Analysis of coal tar and petroleum pitches by computerized pattern recognition

Pyrolysis gas chromatography (P/GC) has been successful in differentiating coal tar pitches which are used in the manufacture of high temperature graphite materials [1,2]. In the present study, coal tar and petroleum pitches received from five suppliers were readily differentiated using three distinct methods of polymer analysis: dynamic headspace and pyrolysis gas chromatography mass spectrometry (DH/GC/MS and P/GC/MS, [3]), and pyrolysis mass spectrometry (P/MS, [4,5]). All of these methods are appropriate for the analysis and pattern recognition study of coal and petroleum products; however, methods which incorporate GC usually necessitate long analysis times and are subject to problems associated with gas chromatographic reproducibility (e.g. active sites [6], and nonconstant retention times). As a fingerprint analysis method, P/MS is rapid and ideally suited to computerized pattern recognition study of pitches due to the simple format of P/MS data (computer tabulation of normalized intensities versus masses); whereas, in the present study, the normalized peak area versus retention time date from DH/GC/MS and P/GC/MS analyses were not suitable for direct input to a computerized pattern recognition analysis program, (due to non-constant retention times and improper data format). One limitation is that P/MS does not provide positive identification of thermally evolved products (as can DH/GC/MS and P/GC/MS) due to the complexity of the spectra of a mixture of compounds produced by P/MS. Within the limits of the commercial instrumentation and computer programs used in this study, a combination of all three techniques provided the greatest capability for the differentiation of the five coal tar and petroleum based pitches studied.     

Orientational sampling and rigid-body minimization in molecular docking revisited: On-the-fly optimization and degeneracy removal

Summary Strategies for computational association of molecular components entail a compromise between configurational exploration and accurate evaluation. Following the work of Meng et al. [Proteins, 17 (1993) 266], we investigate issues related to sampling and optimization in molecular docking within the context of the DOCK program. An extensive analysis of diverse sampling conditions for six receptor-ligand complexes has enabled us to evaluate the tractability and utility of on-the-fly force-field score minimization, as well as the method for configurational exploration. We find that the sampling scheme in DOCK is extremely robust in its ability to produce configurations near to those experimentally observed. Furthermore, despite the heavy resource demands of refinement, the incorporation of a rigid-body, grid-based simplex minimizer directly into the docking process results in a docking strategy that is more efficient at retrieving experimentally observed configurations than docking in the absence of optimization. We investigate the capacity for further performance enhancement by implementing a degeneracy checking protocol aimed at circumventing redundant optimizations of geometrically similar orientations. Finally, we present methods that assist in the selection of sampling levels appropriate to desired result quality and available computational resources.     

中草药中铁锌钙的悬浮液进样-火焰原子吸收光谱法测定

将悬浮液进样技术应用于火焰原子吸收光谱法, 建立了中草药中微量元素的快速分析新方法。将样品粉碎、悬浮在琼脂胶体中制成悬浮液; 取适量样品悬浮液配制成试液, 喷入空气－ 乙炔火焰, 用标准加入法测定。 用该法成功地测定了当归、川芎及川乌中的铁、锌、钙, 测定结果与灰化法一致, 方法简便、快速、准确。     

Coupling of thermal desorption in modified closeable sampling columns with wide-bore capillary gas chromatography and mass spectrometric detection

In contrast to usability of Curie-point pyrolysis at 700°C directly attached to gas chromatography-mass spectrometry (GC-MS) for determination of organic wood preservatives in waste wood samples the investigation method reported here consists of thermal desorption at temperatures about 260°C in connection with GC-MS for peak identification or GC with flame ionization detection for quantitative analyses. So-called “modified closeable sampling columns” are used as batch-reactor in thermal desorption experiments. Desorbed vapours can be introduced on capillary columns without sample discrimination and without a disturbing lost of resolution. In this manner a lot of individual polycyclic aromatic hydrocarbons were determinated in waste wood samples, especially in railway sleepers.     

Detection of ethanol in human body fluids by headspace solid-phase micro extraction (SPME)/capillary gas chromatography

Summary Ethanol has been found extractable from human whole blood and urine samples by headspace solid-phase micro extraction (SPME) with a Carbowax/divinylbenzene-coated fiber. After heating a vial containing the body fluid sample with ethanol, and isobutanol as internal standard (IS) at 70°C in the presence of (NH₄)₂SO₄, a Carbowax/divinylbenzene-coated SPME fiber was exposed in the headspace of the vial to allow adsorption of the compounds. The fiber needle was then injected into a middle-bore capillary gas chromatography (GC) port. The headspace SPME-GC gave intense peaks for both compounds; a small amount of background noises appeared, but did not interfere with the detection of the compounds. Recoveries of ethanol and IS were 0.049 and 0.026% for whole blood, respectively, and 0.054 and 0.085% for urine, respectively. The calibration curves for ethanol showed excellent linearity in the range of 80–5000 mg L^–1 for whole blood and 40–5000 mg L^–1 for urine; the detection limits for both samples were 20 and 10 mg L^–1, respectively. The data on actual determination of ethanol after the drinking of beer are also presented for two subjects.     

Synthesis of Highly Porous Organic/Inorganic Hybrids by Ambient Pressure Sol-Gel Processing

This paper reports the synthesis of highly porous organic/inorganic hybrids by a two-step acid-base catalyzed sol-gel process and ambient pressure drying. In the method organic and inorganic precursors are copolymerized so as to incorporate organic ligands into the solid network. The two-step acid-base catalyzed process was used to prevent phase segregation during the hydrolysis and co-condensation of organic and inorganic precursors. The organic ligands incorporated into the solid gel network modify the surface chemistry. Thus, the wetting angle is significantly increased so that the collapse of the gel network is greatly reduced upon the removal of pore fluid during drying. Organic/inorganic hybrids with BET surface areas above 1250 m2/g, porosities above 75% and pore sizes of 8 nm have been synthesized.     

Emission of Sulphur Dioxide During Thermal Treatment of Fossil Fuels

The dynamics of SO₂ emission during thermooxidation of Estonian oil shale, its semicoke, different samples of coal and their mixtures, as well as the influence of Estonian oil shale ash addition (for modelling the CFBC process) on the dynamics were studied. The experiments were carried out with thermogravimetric equipment under dynamic heating conditions (5 K min^-1) in the atmosphere of dried air, with simultaneous gastitrimetric EGA. It was established that SO₂ emission from the fuels started at 200-320°C. Depending on the form of sulphur (organic, pyritic, sulphate), the emission took place in two or three steps, and continued up to 580-650°C, during which 35-75% of the total sulphur was emitted into the gaseous phase. Regulating the mole ratio of free CaO/S in the mixtures of fuels with oil shale ash addition the emission of SO₂ ceased abruptly at 460-540°C and it was limited to the level of 7-30%. This revised version was published online in August 2006 with corrections to the Cover Date.     

Adaptive umbrella sampling of the potential energy: modified updating procedure of the umbrella potential and application to peptide folding

Adaptive umbrella sampling of the potential energy is used as a search method to determine the structures and thermodynamics of peptides in solution. It leads to uniform sampling of the potential energy, so as to combine sampling of low-energy conformations that dominate the properties of the system at room temperature with sampling of high-energy conformations that are important for transitions between different minima. A modification of the procedure for updating the umbrella potential is introduced to increase the number of transitions between folded and unfolded conformations. The method does not depend on assumptions about the geometry of the native state. Two peptides with 12 and 13 residues, respectively, are studied using the CHARMM polar-hydrogen energy function and the analytical continuum solvent potential for treatment of solvation. In the original adaptive umbrella sampling simulations of the two peptides, two and six transitions occur between folded and unfolded conformations, respectively, over a simulation time of 10 ns. The modification increases the number of transitions to 6 and 12, respectively, in the same simulation time. The precision of estimates of the average effective energy of the system as a function of temperature and of the contributions to the average effective energy of folded conformations obtained with the adaptive methods is discussed. Received: 11 July 1998 / Accepted: 22 September 1998 / Published online: 17 December 1998     

粒状物质的微观均匀度及其对取样误差的影响分析

研究物质的取样属性与以取样误差之间的关系是分析化学取样学的重要内容。从微观角度探讨了物质的理论性质及其对取样误差的影响。以碳化硅为例,考察了粒度分布、组分随粒度的变化以及均匀度因子等,分析了取样误差的来源。首次通过粒度分级成功地对碳化硅进行了分层,并对分层取样和随机取样的误差进行了分析和讨论,为制定合理的取样方案提供了有利的依据。本文的研究方法可适用于所有粒状物质的取样,同时也为分析化学取样学的深     

分层性物质的组合取样误差与份样数目之间的关系及其Monte Carlo模拟

本文从理论上研究了分层性物质的组合取样误差与份样数目之间的定量关系,表明份样数目与组合取样相对标准偏差的平方之积为一常数,称为组合取样常数,它与Ｉｎｇａｍ ｅｌｌｓ 和Ｓｗ ｉｔｚｅｒ 提出的取样常数是相似的,表示６８％ 置信度下组合取样的相对标准偏差达到１％ 时的份样数目。应用Ｍｏｎｔｅ Ｃａｒｌｏ 模拟技术对该理论进行了验证,结果令人满意。