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  • 11
    Electronic Resource
    Electronic Resource
    Classification of ancient Roman glazed ceramics using the neural network of Self-Organizing Maps (2000)
    Springer
    Fresenius' journal of analytical chemistry 367 (2000), S. 586-589 
    Details
    ISSN: 1432-1130
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Artificial neural networks with unsupervised learning strategy known as Self-Organizing Maps were applied to classify ancient Roman glazed ceramics. Their clay ceramic bodies were analyzed by Inductively Coupled Plasma-Atomic Emission Spectroscopy and the chemical composition obtained was processed by this neural algorithm. The results obtained provide two types of information: firstly, classification of ceramic samples with identification of several groups and secondly, differentiation between the elemental chemical information. It was found that there are certain chemical elements which can be considered as principal and which can serve to differentiate between ceramics, whereas other elements give redundant information and do not contribute to sample differentiation. Seven chemical elements were considered principal and provide the necessary information. Two types of element were identified: 1 – a group formed by common elements, such as: Ca, Fe, Mg, Mn and 2 – another formed by optional elements: K or Na and Ba or Sr and Al or Ti.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002160000433
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  • 12
    Electronic Resource
    Electronic Resource
    Arsenazo, 2-(4-arsonophenyl(azo-7-(4-antipyril)azo-1,8-dihydroxy-3,6-naphtalene disulphonic acid as reagent for calcium ions. New parameters for metallochromic indicator characterization (1986)
    Springer
    Microchimica acta 88 (1986), S. 73-85 
    Details
    ISSN: 1436-5073
    Keywords: arsenazo ; calcium ; titration ; tristimulus-colorimetry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Ca(II) ions react with arsenazo, 2-(4-arsonophenyl)-azo-7-(4-antipyril)azo-l,8-dihydroxy-3,5-naphtalene disulphonic acid, at pH 10.0 to produce a blue complex, with stoichiometry 1∶1, and stability constant of 6.64×105. Its molar absorptivity is 3.78×1041·mol−1 cm−1. This reagent has been used as metallochromic indicator in the complexometric titration of Ca. Its colour transition has been specified by tristimulus colourimetry. New parameters are defined and compared to Ringbom's parameters.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01196689
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  • 13
    Electronic Resource
    Electronic Resource
    Flame Atomic Absorption Spectrometric Determination of Arsenic After Volatilization of As(III) with Chloride Ions (1999)
    Springer
    Microchimica acta 131 (1999), S. 225-230 
    Details
    ISSN: 1436-5073
    Keywords: Keywords. Arsenic determination; flame atomic absorption; chloride volatilization; insectide sample.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract.  The generation of volatile species of As(III) as a means to introduce arsenic into a flame atomic absorption spectrometer has been studied. The method is based on the reaction between As(III) and chloride ions in sulphuric acid medium. The reaction is performed in a discontinuous or batch mode. With this method 130 μl of a solution containing 17.5% (w/v) sodium chloride and As(III) are injected by a 500 ml.min−1 N2 carrier gas flow into 1 ml of concentrated sulphuric acid. The gaseous compounds generated are introduced into the spectrometer through the nebulizer and As is determined.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/PL00013459
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  • 14
    Electronic Resource
    Electronic Resource
    Determination of As, Sb and Bi in high-purity copper by electrothermal atomic absorption spectrometry (1986)
    Springer
    Microchimica acta 88 (1986), S. 105-114 
    Details
    ISSN: 1436-5073
    Keywords: electrothermal AAS ; copper ; arsenic ; antimony ; bismuth
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract As, Sb and Bi were determined in copper electric cables by atomic absorption spectrometry with electrothermal atomization in a graphite furnace. The interferences in the determination of As, Sb and Bi caused by eleven cationic species and six types of acid were studied. The different volatilization of the copper matrix in comparison to the analyte was studied, as a means of increasing the analyte signal/non-specific absorption signal ratio.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01196692
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  • 15
    Electronic Resource
    Electronic Resource
    Poly(vinyl alcohol) modification with n-alkyl chloroformates (1983)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 112 (1983), S. 205-215 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Die Umsetzung von n-Alkyl-chlorformiat mit Polyvinylalkohol, katalysiert durch Pyridin, wurde untersucht. Die Struktur der modifizierten Polymeren wurde durch IR-, 1H- und 13C-NMR-Spektroskopie und chemische Analysen bestimmt. Es entstehen Vinylalkohol-Vinyl-n-alkylcarbonat-Copolymere. Die Anwesenheit von cyclischen Carbonaten wurde nicht beobachtet. Es wurde eine lineare Abhängigkeit der Reaktionsgeschwindigkeit von den Konzentrationen an Polymerem, n-Alkyl-chloroformiat und Pyridin gefunden. Die Aktivierungsenergie ergab sich zu 15.4 kcal/mol. Das im Copolymeren absorbierte Wasser läßt den Schluß zu, daß der hydrophile Charakter des Copolymeren allmählich abnimmt, wenn der Gehalt an Seitenkettensubstanz steigt. Im Wasser unlösliche Vinyl-alkohol-Vinyl-n-alkylcarbonat-Copolymere wurden in alkalischem Medium hydrolysiert; nach einem bestimmten Hydrolysegrad gewinnen die Polymeren die Wasserlöslichkeit zurück.
    Notes: This work deals with the modification reaction of poly(vinyl alcohol) with n-alkyl chloroformates using pyridine as catalyst. The structure of the modified polymers was determined by means of IR, 1H and 13C-NMR spectroscopy as well as by chemical analysis. Vinyl alcohol-vinyl n-alkyl carbonate copolymers were obtained. The presence of cyclic carbonates has not been observed. It has been found a linear dependence of reaction rate on polymer, n-alkyl chloroformates, and pyridine concentrations, respectively. The activation energy found was of 15.4 kcal/mol. The water absorbed in the copolymers made it reasonable to conclude that the hydrophilic character of the copolymers decreased progressively when either the carbonate groups content or the side chain length increased. Water insoluble alcohol-vinyl n-alkyl carbonate copolymers were hydrolyzed in an alkaline medium. They were found to recover their solubility in water after a certain hydrolysis extent was reached.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1983.051120115
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  • 16
    Electronic Resource
    Electronic Resource
    Kinetic study of the hydrolysis of vinyl alcohol-vinyl n-alkyl carbonate copolymers (1984)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 126 (1984), S. 115-124 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Es wurde die Kinetik der Verseifung von Vinylalkohol-Vinyl-n-alkylcarbonat Copolymeren in Abhängigkeit von der Säure- und Basen-Konzentration, der Temperatur und der Art der Carbonatgruppen untersucht. Die homogene basenkatalysierte Verseifung verläuft nach einer Reaktion erster Ordnung in bezug auf die Hydroxyl-und Carbonatgruppen-Konzentration, während die säurekatalysierte Verseifung in Bezug auf die Säure-Konzentration eine Reaktion erster Ordnung ist. Die heterogene basenkatalysierte Verseifung hängt von der Konzentration und der Art der Carbonatgruppen ab. Für die saure und basische homogene_Verseifung wurden Aktivierungsenergien von 13.8 und 10.0 kcal/mol erhalten. Für die heterogene basenkatalysierte Verseifung ist eine Aktivierungsenergie von 10.3 kcal/mol erhalten worden. α-Chymotrypsin zeigte sich als unwirksam bei den hier durchgeführten Verseifungsreaktionen.
    Notes: A kinetic study of the hydrolysis of vinyl alcohol-vinyl n-alkyl carbonate copolymers has been made as a function of the base or acid concentration, the temperature, and the structure of the carbonate units. The homogeneous hydrolysis in alkaline medium was found to be first order with respect to both the hydroxyl ion and the carbonate; the acid hydrolysis was of first order with respect to the acid concentration. The heterogeneous hydrolysis in alkaline medium followed a pseudo-first-order kinetics with respect to the base concentration; the hydrolysis rate was affected by the carbonate content and the structure of the carbonate units. The activation energies obtained for the acid and base catalyzed homogeneous hydrolysis and the base catalyzed heterogeneous hydrolysis were 13.8, 10.0, and 10.3 kcal/mol, respectively. α-Chymotrypsin was inactive in the hydrolysis experiments carried out with these copolymers.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1984.051260113
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  • 17
    Electronic Resource
    Electronic Resource
    Determination of ytterbium by AES-ICP. Application to samples of biological origin (1988)
    Springer
    Fresenius' Zeitschrift für analytische Chemie 331 (1988), S. 721-724 
    Details
    ISSN: 1618-2650
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Ytterbium is used as a marker in studies of digestion physiology in ruminants; its determination has been accomplished by Inductively Coupled Plasma — Atomic Emission Spectroscopy (ICP-AES). An analytical study has been carried out, which includes the evaluation of various emission lines (atomic, ionic). The line at 328.937 nm is proposed for determining Yb, with a limit of detection of 1.68 ×10−3μg ml−1. The analytical procedure has been applied to the determination of this element in samples of animal fodder, rumen contents and feces.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01105607
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