the combustor dome of a gas turbine engine are presented.     

Reactive oxygen species, cell growth, and taxol production of Taxus cuspidata cells immobilized on polyurethane foam

Dynamic changes in reactive oxygen species (ROS) of Taxus cuspidata cells immobilized on polyurethane foam were investigated and the relation between ROS content and taxol production was discussed. Immobilization shortened the lag period of cell growth and moderately increased H₂O₂ and O₂ ^−• contents inside the microenvironment within the first 15 d. After 20 d, excessive production of H₂O₂ and O₂ ^−• was observed accompanied by marked increases in membrane lipid peroxidation and cell membrane permeability. The taxol content of immobilized cells was fourfold that of suspended cells at d 35. The addition of exogenous H₂O₂ barely affected malondialdehyde content and cell membrane permeability but led to an obvious accumulation of taxol. It is inferred that the intracellular and extracellular H₂O₂ inside the microenvironment might be one factor promoting taxol biosynthesis under the immobilization stress.     

Preparation and characterization of polyaluminum chloride containing high content of Al13 and active chlorine

This paper introduces a new electrochemical method for preparation of polyaluminum chloride (PACl) which contains high content of Al₁₃ and active chlorine and presents integrated properties of flocculation with oxidation. E-PACl (PACl prepared by electrolysis process) samples were successfully prepared in an electrochemical reactor, which used Ti/RuO₂–TiO₂ anodes and Ti cathodes. Anode potential was the key electrochemical parameter that needed to be controlled at 1.5 V to ensure the maximal current efficiency of main reactions in electrolysis process. Analyses by ferron colorimetric method and ²⁷Al NMR spectroscopy indicated that Al₁₃ was the predominant species in the final product when total Al concentration (Al_T) was in the range of 0.1–1.5 mol/L. The amount of active chlorine was in inverse proportion to Al_T. Contents of the most active component, Al₁₃ and active chlorine could respectively reach 90.9% and 5650 mg/L with Al_T = 0.51 mol/L and basicity (B, OH/Al molar ratios) = 2.23 in the liquid product of PACl (E-PACl2). In E-PACl2, the sulfate precipitate of Al₁₃ was the unique material detected by X-ray diffraction patterns and clusters of small spheres that might be the aggregates of Al₁₃ were observed on the surface of its air-dried sample by atomic force microscopy. Results of dynamic light scattering showed that the particle size distributions of E-PACl were related with the Al species distributions and ageing time. The active chlorine in E-PACl2 performed well on disinfection of raw water.     

Enhancing the ratio of molecular ions to non-covalent compounds in the electrospray interface of LC-MS in quantitative analysis

A common problem encountered during the development of MS methods for the quantitation of small organic molecules by LC-MS is the formation of non-covalently bound species or adducts in the electrospray interface. Often the population of the molecular ion is insignificant compared to those of all other forms of the analyte produced in the electrospray, making it difficult to obtain the sensitivity required for accurate quantitation. We have investigated the effects of the following variables: orifice potential, nebulizer gas flow, temperature, solvent composition and the sample pH on the relative distributions of ions of the types MH⁺, MNa⁺, MNH₄⁺, and 2MNa⁺, where M represents a small organic molecule: BAY 11-7082 ((E)-3-[4-methylphenylsulfonyl]-2-propenenitrile). Orifice potential, solvent composition and the sample pH had the greatest influence on the relative distributions of these ions, making these parameters the most useful for optimizing methods for the quantitation of small molecules.     

钙对铝水解聚合反应及聚合铝物化特性的影响

The polyaluminum chloride containing Ca was prepared by adding Ca before and after the aluminium polymerization, respectively. The effects of Ca on the hydrolysis and polymerization of aluminum, the characteristic of aluminum species, the ζ potential and viscosity of PAC were also studied. The experimental results show that the introduction of Ca retards the formation of Al precipitates during the hydrolysis and polymerization of aluminum and increases the contents of Al_m and Al₁₃ in PAC. Aluminum species can complex with Ca to form heteronuclear hydroxo complexes, which decreases the chemical shifts of Al_m and Al₁₃ in NMR. The ζ potential and the viscosity of PAC increase with the rise of Ca/Al molar ratio. Comparing with adding Ca after the aluminium polymerization, there are much more Al-Ca heteronuclear hydroxo complexes formed by adding Ca before the polymerization, which leads to a more obvious influence of Ca/Al molar ratio on the ζ potential and the viscosity of PAC.     

Antioxidant responses to oleic acid in two-liquid-phase suspension cultures of Taxus cuspidata

Two-liquid-phase plant cell cultures employ the use of a partitioning system to redirect extracellular product into a second phase. After the addition of organic solvent, in order to understand the defense system of Taxus cuspidata cells to organic solvent in two-liquid-phase suspension cultures, we investigated cells' antioxidant metabolism. The results showed that T. cuspidata cells responded to oleic acid with oxidative bursts in both intracellular H₂O₂ and extracellular O₂ ⁻ production. Inhibition studies with diphenylene iodonium suggested that the key enzyme responsible for oxidative bursts was primarily NADPH oxidase. Investigation of the relationship between reactive oxygen species (ROS) and defense responses induced by oleic acid indicated that 4% (v/v) oleic acid increased the levels of antioxidant enzymes of superoxide dismutase, ascorbate peroxidase, and catalase and the antioxidant capacity of reduced ascorbate and glutathione. However, when oleic acid content reached a critical value (6% [v/v]), no further increase in antioxidant enzymes and antioxidant capacity was observed, indicating that the defense responses played a role in a certain range of oleic acid content, beyond which the overall ROS scavenging machinery was not induced and the peroxidation of membrane lipids emerged.     

由HRuCo_3(CO)_(12)制备的催化剂上CO加氢反应中含氧产物分布与表面酰基的关系

由HRuCo_3(CO)_(12)制备的催化剂在CO加氢反应中,若在初始阶段或温度较低的条件下,含氧产物大部分是甲醇;若增加反应时间或提高反应温度,C_2含氧化合物则是主要产物。原位红外光谱揭示了甲酰基和乙酰基分别是形成甲醇和C_2含氧化合物的中间体,而且乙酰基来自甲酰基与甲基的相互工作用。     

处理条件对Mo/HZSM-5催化剂结构及性能的影响

使用付立叶变换红外光谱和固体高分辨核磁技术，考察了在不同处理条件下，甲烷无氧芳构化催化剂Ｍｏ／ＨＺＳＭ５分子筛骨架结构的变化情况．结果显示，较高的焙烧温度和较高的预处理温度，都会造成催化剂中担载的钼物种对分子筛骨架铝的严重抽提，特别是在钼物种含量较高时，这种情况更明显．以不同担体及不同钼物种构成的前驱态催化剂的催化反应评价结果表明，以微晶状态存在的ＭｏＯ３和与担体间以相对较弱作用力存在的高分散钼物种，在反应过程中被活化成具有催化活性钼物种的几率更大；而晶相状态的Ａｌ２（ＭｏＯ４）３以及与载体间存在较强相互作用力的钼物种，在甲烷无氧芳构化过程中不起主要催化活性作用．计算得出，甲烷无氧脱氢芳构化反应的表观活化能为８９．８ｋＪ／ｍｏｌ．     

Haloaldehyde polymers,XLIX: Analysis of linear bornyl oxide initiated,acetate endcapped chloral oligomers by potassium ionization of desorbed species mass spectrometry

Linear chloral oligomers initiated with lithium bornyl oxide and acetate endcapped were analyzed by potassium ionization of desorbed species (K⁺ IDS) mass spectrometry. Using this technique we observed ions resulting from the [unimer]K⁺ with a mass of 381 daltons, to the [hexamer]K⁺ with a mass of 1 119 daltons. Furthermore, analysis of the isotope pattern supported our structural assignment. The individual lower oligomers were also investigated by GC and NMR spectroscopy.Previous paper in this series: Haloaldehyde Polymers XL VIII. W. J. Simonsick Jr., K. Hatada, Fu Xi, and O. Vogl [27]