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911.
The Flow Injection technique is shown to provide fast, reliable and sensitive methods for the determination of calcium in various aqueous as well as serum samples; spectrophotometric or potentiometric detection can be used. At sampling rates of 100–110 samples per hour, with 30-μl sample injections, high reproducibility of measurement and low reagent consumption are achieved in both methods. In the spectrophotometric method, the analytical readout is available within 12 s after sample injection at a total reagent consumption of 0.75 ml per analysis. The potentiometric measurement of the calcium activity in serum is placed on a reliable basis by alternating measurements of serum samples and aqueous standards without incurring any non-reproducible changes in potential between aqueous and serum solutions. This permits the simultaneous determination of pH and pCa, the analytical readout being available within XXX s of sample injection. The good agreement between the results obtained with the Flow Injection method and those attained by atomic absorption and EDTA titrations as well as pCa stat-measurements show that the new methods are potentially suitable for routine analysis. 相似文献
912.
Tetraethylammonium perchlorate, compared to lithium perchlorate as background electrolyte for the reduction of pyridinium ion in pyridine, is effective over a wider potential range, but is more difficult to obtain in a pure state; slight amounts of impurities do not, however, affect the pyridinium wave. The pyridinium wave produced in 0.1 M Et4NClO4 may occur at a more negative potential than the main pyridinium wave in 0.1 M LiClO4, depending on the source of the pyridinium ion, but still appears to be due to a diffusion-controlled reduction, whose limiting current is linearly proportional to concentration; the prewave observed in LiCl04 background generally does not appear in Et4NClO4 background. Specific differences in the effect of Li(I), Na(I) and Et4N(I) background cation appear to be due to electrocapillary phenomena and perhaps to the extent of solvation of the ions. The constancy of current for solutions containing acetic acid with added acetate, pyridinium nitrate with added nitrate, and benzoic acid with added benzoate indicate that the pyridinium reduction is independent of anion concentration. 相似文献
913.
914.
A method is described in which the intensity of coloration of brown manganese dioxide on white Millipore filters is taken as the measure of the manganese content. A solution of manganese(II) is made strongly basic, whereupon manganese dioxide precipitates via its auto-oxidation. Optimum conditions for the precipitation are studied. Less than 0.5 μg of manganese can be determined. 相似文献
915.
E. Abel 《Monatshefte für Chemie / Chemical Monthly》1954,85(1):227-234
Zusammenfassung Don Geschwindigkeitsbeziehungen, die unter zeitlicher Verfolgung der Autoxydation von Ferroion erhalten worden sind, werden Rektionsmechanismen zugeordnet: der charakteristische Aciditätseinfluß sei durch einen Primärschritt bedingt, der in electron transfer zwischen O2 und OH-Ion besteht, unter gleichzeitiger Anlagerung von OH; eine entsprechende Struktur wird auch jenem Mechanismus zuzuordnen versucht, der zu quadratischer Abhängigkeit der Autoxydationsgeschwindigkeit von der Ferroionkonzentration führt. 相似文献
916.
A. L. Podkorytov S. R. Kudakaeva E. V. Sokolova S. A. Shtin D. N. Ashikhmin 《Russian Journal of Inorganic Chemistry》2006,51(1):46-50
The main features of the synthesis of (Pb1-x
Srx)2Nb2O7 and (Pb1-x
Bax)2Nb2O7 pyrochlore solid solutions were determined using isothermal thermogravimetry in tandem with formal-kinetic analysis. The
stability and electron-transport properties of the triple niobates were studied, which allowed us to test them as electrode-active
materials for membranes in ion-selective electrodes (ISEs). 相似文献
917.
A computational study on the intermolecular reaction of protonated oxirane with methylpropene, as a model for initiation of oxidosqualene cyclisation, shows that the SN2-like ring opening is strongly exothermic with a low barrier to reaction and establishes the geometry of the intermolecular reaction. 相似文献
918.
V. Slavinska Dz. Sile G. Rozenthal G. Maurops J. Popelis M. Katkevich V. Stonkus E. Lukevics 《Chemistry of Heterocyclic Compounds》2006,42(5):570-573
The hydrogenation of ethyl 4-R-2,4-dioxobutyrates (R = phenyl, 2-furyl) at 5% Pt/Al2O3 catalyst, modified with cinchonidine, and at palladium black was investigated. The former had low activity under the conditions
we tested. The main products during the hydrogenation of these compounds at palladium black are ethyl 4-R-2-hydroxy-4-oxobutyrates.
The yield of the phenyl derivative amounts to 68.5%, while the yield of the corresponding 2-furyl derivative amounts to 97%.
In the last case ethyl 2-hydroxy-4-oxo-4-(2-tetrahydrofuryl)butyrate was detected as impurity. The optimum conditions for
the formation of ethyl 2-hydroxy-4-phenylbutyrate (yield 88.2%) were determined.
__________
Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 655–659, May, 2006. 相似文献
919.
Megalios EG Kapsalis N Paschalidis J Papathanasiou AG Boudouvis AG 《Journal of colloid and interface science》2005,288(2):508-512
In this paper, a novel optical device for measuring the deformation of liquid free surfaces is presented. The device employs a laser beam, which can be focused on any chosen location on the free surface. The key measurement is of the intensity of the beam reflected from a location on the free surface where the deformation exhibits a local extremum. The optics of the device is so designed as to measure a maximum intensity when the distance between the focusing lens and the selected point on the free surface is equal to the focal length, thus enabling a height measurement. The device is tested in ferrofluid pools where the height of the spikes of the normal field instability is measured. The simplicity of the suggested technique enables the fabrication of a quite cheap device for measuring surface deformation of nontransparent liquids, which provides good accuracy and reproducibility. 相似文献
920.
Curve crossing in two excited states of IBr was studied by means of photodissociation with a pulse dye laser. The ratios of the formed ground state Br(2P and excited Br(2P) were measured at various wavelengths. They are compared with ratios calculated with the Landau-Zener formula, using parameters given by Child. The agreement between the measurements and the calculations is very good. 相似文献