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991.
Nataša Pejić Slobodan Anić Vesna Kuntić Vladana Vukojević Ljiljana Kolar-Anić 《Mikrochimica acta》2003,143(4):261-267
A kinetic method is described for the microquantitative (microconcentration/microvolume) determination of rutin based on potentiometric monitoring of the concentration perturbations of the Bray-Liebhafsky (BL) oscillatory reaction being in a non-equilibrium stationary state close to a bifurcation point. The experiments are carried out in an open reactor. The response of the matrix system to perturbations by different concentrations of rutin ethanolic solutions is followed by a Pt-electrode. In the concentration range between 7.8×10–8moldm–3 and 9.1×10–6mol dm–3, we found a linear dependence of the maximal potential shift, Em, on the logarithm of the rutin concentrations. The unknown concentrations can be determined from the calibration curve up to an accuracy of ±5%. The detection limit is 3.6×10–8mol dm–3. The amount of required sample can be as small as 10µL. 相似文献
992.
Hiléia K. S. Souza V. R. da Silveira F. M. M. Borges Dulce M. A. Melo H. Scatena Jr. O. A. de Oliveira A. G. Souza 《Journal of Thermal Analysis and Calorimetry》2007,87(2):433-436
Thermal behavior of rare earth nitrate complexes
with 2-azacyclononanone (AZA) with Ln(NO3)3·3(AZA)
composition (where Ln=Gd, Er and Ho) was
analyzed in kinetic point of view. Kinetic parameters were calculated from
thermogravimetric data. All obtained results were similar. The first decomposition
step was representative to the loss of ligand and the residue was essentially
Ln2O3. Furthermore, a reaction
path was proposed for the thermal decomposition of the Ln(NO3)3·3(AZA). 相似文献
993.
Xiaodong Zhang Dexu Lin Zhengmin Liu 《Journal of Radioanalytical and Nuclear Chemistry》2005,266(1):149-151
Summary The elastic scattering cross sections of natural vanadium for protons have been measured for beam energies below 2.64 MeV in steps of 10 keV and in the angular 160° and 170°. The overall standard error (ΔσExp/σExp) in the measured cross sections is estimated to be better than ±3% at all the beam energies and angles. The results are presented in graphical and tabular forms that should be useful for those who wish to use the cross sections for material analysis. 相似文献
994.
995.
T. Vlase Gabriela Vlase A. Chiriac N. Doca 《Journal of Thermal Analysis and Calorimetry》2005,80(1):87-90
Summary In order to obtain catalysts, the thermal decomposition of the precursors is a compulsory step. However, kinetic analysis of the decomposition data obtained under non-isothermal conditions lead very seldom to the intimate reaction mechanism. There is also a lack of information because in non-isothermal kinetics, the compensation effect, is rather a rule and unfortunately a source of debate. In order to discriminate between these processes, and the influence of conversion, respectively temperature on the reaction rate, the NPK (non-parametric kinetic - Sempere and Nomen) method was used. This method is based on the singular value decomposition algorithm (SVD) applied on the matrix of reaction rate at corresponding conversion and temperature. This method allows a less speculative determination of the conversion functions and of the kinetic parameters. 相似文献
996.
This work describes a structure and kinetic stability study of some complexes with the general formula MN, where M are the alkaline earth metal atoms, Be, Mg, Ca, Sr, and Ba. A complex (A) with two points of attachment to the N5 ring is the most energetically favored for all metals considered here. Except for Be, structure (B) containing a mono‐coordinated metal atom is a transition state corresponding to the metal atom transfer around the N5 ring. Pyramidal structure (C) is kinetically unstable with the low isomerization barrier height, ranging from 0.9 to 6.7 kcal/mol. The dissociation barrier heights for the lowest energy isomers (A) are predicted to be 1.2–18.7 kcal/mol (Be to Ba), indicating that kinetic stability increases from lighter to heavier metal atoms. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004 相似文献
997.
Moein B. Sayed 《Journal of Solid State Electrochemistry》2003,7(4):223-231
Variable strength H-bonding affects the mobility and so electric conduction of protons differently. Also, variable extent
mesomerism modifies electric conduction with varying dielectric features. Both these molecular modifiers are properly cited
using azophenol derivatives as model compounds for discussion of their consequences in the varying features of electric conduction.
The electric permittivity shows low-frequency dispersion characteristic of ionic conduction over mobile charge carries; the
mobility shifts at a critical temperature T
c, being structure dependent. The frequency-dependent Z′′-Z′ layout changes with temperature from linear at low temperatures to semicircular above T
c within a frame of temperature-sensitive dipole-ionic mediated conduction. The a.c. conductivity, σac, increases with frequency and temperature and becomes frequency insensitive, like d.c. conductivity, σdc, above the T
c because of the escalating contribution from the d.c. conduction. The mesomeric structure seems to prompt a dipole-based electric
conduction of high relaxation energy over the strongly associated phenolic protons that may be thermally activated above the
T
c into a much lower relaxation energy protonic conduction of up to two orders higher conductivity. The protonic conduction
emerges at a T
c that falls with a drop in the relaxation energy following a similar order of increasing proton mobility and mesomerism in
the azophenol derivatives: azocatechol>azoquinol>azoresorcinol. On the molecular level, variable temperature infrared spectroscopy
reveals higher proton mobility and mesomerism for the azocatechol derivative that demonstrates its higher protonic conductivity
at lower T
c and relaxation energy, compared to the azoquinol and azoresorcinol derivatives. This is well verified in the light of conflicting
intramolecular H-bonding that assists the proton mobility in azocatechol whereas it associates the protons in azoresorcinol
more than in azoquinol.
Electronic Publication 相似文献
998.
Microwave-assisted extraction of zearalenone from wheat and corn 总被引:9,自引:0,他引:9
Pallaroni L von Holst C Eskilsson S Björklund E 《Analytical and bioanalytical chemistry》2002,374(1):161-166
A microwave-assisted extraction (MAE) method has been developed for determination of zearalenone in wheat and corn by LC-MS with an atmospheric pressure chemical ionization interface (APCI). Matrix effects were minimized by use of matrix-matched standard curves for quantification of the analyte. The limit of quantification (LOQ) of the method was 30 ng g(-1) in wheat and 20 ng g(-1) in corn. The rapid LC-MS method enabled analysis of the extracts without clean-up, thereby reducing analyte losses, the time required for the analytical procedure, and costs. A factorial design approach was used to examine the effect on extraction efficiency of the main extraction conditions - time, temperature, and solvent. On the basis of results from statistical assessment extraction was performed with 1:1 (v/v) methanol-acetonitrile at 80 degrees C for 5 min. When these extraction conditions were applied to a wheat sample from a recently conducted international proficiency test, 92% (103 ng g(-1)) of the assigned zearalenone concentration (112 ng g(-1)) in the test material was obtained. This result was within the uncertainty (u) range of the assigned value of the test material (u=+/-15.8 ng g(-1), alpha=0.05) thereby demonstrating the accuracy of the method was sufficient. The precision of the whole method was also confirmed to be adequate, because the observed relative standard deviation (RSD) of 12% (n=10) also fulfils the quality criteria recommended by European guidelines for in-house method validation. 相似文献
999.
痕量Au Bi和Cd的萃取浮选及原子吸收光谱法测定 总被引:1,自引:0,他引:1
浮选法分离痕量金属离子,由于灵敏度高、选择性强已得到广泛应用。本文利用浮选法使Au~(3 )、Bi~(3 )和Cd~(2 )同KBr反应生成的络合阴离子与碱性染料罗丹明B(RB)生成既疏水又疏有机溶剂的三元离子缔合物,后者经甲苯浮选分出,用二甲基甲酰胺(DMF)溶解后,可用原子吸收法测定Au、Bi和Cd的含量。本方法用于海水,锌片和矿样中上述三种元素的微量测定,可提高检测灵敏度,而且K、Na、Ca、Mg等共存离子不生干扰。具体实验方法如下: 相似文献
1000.