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71.
Glow discharge mass spectrometry 总被引:5,自引:0,他引:5
Hoffmann V Kasik M Robinson PK Venzago C 《Analytical and bioanalytical chemistry》2005,381(1):173-188
Over the past twenty years or so, glow discharge mass spectrometry (GDMS) has become the industry standard for the analysis of trace elements in metals and semiconductors. A review of its history is followed by a picture of the present situation and a look to where the future may lie. Applications are summarised, including the ability of GDMS to offer depth-resolved data and non-conductor analysis, and the well-documented quantitative nature of the results is reviewed. The effects resulting from the physical properties of the analyte material are discussed at length. Finally, recent work such as fast flow sources and pulsed glow discharges is reviewed. 相似文献
72.
73.
M. E. Niyazymbetov B. Kostizella I. Keitel K. H. Schwartz 《Russian Chemical Bulletin》1991,40(1):182-186
The cathodic electrolysis of aliphatic alcohols and alkylphosphonates in acetonitrile with 0.5 N Et4NClO4 as the base electrolyte leads to mono- and ditransesterified phosphonates. The yield and ratio of these products is a function of the nature of the starting reagents and amount of current passed.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 200–204, January, 1991. 相似文献
74.
75.
Summary A method is proposed for calculating surface selfdiffusion coefficients in sparingly soluble monolayers at fluid interfaces based on radiotracer measurements and allowing for counter geometry. On this basis an analysis of experimental results is possible without having to allow for processes competing with surface self-diffusion. Monolayers of various long-chainn-alcohols andn-alkane-carboxylic acids were studied in the area range between 0.23 nm2/molecule and 2.0 nm2/molecule. Surface self-diffusion coefficientsD
s
were determinded only up to areas of 0.75 nm2/molecule since, in case of greater areas, the analysis of surface concentration becomes inexact due to the increasing influence of density convection. For the systems studied,D
s
values lie in the order of 10–5 cm2/s. In all compounds studied, the values ofD
s
increase with area per molecule. In addition, dependence on the type of hydrophilic group and alkyl-chain length of monolayer molecules was proved. The results are discussed by means of various model concepts.
With 8 figures and 1 table 相似文献
Zusammenfassung Ein Verfahren zur Berechnung der Oberflächenselbstdiffusionskoeffizienten in schwerlöslichere Monoschichten an fluiden Phasengrenzen auf der Grundlage von Radiotracermessungen und unter Berücksichtigung der Zählrohrgeometrie wird vorgeschlagen. Auf dieser Basis ist eine Auswertung der Experimentalergebnisse möglich, ohne daß zur Oberflächenselbstdiffusion in Konkurrenz stehende Transportvorgänge berücksichtigt werden müssen. Untersucht wurden Monoschichten verschiedener längerkettigern-Alkanole undn-Alkancarbonsäuren im Flächenbereich zwischen 0,23 nm2/Molekül und 2 nm2/Molekül. OberflächenselbstdiffusionskoeffizientenD s wurden nur bis zu Flächenwerten von 0,75 nm2/Molekül bestimmt, weil bei höheren Flächen die Auswertung der Oberflächenkonzentrationsänderungen wegen des zunehmenden Einflusses von Dichtekonvektion ungenau wird. DieD s -Werte liegen für die untersuchten Systeme in der Größenordnung 10–5 cm2/s. Bei allen untersuchten Verbindungen nehmen die Werte von Ds mit steigender Fläche pro Molekül zu. Außerdem wurde die Abhängigkeit von der Art der hydrophilen Gruppe und der Alkylkettenlänge der Monoschichtmoleküle nachgewiesen. Die Ergebnisse wurden anhand verschiedener Modellvorstellungen diskutiert.
With 8 figures and 1 table 相似文献
76.
Investigations carried out in order to determine traces of 25 elements in tungsten in the lower g/g range are reported on. Atomic absorption spectrometry and plasma atomic emission spectrometry as well as solution photometry and activation analysis were the main techniques used. 相似文献
77.
The complexing ligand EDTA can be determined as its complex with bismuth by indirect anodic stripping voltammetry down to 0.1 μg/L without a concentration step. Interfering copper and excess bismuth have to be removed by cation exchange, although in presence of these metals EDTA can be determined down to 0.5 μg/L only. If NTA, EDTA, and DTPA are present simultaneously, the accumulation curves for the corresponding bismuth-complexes can overlap, preventing a separate determination of the three chelons. Due to the interaction of NTA and DTPA with soil normally only EDTA is present in ground-waters. Similarly, EDTA also dominates in surface-waters. Thus it seems to be sufficient to determine the sum of the three chelons as EDTA (index of bismuth-complexation) using suitable electrochemical conditions. 相似文献
78.
Robert Martin Nicole Gros Volker Böhmer Hermann Kämmerer 《Monatshefte für Chemie / Chemical Monthly》1979,110(5):1057-1066
TheFries rearrangement of different methoxy benzoates has been investigated. Frompara-methoxy benzoates the corresponding hydroxy-4-methoxy benzophenones could be obtained in good yields by treatment withLewis acids (especially TiCl4) in nitromethane at 20°C (4-hydroxy derivatives) or without solvent at 120°C (2-hydroxy derivatives). Under the same conditions only demethylation occurs withortho-methoxy benzoates leading to the corresponding salicylates. Small amounts of hydroxy-2-methoxy benzophenones were obtained by treatment with polyphosphoric acid. 相似文献
79.
Andreas Stockhammer Klaus-Hermann Dahmen Tobias Gerfin Luigi M. Venanzi Volker Gramlich Walter Fetter 《Helvetica chimica acta》1991,74(5):989-992
The cluster compounds [Pt3(μ-CO)3(PR3)3] act as Lewis bases towards the metal halides of Group XI, MX, Group XII, MX2, and Group XIII, MX3, to form cluster compounds of the composition [{MXn}{Pt3(μ-CO)3(PR3)3}]. The X-ray crystal structure, NMR and IR data are given for the compound [{ZnI}{Pt3(μ-CO)3(PPh(i-Pr)2)3}]. 相似文献
80.
Fausi?RassoulEmail author Heinz?L?ster Volker?Richter 《Monatshefte für Chemie / Chemical Monthly》2005,136(8):1501-1507
Summary. L-Carnitine, L-(−)-β-hydroxy-γ-trimethylaminobutyrate, plays an important role as a factor necessary for the transport of long-chain fatty acids into the mitochondria. In order to investigate the influence of L-carnitine on hyperlipidaemias, the experimental model of the sucrose-induced hypertriglyceridaemia of the rat was used. In these experiments L-carnitine in the dose of 11 mg per day and 100 g body weight (over the period of 1 week) was able to antagonize the sucrose-induced hypertriglyceridaemia and the increase of serum free fatty acid level in female rats of the Wistar strain. Carnitine administration did not change the activities of lipogenic enzymes and fatty acid synthesis in the liver. However, L-carnitine increases the rate of hepatic fatty acid oxidation. Our results indicate a hypotriglyceridemic and free fatty acid lowering effect of L-carnitine, and suggest the use of this compound in the therapy of hyperlipidaemias. 相似文献