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901.
Procedures are proposed for the determination of phosphorus and silicon in the ppM range, by extraction of phosphomolybdic and silicomolybdic acids with organic solvent, decomposition of the complex and spectrophotometric determination of its molybdenum content. 相似文献
902.
Summary There were studied the process of styrene polymerization in PVC swollen surface layer initiated by free radicals generated under the action of chemical potential gradient as an external force. It was found that conversion of styrene into the block copolymer is an diffusion controlled process.
Dedicated to ProfessorV. Kellö in celebration of his 60th birthday. 相似文献
Zusammenfassung Die Initiation des Prozesses der Polymerization von Styrol in den Oberflächenquellungsschichten von PVC wurde untersucht.Dabei wurde festgestellt, daß die freien Radikale, welche bei Zerreißung von spannungsbeanspruchten Bindungen, wie sie durch Einfluß von äußeren Kräften auf den Gradienten des chemischen Potentials des Quellungsmittels an Oberflächenquell bildungsmittel Polymer entstehen können, Polymerizationsprozesse des olefinischen Quellungsmittels initiieren können.
Dedicated to ProfessorV. Kellö in celebration of his 60th birthday. 相似文献
903.
The electronic spectra of tetrathiotetracene (TTT) and of its mono- and dipositive ions have been calculated by the Pariser-Parr-Pople (PPP) method. Furthermore, the band polarizations of the first two bands of TTT have been measured. A reasonable band assignment is given using a new set of PPP parameters based on spectral data of a naphthalene derivative containing similar typical weak S-S bond. Other physical parameters as ionization potential, disproportionation energy, S-S bond length and net π-charges are discussed. 相似文献
904.
An isotope analytical method for the simultaneous determination of35S and14C in double-labelled organic compounds by liquid scintillation counting is described. The sample is burned in a stream of
oxygen. Sulfur oxides are converted to sulfuric acid and separated from other combustion products, including carbon-14 dioxide,
on a heated quartz wool column previously wetted with hydrogen peroxide. Carbon dioxide is collected from the gas stream by
an absorbent suitable for liquid scintillation counting. The residual sulfuric acid is rinsed off the column with water and
the aqueous solution obtained is mixed with a liquid scintillation cocktail for radioactivity measurement. The final solutions
ready for counting are obtained in less than fifteen minutes, quantitative collection recovery is achieved and no cross contamination
occurs. 相似文献
905.
L. A. Sáenz-Carbonell I. E. Maldonado-Mendoza O. Moreno-Valenzula R. Clau-Uitz M. López-Meyer C. Oropeza V. M. Loyola-Vargas 《Applied biochemistry and biotechnology》1993,38(3):257-267
The release of alkaloids from root culturesDatura stramonium andCatharanthus roseus and thiophenes from root cultures ofTagetes patula was found to increase when the pH of the culture media (ranging from 4.8 to 7.0) was reduced to 3.5. The extent of the effect
was different in each type of culture. Increases ranged from 4- to 20-fold, which in some cases accounted for 75% of the total
secondary metabolite pool produced per flask. When the release of individual metabolites was measured, even larger increases,
were observed (nearly 400-fold for ajmalicine). Increased release of alkaloids fromC. roseus roots were also observed in cultures growing in a 14-L fermentor, when the medium pH was reduced. Reduction of the pH of
the media did not affect growth of the root cultures in subsequent subcultures. The importance of this treatment as a stategy
to improve the recovery of secondary metabolites from producing cultures is discussed. 相似文献
906.
Tomás Pérez-Ruiz Carmen Martínez-Lozano Virginia Tomás Antonio Sanz Jesús Martín 《Fresenius' Journal of Analytical Chemistry》1998,362(4):399-403
A flow-injection configuration is proposed for the fluorimetric determination of ethylenethiourea. The procedure is based
on the inhibitory effect of ethylenethiourea on the oxidation of thiamine to thiochrome by mercury(II). A linear calibration
graph was obtained between 0.1 and 2.0 μg mL–1, with a sampling rate of 40 samples per hour and a relative standard deviation of about 1.11%. The usefulness of the method
was tested for the determination of ethylenethiourea residues in water, milk, potatoes, pear, grape and apple.
Received: 26 January 1998 / Revised: 6 April 1998 / Accepted: 9 April 1998 相似文献
907.
M. Pyldme é. Buzágh-Gere J. Pyldme M. Veiderma 《Journal of Thermal Analysis and Calorimetry》1976,10(2):195-204
The thermal reactions between Maardu (Estonia) phosphorite and acidic phosphates were investigated. TG, DTG and DTA of mixtures with H3PO4, Ca(H2PO4)2 · H2O, Ca2P2O7 and [Ca(PO3)2]n in different molar ratios showed a maximum mass loss when the CaO P2O5 value was 2. The main temperature ranges of the mass losses were determined. The probable reactions relating to the mass losses are given on the basis of the thermal curves and IR spectra.
Zusammenfassung Die thermische Reaktion zwischen Phosphorit aus Maardu (Estnien) und sauren Phosphaten wurde untersucht. TG, DTG und DTA von Gemischen mit H3PO4, Ca(H2PO4)2 · H2O, Ca2P2O7 und [Ca(PO3)2]n in verschiedenen molaren VerhÄltnissen zeigten den grö\ten Massenverlust bei dem VerhÄltnis von CaO P2O5=2. Die wichtigsten Temperaturbereiche der Massenverluste wurden bestimmt. Die den Massenverlusten zugeordneten wahrscheinlichen Reaktionen werden aus den erhaltenen thermischen Kurven und IR Spektren ermittelt.
Résumé Etude de l'effet thermique lié à la réaction entre la phosphorite de Maardu (Estonie) et les hydrogénophosphates. Etude par TG, TGD et ATD de mélanges de H3PO4 avec Ca(H2PO4)2 · 2 H2O, Ca2P2O7 et [Ca(PO3)2]n réalisés avec différents rapports molaires; mise en évidence d'une perte de masse maximale pour le rapport CaO P2O5 égal à deux. Détermination des principaux domaines de température où s'effectuent les pertes de masse. On donne les réactions probables correspondant aux pertes de masse en s'appuyant sur les courbes d'analyse thermique et spectres infrarouges.
() . TG, DTG DTA H3PO4, Cc(H2PO4)2. H2O, Ca2P2O7 [Ca(PO3)2] n , CaOP2O5 2. . , .相似文献
908.
The structure and properties of non-pyrophoric skeleton catalysts prepared from NiSi, NiAlSi, NiMg and NiZn alloys have been studied—apart from other thermal methods—by means of the derivatograph.Our experimental results have contributed to the explanation of the non-pyrophoric behaviour of these catalysts. We demonstrated that the desorption of the hydrogen content in our catalysts is not accompanied by the oxidation of active nickel. This oxidation takes place only at higher temperatures, above 200°C, at a rate proportional to the amount of active nickel.Other constituents of the catalysts (adsorbed water, hydroxide content) were also determined from the experimental data. The outstandingly high Mg(OH)2 content of the NiMg catalyst indicates that its structure is dissimilar: Mg(OH)2 also acts as support for the catalyst. 相似文献
909.
Summary A procedure has been developed for the activity measurement of tritium-labelled organic compounds in the gas phase. The organic compounds are pyrolysed in hydrogen carrier gas at 1150° and the decomposition products are swept through a carbon packing in accordance with the principle of the oxygen determination developed byUnterzaucher andBürger. The radioactive gas mixture obtained from the sample is swept by the hydrogen carrier gas flowing continuously through the reactor into a proportional counter tube, after the addition of propanebutane counter gas. By closure of the counter tube at a suitable moment, the radioactive gas is quantitatively trapped in the counter tube. The activity is measured in the limited proportional region. No memory effect occurs. The preparation of the sample requires 12 minutes; the relative standard deviation of analysis is <0.5%.
Zusammenfassung Ein Verfahren zur Aktivitätsbestimmung bei tritium-markierten organischen Verbindungen in der Gasphase wurde ausgearbeitet. Die organischen Substanzen werden in Wasserstoff als Trägergas bei 1150° pyrolysiert. Die Zersetzungsprodukte werden wie bei der Sauerstoffbestimmung nachUnterzaucher bzw.Bürger über eine Kohleschicht geleitet. Das radioaktive Gas-gemisch aus der Probe gelangt mit dem kontinuierlich strömenden Trägergas in ein Proportionalzählrohr, nachdem Propan-Butan-Zählgas zugesetzt wurde. Man schließt das Zählrohr im richtigen Augenblick, um das radioaktive Gas quantitativ zu erfassen. Die Aktivität wird im Proportionalbereich gemessen. Ein Memory-Effekt tritt nicht auf. Die Vorbereitung der Probe beansprucht 12 Minuten. Die relative Standardabweichung ist kleiner als 0,5%.相似文献
910.
Capillary electrochromatography (CEC) has been utilized to analyze free fatty acids (FFAs) and fatty acid phenacyl esters (FAPEs) originating from vegetable oils and margarine. The analyses were performed on capillaries 25 and 40 cm long, 100 microm ID, and packed with 3 microm Hypersil ODS. Isocratic elution was achieved with the mobile phase acetonitrile/50 mM 2-(N-morpholino)ethane sulfonic acid (MES), pH 6, at a ratio of 9:1. For quantitative analysis, the formation of FAPE derivatives is preferred. Moreover, the number of double bonds in the FAPEs can be elucidated by measuring the UV absorbance ratio of 240:210 nm. For the determination of the oleate/elaidate ratio in margarines, the FFAs are analyzed because of overlap of elaidate/palmitate in FAPE analysis. Data obtained with CEC and micro liquid chromatography (LC) were compared and CEC was found to be far superior in terms of efficiency and speed of analysis. Important selectivity differences were noted between micro LC on highly endcapped ODS and CEC on the silanol-rich Hypersil ODS. 相似文献