The accurate determination of cobalt: Gravimetric methods and in particular the phosphate method

Some gravimetric methods for determining cobalt have been examined in order to assess their value for the accurate determination of the metal. The electrolytic method was found to give high results (about 1.4%), and the anthranilate method slightly high results (0.2 – 0.3%). A modification of the phosphate method has been developed in which a former drawback, the solubility of CoNH₄PO₄·H₂O, has been overcome using a rapid spectrophotometric determination of residual cobalt. The final procedure developed has been found to give accurate results ( ±0.1 – 0.2%) and its use is recommended where this degree of accuracy is required.     

Photoelectron spectroscopy of phosphorus hydride anions

Negative-ion photoelectron spectroscopy is applied to the PH-, PH2-, P2H-, P2H2-, and P2H3-molecular anions. Franck-Condon simulations of the photoelectron spectra are used to analyze the spectra and to identify various P2H(n)- species. The simulations employ density-functional theory calculations of molecular geometries and vibrational frequencies and normal modes, and coupled-cluster theory calculations of electron affinities. The following electron affinities are obtained: EA0(PH) = 1.027 +/- 0.006 eV, EA0(PH2) = 1.263 +/- 0.006 eV, and EA0(P2H) = 1.514 +/- 0.010 eV. A band is identified as a mixture of trans-HPPH- and cis-HPPH-. Although the trans and cis bands cannot be definitively assigned from experimental information, using theory as a guide we obtain EA0(trans-HPPH)= 1.00 +/- 0.01 eV and EA0(cis-HPPH) = 1.03 +/- 0.01 eV. A weak feature tentatively assigned to P2H3- has a vertical detachment energy of 1.74 eV. The derived gas-phase acidity of phosphine is delta(acid)G298(PH3) < or = 1509.7 +/- 2.1 kJ mo1(-1).     

Determination of methadone and its metabolites by high performance liquid chromatography following solid-phase extraction in rat plasma.

This paper describes a rapid, quantitative liquid chromatographic analysis and extraction of methadone and its two major metabolites from rat plasma, using difenoxin as the internal standard. Using a C18 column, resolution of all sample components and the internal standard is achieved with a mobile phase of 25:75 acetonitrile-0.08% diethylamine in 1000 mL water, pH 2.3, at a flow rate of 1.5 mL/min. The injection volume is 100 microL. Standards are linear over the range 25-100 ng, with a lower limit of detection for methadone of 0.25 ng. Within- and between-run coefficients of variation (CV) are 1.24% and 2.94%, respectively. Extraction of methadone and its metabolites from rat plasma uses a solid-phase extraction technique that is highly efficient. Extraction efficiencies of 90.3%, 99.6%, 85.9% and 93.8% were achieved for methadone, its primary and secondary metabolites, and difenoxin, respectively.     

Immunochemical detection of aminoglycosides in milk and kidney

In 1996, the European Union established provisional maximum residue limits (MRL) for gentamicin, neomycin, streptomycin and dihydrostreptomycin in milk and tissue (0.1-5 mg kg-1). For the detection of these four aminoglycosides, three enzyme linked immunosorbent assays (ELISA) for applications in milk and kidney were developed. The screening of defatted and diluted milk resulted in limits of determination (LDM) of < 0.01 mg l-1. Kidney samples were deproteinized with a trichloroacetic acid solution (3%) and after filtration and the addition of buffer, aliquots were used in the ELISA. The LDM of the four aminoglycosides in kidney were < 0.05 mg kg-1. The ELISA were found suitable for the semi-quantitative screening of milk and kidney for the presence of the four aminoglycosides far below the MRL levels. In randomly taken milk samples (n = 776) and in kidneys derived from healthy pigs (n = 124), the aminoglycoside residues found were far below their established MRL. In eight out of the 94 kidney samples obtained from diseased animals after emergency slaughter, aminoglycoside residues were above the MRL.     

Sequence distribution and intramolecular excimer formation in styrene-acrylonitrile copolymers

Styrene-acrylonitrile copolymers, like many other copolymers containing styrene, exhibit both normal and excimer fluorescence. We have shown that the ratio of the excimer to monomer fluorescence intensities in random styrene-acrylonitrile copolymers is linearly dependent upon the concentration of styrene-styrene bonds in the copolymer. This observation is consistent with a photophysical model which allows the energy absorbed by styrene units to migrate freely along the copolymer chain. Some of the energy is emitted in the form of normal fluorescence; some of the energy, trapped by neighbouring styrene-styrene pairs suitably oriented to allow excimer formation, is emitted as excimer fluorescence. The fluorescence characteristics of acrylonitrile-styrene copolymers are contrasted with those of methyl methacrylate-styrene copolymers, in which the methylmethacrylate sequences are believed to present partial barriers to energy migration along the copolymer chains.     

Luminescence characteristics of several classes of drugs affecting the central nervous system

The excitation, fluorescence and phosphorescence characteristics of 29 compounds of psychopharmacological interest have been studied in ethanol at 77 k. Phosphorescence lifetimes are reported and the low-temperature luminescence spectra discussed. Luminescence characteristics of several important 1,4-benzodiazepines in acidic, basic and neutral solution are reported.     

Theoretical analysis of the electronic structure and molecular properties of thioborine,HSB and comparison with related compounds. An ab initio mo-cal

Ab initio calculations on the thioborine molecule have been performed. Ionization potentials, force constants and geometry parameters are calculated in fair agreement with experimental values. A preliminary investigation of the sensitivity by nucleophilic attack has also been performed, indicating a rather strong tendency to undergo that type of reaction.     

On the loss of cadmium, antimony and silver during dry ashing of biological material

Summary The loss of cadmium, antimony and silver during dry ashing of marine weeds, mussels and shrimps was studied with the aid of radioactive tracers. Except for antimony all biological material was labelled by uptake of the radioactive tracers by the organisms while still alive. At an ashing temperature of 500° C and below no significant loss by volatilization of these elements occurs. The results obtained at higher temperatures with cadmium show that the behaviour of this element may depend on the composition of the organic material. Retention on the wall of quartz crucibles did not cause serious losses.

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Über den Verlust an Cadmium, Antimon und Silber bei der Trockenveraschung von biologischem Material

Zusammenfassung Mit Hilfe radioaktiver Tracer wurden die Verluste an Cadmium, Antimon und Silber bei der Trockenveraschung von Seetang, Muscheln und Krabben untersucht. Mit Ausnahme von Antimon wurden alle Materialien mit den Tracern durch Aufnahme im lebenden Zustand markiert. Bei Veraschungstemperaturen von 500° C und darunter konnten keine signifikanten Verluste durch Verflüchtigung der Elemente festgestellt werden. Das Verhalten von Cadmium bei höheren Temperaturen kann von der Zusammensetzung des organischen Materials abhängen. Verluste durch Haften an der Wand des Quarztiegels waren unbedeutend.

     

Syntheses and degradations of fluorinated heterocyclics III. Perfluoroalkyl and perfluoroalkylether-1,3,4-oxadiazoles

2,5-Bis(perfluoro-n-heptyl)-, 2-perfluoroalkylether-5-perfluoro-n-heptyl-, and 2,5-bisperfluoroalkylether-1,3,4-oxadiazoles were synthesized and characterized. 2,5-Bis(perfluoro-n-heptyl)-1,3,4-oxadiazole was thermally and hydrolytically stable at 325°C; however, in the presence of air, degradation took place at 235°C. The perfluoroalkylether analogue exhibited thermal and hydrolytic stability at 325°C; it was found to be unaffected by Jet-A fuel and air at 235°C. At 325°C in air some degradation occured as evidenced by volatiles production, oxygen consumption, and 96% starting material recovery.     

X-ray diffraction and morphology of crystalline,hard, elastic materials

Summary X-ray diffraction and electron microscopic results on several crystalline polymers which demonstrate elastic properties (polypropylene, Celcon^®, poly-4-methyl-pentene) are reported. Photographic small angle X-ray diffraction techniques provided considerable qualitative information, concerning the morphological features of these elastic materials both as extruded, annealed and during extension. Lamellar thickness, thickness distribution and perfection of lamellae could be estimated. Lateral order features and orientation of the lamellar structures were obtainable from the sharpness and length of the equatorial wide angle diffraction arcs. Electron microscopic results essentially confirm the morphological features postulated on the basis of the X-ray results. These morphological features are discussed in terms of a general structural model which appears consistent with the mechanical properties of these materials.

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Zusammenfassung Röntgenbeugung und elektronenmikroskopische Daten von einigen kristallinen Polymerprodukten mit elastischen Eigenschaften (Polypropylen, Celcon, Poly-4-methylpenten) werden berichtet. Die photographische Röntgen-Kleinwinkelmethode liefert wichtige qualitative Messungen der morphologischen Struktur dieser elastischen Materialien in den Zuständen sowohl wie hergestellt als auch nach Tempern und während des Dehnungsprozesses. Die Dicke der Lamellen, ihre Dikkenverteilung und die Güte der Lamellen konnten abgeschätzt werden. Die laterale Ordnung und die Orientierung der Lamellen kann aus Weitwinkelbeugungsdaten abgeleitet werden. Die Elektronenmikroskopie bestätigt die Morphologie, die aus Röntgendaten folgt. Ein allgemeines Strukturmodel dieser Morphologie, das im Einklang mit den mechanischen Eigenschaften dieser Produkte steht, wird diskutiert.