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891.
A number of biphenylisopropyloxycarbonyl-blocked amino acids have been synthesized as their cyclohexylamine or dicyclohexylamine salts, and their properties described. A facile method for regenerating the Bpoc-amino acids from their salts is detailed, along with the conditions used to determine that the syntheses are free of racemization. 相似文献
892.
Summary The potentiometric determination of tetraphenylborate with silver nitrate solution was investigated a) at i=0 in the presence of calomel reference electrode and silver resp. silicone rubber based halide-selective indicator electrodes and b) at i0 in the presence of silver (cathode)-calomel, silver-silver, silver-platinum, platinum-silver and graphite-silver electrode couples. An indirect method is described for the determination of potassium ions with potentiometric end-point indication. Experiments were also carried out in order to develop methods for the titration of silver, potassium and thallium(I) ions with sodium tetraphenylborate solution in the presence of anodic polarized graphite and calomel reference electrodes. The relative standard deviations were 0.38–0.49% for tetraphenylborate, 1.96% for potassium and 1.07% for thallium(I).
Potentiometrische Bestimmung von Tetraphenylborationen mit Silbernitrat. Bestimmung von Silber, Kalium und Thallium(I)
Zusammenfassung Die Möglichkeit der potentiometrischen Bestimmung von Tetraphenylborat mit Silbernitrat wurde untersucht a) in Anwesenheit von Kalomel-Bezugselektrode und Silber- bzw. haloidselektiven Silicongummi-Indicatorelektroden bei i=0 und b) in Anwesenheit von Silber (Kathode)-Kalomel-, Silber-Silber, Silber-Platin-, Platin-Silber- und Graphit-Silber-Elektrodenpaaren bei i0. Eine Methode zur indirekten potentiometrischen Bestimmung von Kalium sowie Verfahren zur Bestimmung von Silber-, Kalium- und Thallium(I)-ionen mit Natriumtetraphenylboratlösung in Anwesenheit einer anodisch polarisierten Graphitelektrode und einer Kalomel-Referenzelektrode wurden ausgearbeitet. Die relativen Standardabweichungen betragen für Tetraphenylborat 0,38–0,49%, für Kalium und Thallium 1,96 bzw. 1,07%.相似文献
893.
从光干涉方式,瞳窗关系和光源带宽等基本关系出发,利用空间不变系统理论解析了相移显微干涉检测系统中衍射效应的影响。为了减小横向分辨率对纵向分辨率的影响,利用相关信息提取或数字滤波的方法,获得了纳米分辨率的三维形貌。 相似文献
894.
Li Shu-Min Miao Yan-Gang Zhou Zi-Fang Chen Ji Liu Yao-Yang 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1997,39(1):29-34
The first Born approximation is used to study the laser-assisted electron capture by a fast proton from a hydrogen atom. The laser modification on differential cross section peaks sharply in the forward direction. With the impact energy increasing, the change in integral cross section becomes notable. The more intense the laser, the greater the cross section is; the lower the frequency, the greater the cross section. 相似文献
895.
Analytical fractionation of aquatic humic substances and their metal species by means of multistage ultrafiltration 总被引:2,自引:0,他引:2
Brit Aster P. Burba Jose A. C. A. C. Broekaert 《Fresenius' Journal of Analytical Chemistry》1996,354(5-6):722-728
The molecular-size fractionation of aquatic humic substances (HS) and their metal species by means of a novel sequential-stage ultrafiltration (UF) device equipped with five appropriate ultramembranes (1, 5, 10, 50 and 100 kD) is described. First of all, the concentration dynamics of macromolecules, particulary HS, during five-stage UF and its subsequent washing step has been modelled. Based on these results, the fractionation of aquatic HS (from ground and bog water) by means of multistage UF has been optimized for an analytical scale (10 ml sample, 1 mg/ml HS, 10 ml washing solution, pH 6.0). The molecular size-distribution of selected aquatic HS (BOC 1/2 from the DFG-Versuchsfeld Bocholt, VM 5 from Venner Moor, Germany) studied by five-stage UF exhibited strong systematic influences of the procedure used for their isolation. The molecular-size distribution of HS obtained by on-line UF and gel permeation chromatography (GPC) showed a satisfactory agreement in the range 1–50 kD. Moreover, when interrupting multistage UF for > 48 h a slow transformation in the HS samples has been found as gradually additional HS fractions of < 1 kD have been formed. Besides unloaded HS molecules, the molecular-size distribution of freshly formed metal species of HS (1.0 mg metal/g HS of Al(III), Cd(II), Cu(II), Fe(III), Mn(II), Ni(II), Pb(II), Zn(II), each) has been characterized by multistage UF as a function of pH-value, degree of loading and complexation time. Metal determinations as carried out by flame AAS, showed that considerable metal fractions in HS especially are present in molecules > 50 kD, which seemed to be rather acid-inert. With complexation times of < 2 days a transient shift of the molecular size distribution of both HS and their metal species (e.g., Al(III), Fe(III) to higher values (> 10 kD) has been found. 相似文献
896.
Conclusions On the basis of UV, IR, and NMR spectroscopy, and the preparation of derivatives, the most probable structures of ursinoic acid and ursinin, aromatic oxo acids isolated previously from the roots ofAngelica ursina Rupr. et Schmalh., have been established. It has been shown that the former has the structure 2,2-dimethylpyrano-5, 6:5, 6-(2, 4-dimethoxy)benzoylacetic acid while the second is 2,2-dimethylpyrano-5,6:5, 6-(2-methoxy)benzoylacetic acid.Khimiya Prirodnykh Soedinenii, Vol. 6, No. 4, pp. 421–424, 1970 相似文献
897.
Summary Polarographic studies have been made of the reaction between Cerium(IV) and potassium thiocyanate in acidic medium. CeIVin the concentration range 2 · 10–4 M to 5 · 10–3 M was found to be reduced to CeIII by thiocyanate ion. One equivalent of thiocyanate reduced 4–6 equivalents of CeIV in the concentration range studied.
Zusammenfassung Die Reaktion zwischen CerIV und Kaliumthiocyanat wurde in saurem Medium polarographisch untersucht. CerIII wurde im Bereich von 2 · 10–4 m bis 5 · 10–3 m von Thiocyanat zu CerIII reduziert. In diesem Konzentrationsbereich entsprachen einem Äquivalent Thiocyanat 4–6 Äquivalente CerIV.相似文献
898.
A new and original method of synthesizing difficultly accessible 1-hydrosilatranes, is developed. It is based on transesterification of the appropriate boratranes in the presence of aluminum alkoxide catalyst. The method is used to prepare four compounds of the type stated, only one of which (R=R=R"=H) was previously known.For Part X see [1]. 相似文献
899.
Tunli Chen 《中国化学会会志》1969,16(4):115-122
This is an experimental study of the hydrogen-bonded butanediols. Infrared spectra of those butanediols were recorded for pure liquid and vapor phase. Although those molecules do not have any symmetry, with the aid of normal coordinate analysis of n-butane, assignments have been made for all observed infrared frequencies. 相似文献
900.
Jan Vorlíek Milan Fara Frantiek Vydra 《Fresenius' Journal of Analytical Chemistry》1968,241(5):314-318
Summary Conditions for the magnesium determination in alkaline solution by EDTA titration with biamperometric indication were examined. The most preferable pH range was found to be above 9.6. A reliable determination can be carried out in the presence of Ca, Ni, Cu and Co up to the ratio of 11. In the case of higher concentrations of Cu and Ni masking with potassium cyanide can be used. In this case, however, a change of the titration curves occurs.A new method for the determination of water-hardness by biamperometric indication is proposed. It is rapid and accurate and meets the requirements of routine and research work (error: ±1%).
Part XV: Vorlíek, J., and P. Peták: Microchem. J. 12, 466–471 (1967). 相似文献
Zusammenfassung Die Bedingungen für die Magnesiumbestimmung in alkalischer Lösung durch Titration mit ÄDTA bei biamperometrischer Endpunktsanzeige wurden untersucht. Der günstigste pH-Bereich liegt über 9,6. Zuverlässige Bestimmungen können in Gegenwart von Ca, Ni, Cu und Co bis zum Verhältnis 11 ausgeführt werden. Höhere Konzentrationen an Cu oder Ni können mit KCN maskiert werden, wobei allerdings eine Umkehrung der Kurven auftritt.Ein Verfahren zur Wasserhärtebestimmung mit biamperometrischer Indikation wird vorgeschlagen, das schnell durchzuführen ist und genaue Werte liefert (Fehler ±1%).
Part XV: Vorlíek, J., and P. Peták: Microchem. J. 12, 466–471 (1967). 相似文献