离子选择电极—流动注射分析法动力学测定葡萄糖存在下的果糖

本文将离子电极与流动注射分析相结合，利用３０℃下，在强碱性介质中，果糖和葡萄糖与２，４－二硝基酚钠反应速度明显差异，动力学测定了葡萄糖存在下果糖的含量。自制了２，４－二硝基酚电极作为动力学电位测定用的工作电极。本法测定果糖的范围为０．０２～１．００ｍｏｌ／Ｌ，其ＲＳＤ为４．０％～４．９％，ＲＥ为１．０～５．０％；当Ｃ葡／Ｃ果≤３倍时，葡萄糖的干扰不超过５％；本法也曾成功地用于果葡萄浆测定，其ＲＳＤ     

PVC膜对硝基酚离子选择电极对三溴酚离子的响应性能及在工业废水分析中的应用

介绍了以碱性染料乙基紫阳离子EV~+(Ethyl·Violet)与对硝基酚阴离子NPO~-(Nitrophenol)离子缔合物EV~+NPO~-为电活性物质的PVC膜(Polyvinyl Chloride)对硝基酚离子选择电极对三溴酚离子TBPO~-(Tribromophenol)的响应性能的测试方法以及电极响应的特性参数,并利用此电极对工业废水中酚的总含量进行测定。测试结果与容量方法及比色法结果比较,表明此方法具有较高的准确度。     

PC膜二硝基苯酚离子选择电极的研制和应用

二硝基酚是化学工业的重要中间体。一般用比色法测定,但不宜用于浑浊试样。Selig曾试图用1,2,4,6-四苯基吡啶醋酸盐作滴定剂,电位滴定二硝基苯酚,未获成功。我们在前文基础上采用2,4-二硝基苯酚的四(十二烷基)铵或三(十二烷基)十六烷基铵离子对缔合物为电极活性物质,研制了PVC膜二硝基苯酚离子选择电极(DNP电极)。线性响应范围1×10~(-2)～1×10~(-5)M,斜率59mV。用它作指示电极,三辛基甲基氯化铵为滴定剂,以电位     

用氟离子选择电极测定包头矿中氟

虽然氟离子选择电极在分析中已获得广泛的应用,但是用该电极电位法测定包头矿中氟的结果,人们尚有疑义。本文研究了酸溶蒸馏分离-氟离子电极法测定氟时,稀土元素对氟的回收率的影响和几种常用掩蔽体系对铝(Ⅲ)的掩蔽效果及其试验条件。拟定了碱熔试样,以氟离子电极法测定包头矿中氟的方法,並对     

痕量硝基酚的反相高效液相色谱电化学检测

本文以甲醇与０．０３ｍｏｌ／Ｌ邻苯二甲酸氢钾缓冲液为淋洗液，采用安培型电化学检测，实现了２－硝基苯酚，３－硝基苯酚，４－硝基苯酚及２，４－二硝基苯酚和２，６－０二硝基苯酚等五种酚类化合物于Ｐｅｒｋｉｎ－Ｅｌｍｅｒ Ｎｕｃｌｅｏｓｉｌ Ｃ８柱上反相高效液相色谱的分离及在Ｅ＝＋１．２Ｖ时于玻碳电极上的同时检测。     

碳纳米管复合聚对氨基吡啶修饰电极伏安法同时测定硝基酚异构体的研究

利用导电聚合物的分子识别性和碳纳米管奇特的物理化学性质, 制备了碳纳米管复合聚对氨基吡啶(SWNTs/POAP)修饰电极, 研究了邻、间、对硝基酚异构体同时在该电极上的电化学响应. 实验结果表明, 邻、间、对硝基酚异构体在SWNTs/POAP纳米电极界面具有不同的构象, 其氧化峰电位能够完全分开, 并能显著地提高电化学测定的灵敏度. 文中的SWNTs/POAP纳米电极制备简单方便, 可用于硝基酚位置异构体的同时电化学量测.     

AM1方法研究二硝基重氮酚异构化及热消除反应

ＡＭ１方法研究二硝基重氮酚异构化及热消除反应李永红，王，洪三国肖鹤鸣（江西师范大学化学系，南昌，３３００２７）（南京理工大学化学系）关键词二硝基重氮酚，异构化，热消除，过渡态二硝基重氮酚（ＤＤＮＰ）具有良好的性能，是重要的起爆炸药［１］．迄今为止，对...     

麝香草酚比色法测定硫酸镍中硝酸根

硫酸镍中硝酸根,是直接影响电镀工艺的重要因素之一。因此,建立一个测定硫酸镍中硝酸根的方法是必要的。硝酸根的测定,目前使用的方法有酚二磺酸法、麝香草酚法、亚铁法、离子选择电极法等。这些方法,各有优缺点,就灵敏度、安全性和操作繁简来说,以麝香草酚比色法为佳。本文在前人工作基础上,采用麝香草酚作为硝酸根的显色剂,就操作条件进行了试验,拟定了切实可行的测定硝酸根的方法。     

异构体化合物的电化学传感器检测进展

综述了电化学传感器在分离和检测异构体化合物方面的研究进展.在位置异构体方面,介绍了碳纳米管修饰电极、碳纳米管复合修饰电极、表面活性剂增敏下的玻碳电极对酚类异构体的检测研究(包括萘酚、硝基酚、二硝基酚、苯二酚);在立体异构体方面,重点介绍了碳糊修饰电极、酶修饰电极、手性膜电极、免疫传感器的制备及其在氨基酸对映体检测中的应用,并展望了该研究领域的发展前景.     

乌鸡白凤丸铅含量的离子选择电极法测定

采用离子选择电极法测定乌鸡白凤丸中铅的含量，方法的回收率１０１．３２％，变异系数０．８７％。     

Regioselective protection of xylose for efficient synthesis of arabino-α-1,3-xylosides

We reported here an efficient regioselective protection strategy for xylose with two-step successive protections on 4- and 2-OH. This method enables the expeditious preparation of various xylose building blocks (3a–c, 5, 6). The rapid selective 2,4-protection especially facilitates the synthesis of 3-substituted xyloside structures. By this approach, typical arabino-α-1,3-xyloside disaccharide and trisaccharide, as fragment structure units from arabinoxylans, have been successfully synthesized.     

Electrochemically Deposited Polymer‐Coated Gold Electrodes Selective for 2,4‐Dichlorophenoxyacetic Acid

Electropolymerized membranes on gold electrodes doped with 2,4‐dichlorophenoxyacetic acid (2,4‐D) were prepared from a solution containing resorcinol, o‐phenylenediamine and 2,4‐D. Fourier Transform Infrared (FTIR) spectroscopy was used to evaluate the incorporation and interaction of 2,4‐D with the polymer matrix prior to and after the sensing experiments. The FTIR data indicate that 2,4‐D does not leach appreciably from the polymer matrix under experimental conditions employed for the sensing studies. The electrochemical current response for 2,4‐D is compared for the doped polymer‐coated and control polymer‐coated electrode. The response of the doped polymer‐electrode was dependent on increasing concentrations of 2,4‐D and 2,4‐dichlorophenol while unresponsive to benzoic acid.     

Energetics of xylose decomposition as determined using quantum mechanics modeling

The decomposition of xylose has been studied using quantum mechanical calculations supported by NMR data. Proposed mechanisms for the decomposition of xylose have been investigated by obtaining the structures and energies of transition states and products. The intent of this study was to understand the experimentally observed formation of furfural and formic acid that occurs during the decomposition of xylose in mildly hot acidic solutions. A mechanism of furfural formation involving the opening of the pyranose ring and subsequent dehydration of the aldose was compared to a direct intramolecular rearrangement of the protonated pyranose. Energies were determined using CBS-QB3, and it was shown that the barriers for dehydration of the aldose were high compared to intramolecular rearrangement. This result suggests that the latter mechanism is a more likely mechanism for furfural formation. The intramolecular rearrangement step results from protonation of xylose at the O2 hydroxyl group. In addition, it has been shown that formic acid formation is a likely result of the protonation of xylose at the O3 hydroxyl group. Finally, solvation of xylose decomposition was studied by calculating energy barriers for xylose in selected water clusters. The mechanisms proposed here were supported in part by 13C-labeling studies using NMR.     

Spectroscopic and Electrochemical Characterization of Iron(II) and 2,4-Dinitrotoluene

The objective of this work was the development of reliable methods to determine 2,4-dinitrotoluene, a precursor to explosives. A complex between Fe(II) ion and 2,4-dinitrotoluene was formed in solution and characterized by ultraviolet-visible absorption spectroscopy using Job’s plots and attenuated total reflection-Fourier transform infrared spectroscopy. Surface modification of glassy carbon electrodes were performed with iron nanoparticles via electrochemical reduction of iron(II). The modified electrode was employed for the determination of 2,4-dinitrotoluene. Scanning electron micrographs showed that the iron nanoparticles were incorporated on the surface of glassy carbon electrode. The electrochemical determination of 2,4-dinitrotoluene was performed by cyclic voltammetry using the modified electrode. The iron modified electrode produced larger reduction currents than the unmodified electrode for the same concentration of 2,4-dinitrotoluene. Concentrations of 2,4-dinitrotoluene as low as 10 parts per billion were determined using the modified electrode.     

A new kinetic approach to the fermentation of multisubstrate complex media

Ethanol production from natural complex media has been studied in this work. A new kinetic approach is presented for two-substrate media, such as hardwood hemicellulose hydrolysate, which predominantly consists of a mixture of xylose and glucose. It has been founded on the supposition that the whole ethanol production and biomass growth can be subdivided into two separated components imputable to glucose and xylose consumptions, respectively. A model describing the continuous fermentation in CSTR byPachysolen tannophilus has been also presented, and experimentally verified; it takes into account the different substrate consumption rates of these sugars contained in both natural and synthetic complex media.     

2-Deoxyglucose as a selective agent for derepressed mutants of Pichia stipitis

The glucose analog 2-deoxyglucose (2-DOG) has been used to obtain mutants depressed for pentose metabolism. Some researchers have used 2-DOG alone whereas others have used it in the presence of a glucose-repressible carbon source. We examined both methods and screened mutant strains for improved use of xylose in the presence of glucose. Pichia stipitis mutants selected for growth on d-xylose in the presence of 2-DOG used xylose from a 1∶1 glucose:xylose mixture more rapidly than did their parents. One of these mutants, FPL-DX26, completely consumed xylose in the presence of glucose and produced 33g/L ethanol in 45h from 80 g/L of this sugar mixture. Mutants selected for growth on 2-DOG alone did not show significant improvement. Selection for growth on d-xylose in the presence of 2-DOG has been useful in developing parental strains for further genetic manipulation. The Forest Products Laboratory is maintained in cooperation with the University of Wisconsin-Madison. This article was prepared by U.S. Goverment employees on official time, and it is therefore in the public domain and not subject to copyright.     

Effect of Fermentation Conditions on the Flocculation of Recombinant Saccharomyces cerevisiae Capable of Co-fermenting Glucose and Xylose

Flocculation is a desirable property in industrial yeasts and is particularly important in the fuel ethanol industry because it provides a simple and cost-free way to separate yeast cells from fermentation products. In the present study, the effect of pH and lignocellulose-derived sugars on yeast flocculation was investigated using a flocculent Saccharomyces cerevisiae, MA-R4, which has been recombinantly engineered to simultaneously co-ferment glucose and xylose to ethanol with high productivity. The flocculation level of MA-R4 dramatically decreased at pH values below 3.0 during co-fermentation of glucose and xylose. Sedimentation and microscopic observation revealed that flocculation was induced in MA-R4 when it fermented glucose, a glucose/xylose mixture, or mannose, whereas attempts to ferment xylose, galactose, and arabinose led to the loss of flocculation. MA-R4 fermented xylose and galactose more slowly than glucose and mannose. Therefore, the various flocculation behaviors shown by MA-R4 should be useful in the control of ethanol fermentation processes.     

Adsorptive Stripping Voltammetric Determination of 2,4-Dichlorophenol by Laponite Modified Carbon Paste Electrode

A laponite modified carbon paste electrode was prepared, characterized and applied for the 2,4-dichlorophenol (2,4-DCP) voltammetric determination. It takes advantage of the ability of laponite to adsorb phenols, as well as of its availability and very low cost. Kinetic and equilibrium data for 2,4-DCP adsorption by laponite in aqueous dispersions demonstrated that the adsorption process obeyed a pseudo first order kinetic model and was consistent with the formation of adsorbed multilayers on a surface with heterogeneous pore distribution. The composite paste electrode exhibited a heterogeneous surface with 65 % increased surface area and 27 % enhanced catalytic activity compared to the unmodified one. The adsorptive stripping voltammetric determination of 2,4-DCP at an electrode with an optimized graphite:laponite ratio of 55 : 15 w% using a 3 min accumulation time at pH 5.5 was found to be suitable for its quantification in the linear concentration range extended up to 50 μmol L⁻¹ with a sensitivity of 0.56 μA L μmol⁻¹ and a LOD of 0.2 μmol L⁻¹ (S/N=3).The 2,4-DCP electrochemical response was not affected by the presence of some structurally similar phenols, like catechol and p-nitrophenol, while resorcinol, 2-chlorophenol, and 4-chlorophenol presented interferences. The results were validated by 2,4-DCP determination in spiked tap water.     

Electrochemical investigation of the interaction of 2,4-D and double stranded DNA using pencil graphite electrodes

2,4-dichlorophenoxyacetic acid (2,4-D) is an auxinic herbicide used to control broadleaf weeds. It is also a threatening factor for not only aquatic life but also human health due to its genotoxicity and endocrine disruptive property. Herein, the interaction between 2,4-D and double stranded DNA was investigated by using single-use pencil graphite electrodes (PGE) in combination with electrochemical techniques. The detection mechanism was based on the monitoring of the changes at the guanine oxidation signal obtained before/after surface-confined interaction of 2,4-D and DNA at the surface of PGE. The electrochemical characterization of the interaction was studied by using microscopic and electrochemical techniques. The response obtained by interaction in the presence of another herbicide, glyphosate, which is widely used with 2,4-D for weed control, was compared to the one occurred in the presence of 2,4-D. Electrochemical monitoring of the interaction between the herbicide whose active molecule was 2,4-D and DNA was also investigated. The detection (LOD) and quantification limits (LOQ) for 2,4-D and the herbicide could be obtained in the linear concentration ranges of 30–70 µg/mL and 10–30 µg/mL, respectively and LOD and LOQ values were found to be 2.85 and 9.50 µg/mL for both 2,4-D and the herbicide. The sensitivity of the biosensor was calculated as 0.087 µA.mL / µg.cm² .This is the first study in literature by means of not only voltammetric detection of 2,4-D and DNA interaction but also the herbicide-DNA interaction at the surface of PGE based on the changes at the guanine signal.     

Synthesis and study of a sorbent based on silica gel modified with hyperbranched poly(dichloromethylsilylpropyl)carbosilane with molecular imprints of 2,4-dichlorophenoxyacetic acid

A new sorbent for selective sorption of 2,4-dichlorophenoxyacetic acid (2,4-D) from aqueous solutions—silica gel modified with hyperbranched poly(dichloromethylsilylpropyl)carbosilane with molecular imprints of 2,4-D (SG-MI)—has been synthesized, and its specific surface area has been estimated. Sorption of 2,4-D has been studied under static conditions. Analysis of sorption isotherms shows that SG-MI is capable molecular recognition of 2,4-D. The selectivity of the sorbent synthesized was estimated for structurally related compounds.