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991.
The design and construction of a simple device for measuring ionic concentrations (or pH) with ion-selective electrodes are described. The automated system includes a special electronic circuit with an operational amplifier, a signal conditioner and a personalcomputer. A digital multimeter can be used if automation is not required. The results obtained in tests with iodide-, chloride- and nitrate-selective electrodes and glass electrodes show very good agreement with those obtained with sophisticated commercial apparatus. 相似文献
992.
The characteristics of the mixed-ligand titanium(IV)-fluoride-alizarin complex, including the optimum conditions of formation and extraction into methyl isobutyl ketone, are described. A simple and sensitive procedure for spectrophotometric determination of titanium has been developed. At pH 9.5-10.3 titanium reacts with alizarin in the presence of fluoride to form a red-violet complex that is completely extractable into methyl isobutyl ketone, and has its absorption maximum at 513 nm. The molar absorptivity at 513 nm is 7.0 x 10(4)l.mole(-1).cm(-1). Beer's law is obeyed up to 22 mug of titanium in 30 ml of solution. The method has been used for the determination of titanium in an oxide mixture and aluminium alloy samples. 相似文献
993.
A systematic study of the fluorescence of complexes of some flavone derivatives with organotin compounds in hexane and in an aqueous micellar medium on Triton X-100 is reported. Some relationships between fluorescence intensity and the structure of the fluorogenic reagent or that of the organotin compound can be deduced, and the most suitable reagent for each organotin species can be chosen on the basis of sensitivity and selectivity. Results point out that flavone derivatives are appropriate post-column derivatization reagents for organotin compounds in liquid chromatography. 相似文献
994.
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
995.
AurelioG. Cskÿ Rocío Medel M.Carmen Murcia Joaquín Plumet 《Helvetica chimica acta》2005,88(6):1387-1396
A new method for the synthesis of spiro‐β‐lactams tethered to tetrahydrofuran rings is described. The procedure is based on Ru‐catalyzed metathesis sequences with oxanorbornene precursors easily obtained by the Staudinger [2+2] cycloaddition of related imines. 相似文献
996.
Determination of sulfametoxazole, sulfadiazine and associated compounds in pharmaceutical preparations by capillary zone electrophoresis 总被引:3,自引:0,他引:3
Berzas Nevado JJ Castañeda Peñalvo G Guzmán Bernardo FJ 《Journal of chromatography. A》2001,918(1):205-210
A capillary zone electrophoresis method is presented to separate sulfadiazine, sulfamethoxazole, trimethoprim, bromhexine and guaiacol by using a fused-silica capillary (60.2 cm x 75 microm I.D.). The separation was carried out at 30 kV and 25 degrees C in a 15 mM phosphate buffer adjusted to pH 6.2 as electrolyte. Under these conditions, the run time was 6 min and the limits of quantification were about 1 mg/l for every component. The method was applied to pharmaceutical preparations and the results provided recoveries close to 100%. 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.
Núñez Lisardo Villaneuva M. Rial B Núñez M. R. Fraga L. 《Journal of Thermal Analysis and Calorimetry》2002,70(1):75-84
The thermal degradation of the epoxy system diglycidyl ether of bisphenol A (BADGE n=0)/1,2-diamine cyclohexane (DCH) containing different concentrations of an epoxy reactive diluent was studied by thermogravimetric
analysis in order to determine the reaction mechanism of the degradation process and to compare it with the results for the
same system without diluent. The value of the activation energy, necessary for this study, was calculated using various integral
and differential methods. Values obtained using the different methods were compared to the value obtained by the Flynn-Wall-Ozawa"s
method (between 193-240 kJ mol-1 depending on the diluent concentration) with does not require a knowledge of the nth order reaction mechanism. All the experimental
results were compared to master curves in the range of Doyle"s approximation (20-35% of conversion). Analysis of the results
suggests that the reaction mechanism could be F2, F3, or A2 type.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
1000.
Immobilization of protein on ferromagnetic Dacron 总被引:1,自引:0,他引:1
A. M. A. Carneiro LeÃo E. A. Oliveira L. B. Carvalho 《Applied biochemistry and biotechnology》1991,31(1):53-58
Ferromagnetic Dacron (polyethyleneterephthalate) is proposed as a matrix to immobilize proteins covalently. Dacron in powder was magnetized by reacting ferrous (Fe+2) and ferric (Fe+3) ions with its hydrazide form at pH 8.3. Ferromagnetic hydrazide Dacron was converted to ferromagnetic azide Dacron and amyloglucosidase (E.C. 3.2.1.3) was covalently bound through the latter group. The catalytic property of the enzyme was preserved (8% of the specific activity estimated for the soluble enzyme) and all the magnetic amyloglucosidase Dacron derivative was recovered by using a magnetic field. No activity was detected in the supernatant. 相似文献