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利用电化学方法和ESR(电子自旋共振)-电化学联用技术在无水乙醇体系中研究了藏红T(ST)的电化学还原行为。通过就地跟踪其1-电子还原的中间产物——自由基,推测了该自由基的结构。观察到ST电化学还原过程中存在着后续的、平行的零级和一级衰变反应。这一事实使有的电极反应与酶催化反应相关联的论点进一步得到实验的印证和支持。根据对不同浓度的ST溶液在不同还原电位下生成自由基行为研究结果,提出了ST在该溶液体系中的还原机理,并用曲线拟合法推算了反应历程中有关步骤的动力学参数。 相似文献
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利用现场红外光谱电化学法、红外光谱循环伏吸法(CVA)和导数循环伏吸法(DCVA)研究了对硝基苯酚(PNP)在乙腈中的氧化还原机理,并结合B3LYP方法在6-311++G*水平上计算得出反应中自由基阴离子和二聚体可能的结构.通过循环伏安曲线(CV)和快速扫描红外光谱验证了在电化学还原过程中PNP在乙腈溶剂中发生较复杂的自质子化反应,并且PNP的电化学行为受其浓度的影响.当PNP浓度较高时,PNP在还原成自由基阴离子后发生自质子化作用,然后自由基阴离子与质子化产物得到电子发生二聚反应,随后PNP阴离子还原成二价阴离子;当PNP浓度较低时,电化学还原机理会发生改变,二聚现象消失,阴离子自由基继续还原. 相似文献
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铁-三乙醇胺媒质中靛蓝的间接电化学还原 总被引:1,自引:0,他引:1
铁-三乙醇胺(Fe-TEA)可作为媒质用于间接电化学法还原靛蓝.本工作采用循环伏安法研究了靛蓝在Fe-TEA媒质中的电化学行为,比较了石墨、银、镍、不锈钢四种阴极材料的电催化性能,探讨了靛蓝间接电还原的机理.此外,还进行了一组L9(34)正交电解实验,通过正交实验分析了各因素对电流效率的影响.实验结果表明:在Fe(III)-TEA媒质中,以不锈钢网为阴极可实现靛蓝的间接电化学还原,最高电流效率可达44.7%.在实验所设计因素水平范围内,对电流效率影响最大的因素为Fe(III)-TEA媒质浓度.在靛蓝的间接电还原过程中存在一种靛蓝自由基,该自由基能起到靛蓝电还原的媒质作用,在一定实验条件下,该靛蓝自由基的媒质作用可以大于Fe(III)-TEA. 相似文献
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运用循环伏安法(CV)和原位紫外-可见光谱电化学法研究了二苯胺(DPA)和邻氨基酚(OAP)在4mol/L H2SO4中单独聚合及二者共聚的电化学过程。DPA和OAP单独聚合及二者共聚时不同的电化学行为表明DPA和OAP之间发生了共聚作用。原位紫外-可见光谱研究表明,在DPA与OAP的共聚过程中,DPA与OAP首先被氧化生成阳离子自由基,然后,两者的阳离子自由基与溶液中的DPA和OAP单体或其自由基发生交互反应产生混合二聚物中间体,其吸收峰位于508 nm处。进一步研究发现,DPA和OAP的共聚过程与溶液中各单体的浓度比有关。 相似文献
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采用循环伏安法(CV)和现场光谱电化学方法从分子水平上研究了对苯醌(BQ)在4种离子液体中铂电极上的电化学氧化还原过程.基于在298.15~343.15 K温度范围内对苯醌的伏安曲线,获得了不同温度下对苯醌的扩散系数(D),进而求得其扩散活化能(Ea).利用现场红外光谱电化学循环伏吸及导数循环伏吸法同时跟踪电化学过程中反应物、中间体及产物随时间(电位)的变化.光谱电化学结果表明,苯醌在1-丁基-3-甲基咪唑四氟硼酸盐(BMIMBF4)和1-丁基-3-甲基咪唑六氟磷酸盐(BMIMPF6)中与在乙腈中类似,先生成苯醌阴离子自由基,随后进一步还原为二价阴离子. 相似文献
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Two methods have been developed for the determination of voriconazole, a new antifungal drug, in tablets. A UV method, with detection at 255 nm, was compared with a diffusion agar bioassay, which used Sacharomyces cerevisiae ATCC 2601 as the assay organism. The developed methods were linear in the range of 3.0-12.0 and 12.0-24.0 microg/mL, for the microbiological and UV methods, respectively, both exhibiting a coefficient correlation of 0.9999. The UV method demonstrated an improved precision compared to the bioassay method (1.0 versus 2.4%). The average recovery, 99.8 and 100.9%, was suitable in both methods. The results obtained by these 2 methods were compared with those of a high-performance liquid chromatography (HPLC) method published previously, and no evidence of significant difference was observed. The proposed methods are appropriate for the determination of voriconazole in tablets and can be used in routine quality control. 相似文献
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Wolfhard Wegscheider 《Accreditation and quality assurance》1999,4(11):478-479
There is much discussion in chemical metrology about the definition of primary methods of measurement, just as a couple of
years ago there was debate about its predecessors, absolute methods and definitive methods. It is argued in this paper that
the designation of certain methods as being primary only makes sense if there is an outstanding property identified that is
common to all primary methods, and not present for all non-primary methods. The aim to identify primary methods should not
blur our notion that it is the good practice of analytical chemistry that produces good results, not a particular method of
analysis. 相似文献
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食品中铝检测方法研究进展 总被引:1,自引:0,他引:1
介绍了食品中铝的来源,并综述了近十年中食品中铝测定方法的研究进展,包括电感耦合等离子体原子发射光谱法、电感耦合等离子体质谱法、石墨炉原子吸收光谱法、电化学分析法以及分光光度法等方法(引用文献75篇)。 相似文献
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Use of Thermoanalytical Methods in Prediction of Thermal Endurance of Insulating Impregnating Varnishes 总被引:1,自引:0,他引:1
Z. Kowalewski J. Zawadzka B. Górnicka 《Journal of Thermal Analysis and Calorimetry》2000,60(1):279-286
The results of testing the thermal properties of insulating impregnated varnishes obtained by thermoanalytical methods and
based on the IEC 216 standard are presented. It was found that the temperature index determined by means of thermoanalytical
testing is quite close to that derived by a conventional standardized procedure. It was also established that thermoanalytical
methods could be used in the recipe selection for the development of a new varnish.
The results obtained confirmed the possibility of using thermoanalytical methods for a quick, prognostic estimation of the
thermal endurance of insulating impregnating varnishes.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
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There are many methods for analyzing solid-state kinetic data. They are generally grouped into two categories, model-fitting and isoconversional (model-free) methods. Historically, model-fitting methods were widely used because of their ability to directly determine the kinetic triplet (i.e., frequency factor [A], activation energy [E(a)], and model). However, these methods suffer from several problems among which is their inability to uniquely determine the reaction model. This has led to the decline of these methods in favor of isoconversional methods that evaluate kinetics without modelistic assumptions. This work proposes an approach that combines the power of isoconversional methods with model-fitting methods. It is based on using isoconversional methods instead of traditional statistical fitting methods to select the reaction model. Once a reaction model has been selected, the activation energy and frequency factor can be determined for that model. This approach was investigated for simulated and real experimental data for desolvation reactions of sulfameter solvates. 相似文献
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AOAC International methods committee guidelines for validation of qualitative and quantitative food microbiological official methods of analysis 总被引:1,自引:0,他引:1
Feldsine P Abeyta C Andrews WH;AOAC International Methods Committee 《Journal of AOAC International》2002,85(5):1187-1200
Responding to a need for a guide for conducting Official Method validation studies of microbiological methods, AOAC utilized the experience of three microbiologists who have been active in the field of method validation. In collaboration, a document was prepared which covered the following areas: terms and their definitions associated with the Official Methods program (e.g., reference methods, alternative methods, and ruggedness testing), protocols and validation requirements for qualitative methods versus those for quantitative methods, the concept of the precollaborative study, ruggedness testing, tests for significant differences, performance indicators, and the approval process. After its preparation, this document was reviewed by the members of the Methods Committee on Microbiology and Extraneous Materials and by members of the Official Methods Board. Herein is presented the approved version of that document. 相似文献
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Accurate and efficient prediction of melting points for complex molecules is still a challenging task for molecular simulation, although many methods have been developed. Four melting point computational methods, including one free energy-based method (the pseudo-supercritical path (PSCP) method) and three direct methods (two interface-based methods and the voids method) were applied to argon and a widely studied ionic liquid 1-n-butyl-3-methylimidazolium chloride ([BMIM][Cl]). The performance of each method was compared systematically. All the methods under study reproduce the argon experimental melting point with reasonable accuracy. For [BMIM][Cl], the melting point was computed to be 320 K using a revised PSCP procedure, which agrees with the experimental value 337-339 K very well. However, large errors were observed in the computed results using the direct methods, suggesting that these methods are inappropriate for large molecules with sluggish dynamics. The strengths and weaknesses of each method are discussed. 相似文献
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S. Yu. Kudryashov Yu. I. Arutyunov L. A. Onuchak 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2007,81(1):102-107
New methods for calculating the mean volumetric flow rate of the carrier gas and the retention time of the unretained substance in the column under conditions of gas chromatography were proposed. The methods are based on preliminary isothermal calibrations of the flow rate and holdup time for a packed column. A theoretical substantiation of the methods was given. Procedures of plotting calibration dependences for determining the indicated quantities at a desired temperature were described. The calculation results were compared to experimental data obtained by traditional methods. It was demonstrated that the use of calculation methods substantially simplifies the determination of the specific retention volume over a wide temperature range. 相似文献
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Equivalence of a high-performance liquid chromatographic assay and a bioassay of azithromycin in human serum samples. 总被引:2,自引:0,他引:2
Two sensitive methods for the determination of the azalide antibiotic azithromycin in human serum were compared. High-performance liquid chromatography (HPLC) and a microbiological assay were simultaneously applied to 768 serum samples obtained in a clinical study. There was excellent agreement between the azithromycin concentrations measured by HPLC and by the bioassay. The correlation coefficient for the two methods was r2 = 0.96. The precision and the sensitivity of the methods were found to be very similar. 相似文献
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Techniques for the direct analysis of powdered samples provide an advantageous alternative to methods using wet digestion in sample preparation. The direct spectrochemical methods based on electrothermal vaporization (ETV-ICP-OES, solid-ETV-AAS, etc.) show a great similarity to the classical method of dc arc excitation, used in spectrography. Owing to this, the classical dc arc spectrographical method was used in parallel with ETV methods in the direct solid sampling analysis of river and basin sediments. The calibration procedure is the major difficulty of all techniques applied to direct solid sample analysis because of a lack of suitable reference materials. Consequently, it was necessary to verify the application of model calibration samples, preferentially using the simple dc arc OES system and both spectrographic and spectrometric evaluation. The performance parameters of the methods mentioned are compared with those published for the ETV-ICP-OES and SS-ETV-AAS methods. 相似文献