Electrical wiring of Pseudomonas putida and Pseudomonas fluorescens with osmium redox polymers

Two different flexible osmium redox polymers; poly(1-vinylimidazole)12-[Os-(4,4'-dimethyl-2,2'-di'pyridyl)2Cl2](2+/+) (osmium redox polymer I) and poly(vinylpyridine)-[Os-(N,N'-methylated-2,2'-biimidazole)3](2+/3+) (osmium redox polymer II) were investigated for their ability to efficiently "wire" Pseudomonas putida ATCC 126633 and Pseudomonas fluorescens (P. putida DSM 6521), which are well-known phenol degrading organisms, when entrapped onto cysteamine modified gold electrodes. The two Os-polymers differ in redox potential and the length of the side chains, where the Os(2+/3+)-functionalities are located. The bacterial cells were adapted to grow in the presence of phenol as the sole source of organic carbon. The performance of the redox polymers as mediators was investigated for making microbial sensors. The analytical characteristics of the microbial sensors were evaluated for determination of catechol, phenol and glucose as substrates in both batch analysis and flow analysis mode.     

负载于HZSM-5上的CuO-ZnO-Al2O3纳米粒子：尿素－硝酸盐燃烧合成和理化表征

用尿素-硝酸盐燃烧法制备了一系列的负载于HZSM-5上的CuO-ZnO-Al2O3纳米复合材料(CZA/HZSM-5)。研究了燃料与氧化物的比率对所合成的复合材料的理化性质的影响。用TGA/DTG,FTIR和XRD等研究了尿素-硝酸盐凝胶的热分解和煅烧粉体的相演变过程。FESEM结果表明在燃烧过程中燃料的用量对CZA/HZSM-5的性质有重大影响。CuO和ZnO的晶粒首先随尿素量的增加而增大,然后随尿素量的增加而减小。CuO和ZnO的相对结晶度随燃料量的增加表现为非单调趋势。随着燃料与硝酸盐的比率的增加,CZA/HZSM-5不仅形貌变得超细和均一,而且表面孔隙率也显著增加。FTIR结果表明HZSM-5的结构甚至在负载了CuO-ZnO-Al2O3纳米粒子后也未被破坏,而且在CuO和ZnO与HZSM-5之间还有表面的键合。TGA/DTG结果指出燃烧合成法是一种由若干过程组合起来的方法,例如前驱体的热分解和前驱体间的放热反应等。另外,提出了CuO-ZnO-Al2O3负载在HZSM-5上的生成机理。     

Development of Flow Injection Spectrofluorimetric Detection System for the Determination of Homocysteine

In this work, a new simple and sensitive flow injection method is developed for the determination of homocysteine with spectrofluorimetric detection technique. This method is based on the oxidation of homocysteine with Tl (III) in acidic media, producing fluorescence reagent, TlCl₃^2- (λ_ex = 237 nm, λ_em = 419 nm). The effects of chemical parameters (including pH of the solutions, the buffer, Tl (III) and potassium chloride concentrations), instrumental parameters (such as flow rate of the solutions, reaction coil length, and sample loop volume) and temperature on the fluorescence intensity as an analytical signal are studied and optimized. In the optimum conditions of the above variables, homocysteine can be determined in the range 4.0 × 10^-7–40.0 × 10^-6 M with the LDR from 4.0 × 10^-7 to 25.0 × 10^-6 M. The detection limit (with S/N = 3) is 6.0 × 10^-8 M of homocysteine and precision for the injection of 5.0, 10.0 and 15.0 μM of homocysteine are 0.8%, 1.5% and 2.5% (n = 10) respectively. The rate of analysis is 90 samples per hour. The influence of potential interfering substances, including amino acids and carbohydrates is also studied. The proposed method has been successfully used for the determination of homocysteine in the real sample (blood serum and tap water) matrix.     

Upscaled Unstructured Computational Grids for Efficient Simulation of Flow in Fractured Porous Media

Discrete fracture modeling (DFM) is currently the most promising approach for modeling of naturally fractured reservoirs and simulation of multiphase fluid flow therein. In contrast with the classical double-porosity/double permeability models, in the DFM approach all the interactions and fluid flow in and between the fractures and within the matrix are modeled in a unified manner, using the same computational grid. There is no need for computing the shape factors, which are crucial to the accuracy of the double-porosity models. We have exploited this concept in order to develop a new method for the generation of unstructured computational grids. In the new approach the geological model (GM) of the reservoir is first generated, using square or cubic grid blocks. The GM is then upscaled using a method based on the multiresolution wavelet transformations that we recently developed. The upscaled grid contains a distribution of the square or cubic blocks of various sizes. A map of the blocks’ centers is then used with an optimized Delauney triangulation method and the advancing-front technique, in order to generate the final unstructured triangulated grid suitable for use in any general reservoir simulator with any number of fluid phases. The new method also includes an algorithm for generating fractures that, contrary to the previous methods, does not require modifying their paths due to the complexities that may arise in spatial distribution of the grid blocks. It also includes an effective partitioning of the simulation domain that results in large savings in the computation times. The speed-up in the computations with the new upscaled unstructured grid is about three orders of magnitude over that for the initial GM. Simulation of waterflooding indicates that the agreement between the results obtained with the GM and the upscaled unstructured grid is excellent. The method is equally applicable to the simulations of multiphase flow in unfractured, but highly heterogeneous, reservoirs.     

Flow injection analysis of nitrite by gas phase molecular absorption UV spectrophotometry

A flow injection method on the basis of gas phase molecular absorption is described for the determination of nitrite in the aqueous solution. 200 mul of nitrite solution is introduced into a carrier stream of distilled water. The carrier stream containing nitrite zone is reacted with a stream of hydrochloric acid (2 M). The stream is then segmented by O(2) gas. The produced gaseous products are purged into the O(2) segments, react with O(2) and are carried toward the gas-liquid separator. The gaseous phase is separated from the liquid stream by the use of home-made gas-liquid separator and then is swept into a home-made flow cell. The absorbance of gaseous phase is measured at 205 nm using a UV/VIS spectrophotometer. Under selected conditions, two linear ranges, up to 1000 mug ml(-1) and 1000-2000 mug ml(-1) of nitrite were obtained. The limit of detection was 7.5 mug ml(-1) NO(2)(-). The relative standard deviations of repeated measurements of 100 and 500 mug ml(-1) NO(2)(-) were 3.7 and 1.0%, respectively. Up to 30 samples h(-1) can be analyzed. Interferences in the proposed method were few and were readily overcome. The proposed method was successfully applied to the determination of nitrite in the spiked water samples, a number of meat products and urine.     

A Modified Z-Type Flow-through Cell for Optical, Electrochemical, and Optoelectrochemical Flow Injection Analysis Measurements

The design and construction of a modified Z-type flow-through cell that can be used for optical, electrochemical, and optoelectrochemical measurements are reported. In optical analysis, the proposed flow cell is placed in the light path of a spectrophotometer and worked as a commercial Z-type optical flow cell. In electrochemical analysis, the working and auxiliary electrodes are two platinum sheets placed at both ends of the cell cavity; the cell cavity is enclosed by two glass windows. The reference electrode is a saturated calomel electrode placed downstream in an overflow tube. The performance of the proposed electrochemical flow cell was studied by analysis of hexacyanoferrate solution as an electroactive species. In optoelectrochemical analysis, the proposed flow cell is operated optically and electrochemically, simultaneously. The flow cell is placed in the light path of a spectrophotometer, constant potential is applied to the electrodes, and the optical and electrochemical signals are recorded simultaneously by the use of two recorders.     

Rapid kinetic determination of silver (I), using in-cuvette mixing and computerized data acquisition

 The determination of silver(I) based on its catalytic effect on the oxidation of indigo carmine with hexacyanoferrate(III) is described. The reaction is monitored spectrophotometrically by means of a home-made rapid system with computer data acquisition. The decrease in absorbance of indigo carmine at 612 nm, pH 6 and at a fixed concentration of hexacyanoferrate(III) and indigo carmine is proportional to the concentration of Ag(I). The acquired data based on the initial rate and fixed time are processed. Up to 100.0 μg/ml of silver are determined. The limit of detection and average relative standard deviation are 0.13 μg/ml and 1.9%, respectively. The effect of foreign ions on the determination of silver is also discussed. The proposed method is applied to the determination of Ag(I) in expired photographic film. Received: 17 June 1996 / Revised: 26 July 1996 / Accepted: 2 August 1996