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1.
Jochum KP Stoll B Pfänder JA Seufert M Flanz M Maissenbacher P Hofmann AW Hofmann AW 《Fresenius' Journal of Analytical Chemistry》2001,370(5):647-653
Spark source mass spectrometry (SSMS) has experienced important and significant improvements in nearly all analytical features by the use of a multiple ion counting (MIC) system. Two procedures have recently been developed to further increase the analytical capabilities of MIC-SSMS in geochemistry. These are a mathematical correction of interferences, which is often necessary for the ultra trace element analysis of Nb, Ta, Zr, Hf and Y, and the development of an autospark system to hold the total ion beam constant. New analytical data for geological samples, especially international reference materials, are presented using the improved MIC-SSMS technique. The data set consists of high precision and low abundance data for Zr, Nb and Y in depleted reference materials. The MIC-SSMS results are compared with those of conventional SSMS using photoplates for ion detection. The precision of the MIC-SSMS isotope ratio measurements (about 1%) is more than a factor of 3 better than that of conventional SSMS, as demonstrated by analyses of Hawaiian samples. Total uncertainties of MIC-SSMS concentration data including all sources of error are generally between 2 and 5% for concentrations higher than about 0.3 microg/g and about 10% for trace element abundances in the ng/g range. 相似文献
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Prof. Dr. K. -H. Hellwege U. Johnsen Dipl.-Phys. W. Seufert 《Colloid and polymer science》1963,188(1):11-14
Zusammenfassung PÄT-Folien wurden in Luft, Stickstoff und Vakuum bei 20 °C mit 1 MeV-Elektronen bestrahlt. Untersucht wurden Löslichkeit und Viskosität von Proben, die unmittelbar nach der Bestrahlung gelöst wurden.In allen untersuchten Fällen trat bei hohen Bestrahlungsdosen ein unlöslicher, d. h. vernetzter Anteil auf, dessen Ausbildung jedoch durch in den Proben enthaltene Feuchtigkeit verzögert werden kann. Bei niedrigen Bestrahlungsdosen bewirkt Feuchtigkeit einen Abbau des Polymeren, wie durch Viskositätsmessungen gezeigt wird.Aus den Gel-Messungen wurde derp
0/q
0-Wert für Bestrahlung in Luft, Stickstoff und Vakuum zu 1,05 bestimmt.Die Änderung des Gel-Anteils bei Lagerung der Proben zwischen Bestrahlung und Lösung wird diskutiert.
Herrn Diplom-PhysikerH. Fischer sei an dieser Stelle für wertvolle Anregungen und Diskussionen besonders gedankt. 相似文献
Summary Polyethyleneterephthalate samples were irradiated in air, nitrogen and vacuum at 20 °C with 1 MeV electrons. The solubility of the samples and the viscosity of the solutions were studied immediately after irradiation. At high doses an insoluble crosslinked part was always observed. Crosslinking was delayed by moisture in the samples. At low irradiation doses moisture causes chain scission as shown by viscosity measurements. The ratiop 0/q 0 of degradation to crosslinking in the case of irradiation in air, nitrogen and vacuum was found by gel measurements to be 1.05. The insoluble gel-part changes with increasing storage time of the samples between irradiation and solution.
Herrn Diplom-PhysikerH. Fischer sei an dieser Stelle für wertvolle Anregungen und Diskussionen besonders gedankt. 相似文献
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A new spark source mass spectrometric technique for the analysis of sub-ng amounts of trace elements
A. Rocholl K. P. Jochum H. M. Seufert S. Midinet-Best 《Fresenius' Journal of Analytical Chemistry》1988,331(2):140-144
Summary Spark source mass spectrometric tip-top-technique (TTT) is a new method for the analysis of sub-ng amounts of chemically separated trace elements in geological material. Besides its application to dissolved samples, TTT differs from conventional spark source mass spectrometry in reduction of measuring time (few minutes), photoplate background, and interferences by isobars and cluster-ions, resulting in enhanced sensitivities. Detection limits range from about 5 to 20 pg for the rare earth elements, U and Th, and from about 10 to 100 pg for noble metals. Precisions and accuracies of 1 to 5% are gained for trace elements abundances about 1 ng.A potential and especially useful application of TTT is the analysis of rocks available only in very small sample sizes and/or with very low concentration levels of trace elements. An additional application is the determination of osmium isotopes in geological material.
Neues funkenmassenspektrometrisches Verfahren für die Analyse von sub-ng-Mengen von Spurenelementen相似文献
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Niederdraenk F Seufert K Stahl A Bhalerao-Panajkar RS Marathe S Kulkarni SK Neder RB Kumpf C 《Physical chemistry chemical physics : PCCP》2011,13(2):498-505
The detailed structural characterization of nanoparticles is a very important issue since it enables a precise understanding of their electronic, optical and magnetic properties. Here we introduce a new method for modeling the structure of very small particles by means of powder X-ray diffraction. Using thioglycerol-capped ZnO nanoparticles with a diameter of less than 3 nm as an example we demonstrate that our ensemble modeling method is superior to standard XRD methods like, e.g., Rietveld refinement. Besides fundamental properties (size, anisotropic shape and atomic structure) more sophisticated properties like imperfections in the lattice, a size distribution as well as strain and relaxation effects in the particles and-in particular-at their surface (surface relaxation effects) can be obtained. Ensemble properties, i.e., distributions of the particle size and other properties, can also be investigated which makes this method superior to imaging techniques like (high resolution) transmission electron microscopy or atomic force microscopy, in particular for very small nanoparticles. For the particles under study an excellent agreement of calculated and experimental X-ray diffraction patterns could be obtained with an ensemble of anisotropic polyhedral particles of three dominant sizes, wurtzite structure and a significant relaxation of Zn atoms close to the surface. 相似文献
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Jonas H. Muessig Melanie Thaler Rian D. Dewhurst Valerie Paprocki Jens Seufert James D. Mattock Alfredo Vargas Holger Braunschweig 《Angewandte Chemie (International ed. in English)》2019,58(13):4405-4409
The lability of B=B, B?P, and B–halide bonds is combined in the syntheses of the first diiododiborenes. In a series of reactivity tests, these diiododiborenes undergo cleavage of all six of their central bonds in different ways, leading to products of B=B hydrogenation and dihalogenation as well as halide exchange. 相似文献
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Jens Seufert Eileen Welz Dr. Ivo Krummenacher Valerie Paprocki Julian Böhnke Stephan Hagspiel Dr. Rian D. Dewhurst Prof. Dr. Reinhold Tacke Prof. Dr. Bernd Engels Prof. Dr. Holger Braunschweig 《Angewandte Chemie (International ed. in English)》2018,57(33):10752-10755
Diaryldihalodiboranes(4) were reacted with bis(amidinato)‐ and bis(guanidinato)silylenes to generate the first neutral diborane‐centered radicals. These formally non‐aromatic 5π electron systems are stable in the solid state as well as in solution and were characterized by solid‐state structure determination, high‐resolution mass spectrometry, and EPR spectroscopy. The reactivity of one of these radicals with the oxidant 1,4‐benzoquinone led to ring‐opening and B?O bond formation. 相似文献
10.
Bis(trimethylsilyl)cyclopentadiene reacts with two equivalents of boron halides to the bis(dihalogenoboryl)cyclopentadienes I, II and III. Reactions of I, II and III with tetramethyltin and dimethylamine yield the dimethyl- and bis(dimethylamino)-substituted compounds IV and V. The fluoro compound VI is synthesized by the reaction of III with arsenic trifluoride. Addition of pyridine to I and II yields the adducts VII and VIII. Structure and bonding properties of I–VIII are discussed by 1H-, 13C-, 11B- and 19F.n.m.r- and by i.r. and m.s. data. 相似文献