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11.
Anna Kowalska Zygmunt Kowalski Andrzej Kotarba Andrzej Barański 《Mikrochimica acta》1990,100(5-6):349-353
The analytical procedure of determination of Fe(II) in the presence of Fe(III) in milligram samples is proposed. A solid sample is dissolved in hydrochloric acid in argon atmosphere. Subsequently, the pH-value of the solution is fixed and Fe(III) complexed by phosphoric buffer. At the next step Fe(II) is oxidized by -molybdosilicic acid. Finally, the intensity of colouring caused by the reduced form of the acid is measured at the wavelength 770 nm. The proper treatment of the sample during oxidation, and immediately before, is decisive for the accuracy of the analysis. The method was verified by means of the analysis of synthetic magnetite. The theoretical content of Fe(II) was 24.12%, the determined one was 24.02 ± 0.10%. The method was applied to the determination of the homogeneity of an iron catalyst for ammonia synthesis. 相似文献
12.
Isothermal adsorption of Ar on single walled carbon nanotubes (SWNTs) has been studied at 77 and 87 K. The SWNTs have been grown by laser vaporization of a graphite pellet containing 0.6% (atomic) Ni/Co catalyst. The nanotubes have been prepared for argon adsorption measurements by prolonged outgassing of as-grown material in a vacuum at room temperature (295 K), at elevated temperatures of up to 475 K, and by oxidization for 2 h in dry air at 470 K. Formation of two condensed phases of Ar in the interior of SWNTs has been observed at 77 K. The low-density phase is formed at 155(5) microTorr, while the high-density phase, at 120(5) microTorr. At 87 K, only a single phase has been observed at 185(5) microTorr. Condensation at both 77 and 87 K appears to be the first-order phase transition. Onset of the quasi-one-dimensional linear (one-channel) phase and the quasi-two-dimensional monolayer (six-channel) phase formation on the external surface of bundles has been observed at 77 K near 0.0017 and 0.8 Torr, respectively, and at 87 K near 0.018 and 5 Torr, respectively. Isosteric heats of adsorption for the one-channel phase, the first external layer, and the second external layer have been determined to be equal to 137, 107, and 70 meV, respectively. 相似文献
13.
Summary A new sensitive, spectrophotometric determination of gallium, based on the ternary gallium-Eriochrome Cyanine R-cetyltrimethylammonium system has been developed. At
max=588 nm the molar absorptivity is 1.20×105l·mole–1·cm–1. The maximum absorbance is attained in 5 min in the presence of a 10-fold molar ratio of Eriochrome Cyanine R and an approx. 50-fold ratio of cetyltrimethylammonium bromide (to Ga). Citrate, EDTA and to a lesser extent tartrate, interfere. Interference by metals can be eliminated by a preliminary extraction of gallium with di-isopropyl ether from 7 M hydrochloric acid in the presence of ascorbic acid as reductant. The results for gallium (at a concentration level of 1×10–4%) in aluminium metal and chloride indicate good precision and accuracy.
Empfindliche spektrophotometrische Bestimmung von Gallium mit Eriochromcyanin-R- und Cetyltrimethylammonium-Ionen
Zusammenfassung Ein neues, empfindliches spektrophotometrisches Verfahren zur Galliumbestimmung wurde ausgearbeitet. Es beruht auf der Verwendung des ternären Systems Gallium — EriochromcyaninR — Cetyltrimethylammonium. Bei max=588 nm beträgt die molare Extinktion 1,20·105 1·Mol–1·cm–1. Die maximale Absorption wird innerhalb von 5 min bei Gegenwart der 10fachen molaren Menge EriochromcyaninR und der etwa 50fachen Menge Cetyltrimethylammoniumbromid erreicht. Citrat, ÄDTA und in geringerem Maß Tartrat stören. Störende Wirkung durch Metalle kann durch vorhergehende Extraktion des Galliums mit Diisopropyläther aus 7 M Salzsäure in Gegenwart von Askorbinsäure als Reduktionsmittel vermieden werden. Die Ergebnisse (im Konzentrationsbereich von 10–4% Ga) in metallischem Aluminium und AICI3 sind genau.相似文献
14.
Juliana Vaz Bevilaqua Lidia M. Lima Aline Gomes Cunha Eliezer J. Barreiro Tito L. M. Alves Lucia Moreira Campos Paiva Denise M.Guimarães Freire 《Applied biochemistry and biotechnology》2005,121(1-3):117-128
The last step of the production of four phthalimide-derived acids, designed to act as antiasthma drugs, was performed by enzymatic hydrolysis of the respective methyl or ethyl esters. The esters 4-ethyl-[2-(1,3-dioxo-1,3-dihydro-2-isoindoylyl)]-phenoxyacetic methyl ester (PHT-MET), 4-ethyl-[2-(1,3-dioxo-1,3-dihydro-2-isoindoylyl)]-phenoxyacetic ethyl ester, 4-(1,3-dioxo-1,3-dihydro-2-isoindoylyl)-phenoxyacetic ethyl ester, and 2-(1,3-dioxo-1, 3-dihydro-2-isoindoylyl)-phenoxyacetic ethyl ester were hydrolyzed by immobilized lipase. The enzymatic reaction could be used only to produce the desired 4-substituted compounds. The best result that was found to hydrolysis of PHT-MET, and, therefore, that ester was selected for optimization experiments in a three-phase system. Reactions were performed with solid biocatalyst (Lipozyme® RM IM), organic solvent phase (ethyl acetate), and aqueous phase (saturated Na2CO3 solution). To optimize the reaction conditions, an experimental design optimization procedure was used. The variables studied were the amount of enzyme, the temperature, and the volume of the aqueous solution. Time course experiments were then performed for different initial enzyme concentrations (0.5, 0.9, and 1.4 UH/mL of solvent). The optimized reaction conditions found were 20 mg of Lipozyme (0.9 UH/mLsolvent) and 5.0 mL of Na2CO3(sat) at 40°C for 6 h. 相似文献
15.
The synthesis of 8-aza-2′-deoxyadenosine ( = 7-amino-3H-1,2,3 triazolo[4,5-d]pyrimidine N3-(2′-deoxy-β-D-ribofuranoside); 1 ) as well as the N2- and N1-(2′-deoxy-β-D-ribofuranosides) 2 and 3 is described. Glycosylation of the anion of 7-amino-3H-1,2,3-triazolo[4,5-d]pyrimidine ( 6 ) in DMF yielded three regioisomeric protected 2′-deoxy-β-D-ribofuranosides, i.e. the N3-, N2-, and N4-glycosylated isomers 7 (14%), 9 (11%), and 11 (3%), respectively, together with nearly equal amounts of their α-D-anomers 8 (13%), 10 (12%), and 12 (4%; Scheme 1). The reaction became Stereoselective for the β-D-nucleosides if the anion of 7-methoxy-3H-1,2,3-triazolo[4,5-d]pyrimidine ( 13 ) was glycosylated in MeCN: only the N3-, N2, and N1-(2′-deoxy-β-D-nucleosides) 14 (29%), 15 (32%), and 16 (23%), respectively, were formed (Scheme 2). NH3 Treatment of the methoxynucleosides 14–16 afforded the aminonucleosides 1–3 . The anomeric configuration as well as the position of glycosylation were determined by combination of 13 C-NMR , 1 H-NMR , and 1D-NOE difference spectroscopy. Compound 1 proved to be a substrate for adenosine deaminase, whereas the regioisomers 2 and 3 were not deaminated. 相似文献
16.
Marcin Marczak Lidia Wolska Wojciech Chrzanowski Jacek Namieśnik 《Mikrochimica acta》2006,155(3-4):331-348
Volatile organic compounds (VOCs), due to their toxicity and persistence in the environment, are particularly important pollutants.
Some of these compounds are mutagens, teratogens or carcinogens, while others are responsible for the degradation of organoleptic
parameters such as taste and odour of water. This review focuses on a number of key procedural steps in the analysis of volatile
organic compounds (VOCs) in water samples. A wide spectrum of techniques for the isolation and preconcentration of the aforementioned
pollutants for trace organic analysis by gas chromatography are presented and discussed. The advantages and disadvantages
of these techniques are discussed and novel developments are also taken into consideration. 相似文献
17.
18.
Pulsed lasers are used mainly in lidar systems as sources of short and highly energetic light pulses. In data transmission
systems continuous wave lasers are typically applied, however it is also possible to use pulsed lasers in such systems. Such
approach seems to be especially reasonable for devices where a pulsed laser is applied anyway and executes another function
(rangefinding). The article discusses a data transmission concept based on a pulsed laser technology. Advantages and limits
of such a transmission method are described. Influence of individual transmission elements on the effective data transmission
speed is analysed. 相似文献
19.
20.
Andrew Wisel Irene Studentsova Abdurakhim Muslinkin Ramil Garaev Valeriy Danilov Lidia Schukina 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1)
Abstract The synthesis of dimephosphone (1) was carried out on Pudovik's reaction. 相似文献