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61.
The kinetics of oxidation of pectin polysaccharide as a natural polymer by permanganate ion in aqueous perchloric acid at a constant ionic strength of 2.0 mol dm−3 has been investigated spectrophotometrically. The reaction time curves showed two distinct stages, the initial stage was relatively slow, followed by an increase in the rate of oxidation at longer times. The results of the initial rates reveal first-order kinetics in permanganate ion and fractional-order with respect to pectin concentration. Kinetic evidence for the formation of an intermediate complex between the polysaccharide and the oxidant is presented. The results obtained at various hydrogen ion concentrations showed that the reaction is acid catalyzed. The added salts lead to the prediction that Mn4+ and/or Mn3+ play an important role in the autoaccleration period kinetics. A tentative reaction mechanism consistent with the kinetic results is discussed. 相似文献
62.
The thermal decomposition of some Ni(II)-carboxylate-imidazole complexes in a nitrogen atmosphere was studied non-isothermally.
From the non-isothermal thermoanalytical data, it was found that these complexes decompose through a stepwise release of imidazole
molecules and/or CO ones forming unstable intermediates which produce metal oxide or the metal as a final decomposition product.
TG in conjunction with DTG were used to evaluate the kinetic and thermodynamic parameters of the decomposition reaction. The
kinetic studies were performed employing a computer-oriented kinetic analysis of each set of W-T data obtained under constant heating rate. The diffusion processes are the decisive mechanisms for the decomposition. The
values of ΔE, A, ΔH, ΔS and ΔG for activation were calculated for the complexes and correlated to variation in their structure.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
63.
Simple and sensitive spectrophotometric methods for the assay of terfenadine are described. The first is based on the reaction of terfenadine with iodine to give a molecular charge-transfer complex, the terfenadine acting as an n-electron donor and iodine as a sigma-electron acceptor. The second depends on the formation of a highly coloured stable radical anion between terfenadine and 7,7,8,8-tetracyanoquinodimethane (TCNQ) as a pi-electron acceptor. Beer's law is obeyed over the terfenadine concentration range 0.2-1.2 mg/100 ml. The proposed methods have been successfully applied to the analysis of commercial terfenadine tablets. 相似文献
64.
A rapid, sensitive and selective LC-atmospheric pressure-chemical ionization-MS-MS method for the determination of the new antimicrobial agent, linezolid, in human plasma using selected reaction monitoring (SRM) was developed. Linezolid and the internal standard were extracted from the biological samples by solid phase extraction (SPE) and analyzed on a reversed-phase Shim Pack CLC-CN, C18 column with the mobile phase of acetonitrile and 20 mM ammonium acetate solution (4 + 1 v/v). Detection was accomplished using an LCQ mass spectrometer (Finnigan), which was programmed in positive MS-MS mode to permit measurement of the fragment ions of linezolid and internal standard at m/z 296.2 and 223.2, respectively. The assay run-time was less than 3.5 min. Quantitative analysis was based on peak area ratio of linezolid to the internal standard. Calibration plots were established over the concentration range of 0.1-20 micrograms ml-1 of linezolid with the lowest detection limit of 0.05 microgram ml-1 using 10 microliters sample volume. The SPE technique quantitatively recovered linezolid and the internal standard from the plasma samples at a percentage range of 89.1-93.7%. Determination of control samples of linezolid in plasma validated the LC-MS-MS-SRM method. Intra-assay and inter-assay precision were in the range of 5.1-11.4% relative standard deviation, whereas the intra- and inter-accuracy were in the range of 97.5-114.0% of the nominal concentrations of linezolid added. The data confirmed that the plasma samples of linezolid were stable at room temperature and when stored at -20 degrees C for at least 10 d. The developed LC-MS-MS-SRM method is recommended for the determination of linezolid in human plasma. 相似文献
65.
Maany M. Hamada Abdel-Hamid M. Shallaby Ola El-Shafai Ahmed A. El-Asmy 《Transition Metal Chemistry》2006,31(4):522-529
The complexes of thiosemicarbazide (HTS) have been prepared and characterized by spectral, thermal and magnetic studies. The
deprotonation constant of HTS and the formation constants of its complexes were evaluated pH-metrically. The Cu(II) acetate-HTS
system gave high stability. The catalytic activity of Co(II), Ni(II) and Cu(II) complexes was tested to decompose H2O2. The Co(II) complex has no activity whereas the Cu(II) complex was found to be more active than Ni(II). The different Cu(II)
complexes were tested; [Cu2(TS)(OH)2(OAc)] was highly active. All parameters affecting the reaction rate (concentration of H2O2, weight of catalyst, temperature and pH) were studied and the optimum conditions were evaluated. Attempts to increase the
activity of [Cu2(TS)(HO)2(OAc)] by mixing with superconducting cuprate sample, Nd0.1Y0.9Ba2Cu3O7-δ, will be the subject of further studies. 相似文献
66.
L. Lacikova M. E. Abdel-Hamid L. Novotny I. Masterova D. Grancai 《Chromatographia》2006,63(3-4):117-122
Plant extracts of Staphylea L. exhibit a number of biological activities which are presumably attributed to ursolic acid. A rapid and specific tandem
mass spectrometric (MS-MS) assay for the quantification of ursolic acid in the leaves of four species of Staphylea L. (Bladdernut) and in the leaves of S. pinnata L. during ontogenesis, was developed and validated. The samples were analyzed by flow injection analysis without chromatographic
separation using a transport liquid of methanol/water/formic acid (80:20:0.1 v/v/v) at a flow-rate of 0.2 mL min−1. The run cycle time was ~2-3 min injection-to-injection. Quantification was achieved using multiple reaction monitoring at
MRM transition m/z 439 > 203. Calibration curves were linear over the concentration range of 2–20 μg mL−1 with a lower limit of quantification of 2 μg mL−1 (1.8 ± 0.297, RSD: 0.165). Validation data showed that the RSD% values were in the range of 1.8 to 6.8%, whereas the % DEVs
ranged from −18 to −2% indicating reasonable and acceptable precision and accuracy, respectively. A recovery percent of 106.8
± 10.3 of ursolic acid from spiked extracts samples, indicated the specificity and reliability of tandem mass procedure for
determination of ursolic acid in the plant extracts. The derived data of sample analysis showed different contents of ursolic
acid among various Staphylea species. The highest content of ursolic acid was found in the leaves extract of S. pinnata L. Additionally, the highest amount of ursolic acid accumulated in the leaves of S. pinnata L. was in the August /September period of the year. Smaller amounts of ursolic acid were found in samples collected before
and after that time. The results obtained serve as a justification of determining the most appropriate time for collecting
plant material as a source of ursolic acid. 相似文献
67.
H. F. Aly M. M. Abdel-Hamid A. A. Abdel Rassoul 《Journal of Radioanalytical and Nuclear Chemistry》1977,40(1-2):65-73
The distribution coefficient of sulphide, sulphite, sulphate and thiosulphate anions between different concentrations of aqueous
alkali metal chloride solutions and the anion exchanger Dowex 1X8 is studied. The obtained distribution deportment of these
anions is explained in the light of water-water, anion-cation and ion-ion interactions as well as the different tendencies
of the alkali ions to hydration. Based on the separation factors encountered between adjacent anions, a chromatographic method
is adopted for isolation of the sulphur anions by gradient elution. This method is further compared with the chromatographic
procedures so far reported for separation of the investigated anions. 相似文献
68.
采用表面印迹法, 以乙烯基三甲氧基硅烷修饰的硅胶为载体, 丙烯酰胺为功能单体, N,N-亚甲基双丙烯酰胺为交联剂, 并将改性聚乙烯醇(PVA)作为辅助识别聚合物链(ARPCs)引入聚合体系中, 制备了牛血红蛋白分子印迹聚合物(MIP). 实验使用红外光谱分析了改性PVA的结构特征, 用扫描电镜(SEM)观察MIP的表面形貌, 考察了ARPCs的含量对MIP吸附性能的影响. 吸附动力学实验研究表明, 聚合体系中ARPCs的引入使MIP对模板牛血红蛋白(BHb)的吸附量明显提高|十二烷基磺酸钠-聚丙烯酰胺凝胶电泳(SDS-PAGE)结果显示, MIP对BHb的特异性吸附能力明显提高. 相似文献
69.
The transfer phenomena of quinine drug at the aqueous 1,2- dichloroethane (DCE)interface have been studied by the current- scanning polarography. The relationships be-tween the wave height and pH of aqueous phase, concentration of quinine as well as therate of water drop are discussed. The effect of supporting electrolyte, buffer solution andthe nature of organic solvent on the polarographic wave is studied. The transfer char-acteristics of quinine in aqueous phase and in organic phase are compared, The mono- pro-tonated and diprotonated quinines can both transfer at the interface so as to produce twopolarographic waves. The transfer process of quinine at the interface is simultaneouslycontrolled by diffusion and reestablishment of the disturbed protonated equilibrium ofquinine. A further investigation is made by chronopotentiometry. On the basis of thetheoretical analysis, the formulae of the limiting current are derived and discussed. Thetheoretical results are in agreement with the experimental ones. 相似文献
70.
Summary Stability constants and composition of cadmium-glycinate binary complexes were determined using cyclic voltammetry. Furthermore, binary and ternary complex equilibria for chloroacetates and glycinate with cadmium in 0.1M aqueous KNO3 atpH 10.4 and 298 K were investigated. Cadmium forms binary complexes with chloroacetates of low stability and ternary ones with chloroacetate-glycinate of significant stability.
Gleichgewichte in wäßrigen Cadmium-Chloroacetat-Glycinat-Systemen. Untersuchungen mittels zyklischer Voltammetrie
Zusammenfassung Gleichgewichtskonstanten und Zusammensetzung binärer Cadmium-Glycinat-Komplexe wurden mittels zyklischer Voltammetrie bestimmt. Weiters wurden binäre und ternäre Gleichgewichte von Chloroacetaten und Glycinat mit Cadmium in 0.1M KNO3 beipH 10.4 und 298 K untersucht. Cadmium bildet binäre Komplexe geringer Stabilität mit Chloroacetaten und ternäre Komplexe von beträchtlicher Stabilität mit Chloroacetaten und Glycinat.相似文献