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951.
Mark F. Zaranyika Canissius Nyakonda Peter Moses 《Fresenius' Journal of Analytical Chemistry》1991,341(10):577-585
Summary The effects of excess Na on the ionization and excitation of K in an air-acetylene flame were studied using absorbance signal and emission signal ratios, A/A and E/E respectively, as probes, where A and E are the line absorbance and line emission readings in the presence of excess Na interferent, and unprimed quantities represent readings in the absence of the interferent. An emission signal enhancement which increases exponentially as the ratio of interferent to analyte increases (up to about 2000), was observed irrespective of whether measurements were made from the primary or secondary reaction zones of the flame, while a similar line absorbance signal enhancement was observed only when measurements were made from the primary reaction zone. For both line emission and line absorbance, the maximum enhancements observed are in excess of those predicted on the basis of complete suppression of ionization of analyte atoms as a result of the increased partial pressure of electrons. A steady state kinetic model is presented, which takes into account radiative recombination collisional excitation of K+ ions and collisional charge transfer between the heavy particles, and whose predictions are consistent with the observed interference effects. 相似文献
952.
Micellar electrokinetic chromatography of proteins 总被引:1,自引:0,他引:1
Micellar electrokinetic capillary chromatography (MECC) of proteins is a high resolution capillary electrophoretic (CE) analysis method that utilizes the hydrophobic and electrostatic interaction of protein analytes with surfactant micelles present in the buffer medium to facilitate separation. Through the manipulation of the protein-micelle interaction by the adjustment of variables such as surfactant concentration, solution pH, ionic strength, the presence of an organic modifier and the use of coated capillaries, MECC analyses of a wide variety of proteins have been optimized. MECC has been demonstrated to provide resolution of mixtures consisting of proteins with minor structural variations and also has provided the successful quantitative analysis of protein present in complex matrices. The adoption of protein MECC as a routine analytical technique may be dependent upon the successful interface of MECC with detection methodology, such as mass spectrometry, which can provide analyte characterization information. 相似文献
953.
Mark T. DeMeuse 《先进技术聚合物》1995,6(2):76-82
A review of work which has been performed on high temperature polymer blends is presented. The discussion is divided into miscible and immiscible blends. It is pointed out that one problem with miscible polymer blends is that of processing in the miscible state. In the case of immiscible blends, particularly ones containing liquid crystal polymers, the issue of adhesion of the two phases is discussed. Finally, the need for better theoretical models for predicting miscibility in polymer blends is highlighted. 相似文献
954.
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
955.
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
956.
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
957.
The results obtained for silver in Canadian reference ores and concentrates and in zinc-processing products by three atomic-absorption spectrophotometric methods are compared. "Wet chemical" methods based on the decomposition of the sample with mixed acids yield more accurate results than those based on fire-assay collection techniques. A direct acid-decomposition method involving the determination of silver in a 20% v/v hydrochloric acid-1% v/v diethylenetriamine medium is recommended for the determination of approximately 10 mug g or higher levels of silver. A method based on chloroform extraction of the tribenzylamine-silver bromide ion-association complex from 0.08M potassium bromide-2M sulphuric acid is recommended for samples containing < 10 mug of silver per g. 相似文献
958.
The perfect matching vector and forcing and the Kekulé-vector of cata-benzenoids are defined. Two theorems are given which
set the sufficient and necessary conditions for HKZ-vector (Harary et al. J Math Chem 6:295, 1991) and Kekulé-vector in cata-benzenoids.
Additional two theorems are obtained which give sharp bounds for the modules of HKZ- and Kekulé vectors.
Dedicated to Professor Tadeusz Marek Krygowski on the happy occasion of his 70th birthday. 相似文献
959.
Carbon dioxide emulsion assisted loading of polymer microspheres toward sustained release materials 总被引:2,自引:0,他引:2
Baker GA Campbell ML Yates MZ McCleskey TM 《Langmuir : the ACS journal of surfaces and colloids》2005,21(9):3730-3732
An organic solvent-free method for encapsulating progesterone at high loadings within micron-sized inert latex polymer beads is reported. This approach makes use of a polymeric surfactant to emulsify carbon dioxide into an aqueous latex suspension. In this way, preformed approximately 4 microm polystyrene (PS) microparticles surface-grafted with poly(N-vinylpyrrolidone) (PVP) were plasticized and swollen followed by rapid partitioning of progesterone into the polymer matrix. The as-prepared polystyrene beads incorporated over 10% progesterone by weight while maintaining their initial size and morphological uniformity. Dissolution experiments were also carried out to obtain the release profile of progesterone entrapped within the PVP/PS particles. 相似文献
960.
Watson MD Jäckel F Severin N Rabe JP Müllen K 《Journal of the American Chemical Society》2004,126(5):1402-1407
Cyclophanes with the largest-to-date polycyclic aromatic hydrocarbon (hexa-peri-hexabenzocoronene, HBC) to be entrained in such a structural motif are reported. The two disks are covalently captured by intermolecular ring-closing olefin metathesis of dienes in good yield. DSC, optical microscopy, and WAXD show the new cyclophanes to self-assemble to thermotropic columnar liquid crystal mesophases similar to monomeric analogues. Solution spectroscopic studies reveal that the two disks within a single unit lie face-to-face, with a small average lateral offset. Self-assembly into two-dimensional crystals at a solid-liquid interface was visualized by STM, and the electrical properties of single molecules were assessed by scanning tunneling spectroscopy revealing a diode-like behavior which is similar to that previously reported for single HBC disks, laying the groundwork for future electrical interrogations of dynamic molecular complexes. 相似文献