Studies of the naturally occurring biomethylation of selenium and the determination of the products

A systematic study of the biomethylation of selenium and the determination of the methylated species indicates preliminarily that selenium is susceptible to natural biomethylation under certain environmental conditions. Detectable levels of methylated selenium species, including dimethyl selenide [(CH₃)₂Se], dimethyl diselenide [(CH₃)₂Se₂] and dimethylselenone [(CH₃)₂SeO₂] have been detected by gas chromatography – graphite furnace atomic absorption spectrophotometry (GC – GF AA) from a variety of environmental samples. Findings of naturally methylated selenium species from both soil samples and related air samples suggest that there may exist a localized cycle of selenium between ground soil and the ambient air. Factors that influence the sensitivity and accuracy for the determination of alkyl selenide compounds by GC – GF AA have also been investigated. Flashlike injection mode and addition of about 10% of hydrogen gas to the argon carrier gas provide for highly sensitive detection. Reproducible determination can be obtained with a precision of about 6% and the detection limits are 0.3 ng Se m^?3.     

Recent advances in electron-probe x-ray microanalysis

The review covers four main topics: analysis for light elements (Be-F); the use of digital x-ray mapping by wavelength-dispersive x-ray analysis; the use of software for automation of stage and beam control, selective feature analysis, spectrum processing and element identification by the use of expert systems; and the development of quantification models for bulk specimens.     

Secondary-ion mass spectrometry as a quantitative microanalytical technique

Recent progress in ion microscopy and ion-microprobe analysis is reviewed with special emphasis on the potential of the method for the determination of impurities in locally restricted areas of the sample. Emphasis is placed on the calibration of the depth scale and on the potential of the method for three-dimensional analysis.     

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Ohne Zusammenfassung     

Chemical analysis and distribution investigation of trace elements in indium matrix by spark source mass spectrometry

Summary High-purity indium was analysed by spark source mass spectrometry, using electrical and photoplate detection. For the calibration of the differences in elemental sensitivity, a standard sample was prepared in which 10 impurities were determined by graphite furnace atomic absorption spectrometry. In this way accuracies of less than 40% were obtained for relatively homogeneous elements at ppm and sub-ppm level. About 40 elements could be determined with detection limits of 10 to 30 ppb. Two pattern recognition methods, principal component analysis and clustering analysis, were applied to obtain information on trace element distribution, which indicated that a number of elements were strongly spatially correlated in the analysed sample.

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Chemische Analyse und Verteilungsbestimmung von Spurenelementen in Indium-Matrix durch Funkenquellen-Massenspektrometrie

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On leave from: Department of Chemistry, Nanjing Normal University, Nanjing, People's Republic of China     

Metal segregation in bimetallic clusters and its possible role in synergism and bifunctional catalysis

Aspects of the reactivity of segregated bimetallic compounds and their unusual catalytic properties are reviewed with an emphasis on the author's own studies of platinum—ruthenium mixed-metal cluster complexes and their ability to produce hydrogenation and hydrosilylation of alkynes, catalytically.