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491.
Application of inductively coupled plasma sector field mass spectrometry (ICP-SFMS) for the determination of americium and plutonium in environmental samples is described in comparison with alpha spectrometry. A sequential sample preparation method was employed using a co-precipitation step for pre-concentration and a separation step applying extraction chromatographic resins. The average recovery of sample preparation calculated from the concentration of the tracer before and after sample treatment was better than 80%. The method development focused on the elimination of possible interferences in mass spectrometric analysis caused by molecular ions (e.g. 200Hg40Ar+, 204Pb36Ar+, 208Pb16O2+or 238U1H+) employing matrix separation and desolvation prior to ICP-SFMS analysis. The effect of N2 gas on signal intensity and oxide ratio was investigated. A two-fold signal improvement was obtained by adding 5 ml min− 1 N2 to the sample gas after the desolvation system. For 239Pu, 240Pu, 241Pu and 241Am limit of detection (LOD) of 15, 9.2, 14 and 104 fg g− 1 was achieved, respectively. Calculation of LOD was based on three times standard deviation of the method blank solution. Absolute detection limit was calculated to be 10-25 fg. For all investigated actinides the precision of the analysis was in the range 0.8-3% relative standard deviation. Results from the analysis of certified reference materials (IAEA-384 and IAEA-385) showed good agreement with recommended values and data available in the literature. The method was applied for analysis of environmental samples originated from Chernobyl and from Mayak region. The possibility of the determination of the origin and date of pollution was demonstrated using isotopic data obtained by ICP-SFMS and alpha spectrometry. 相似文献
492.
Synthesis of a N-Boc-protected piperidin-2-yl phosphine oxide starting from piperidine in three steps, followed by olefination using a variety of α,β-unsaturated aldehydes resulted in tert-butyl 2-(2′-alkenylidene)piperidine-1-carboxylates in high yields. A novel type of intramolecular cyclization of these enamides furnished a new family of 3-alkyl-4,6,7,8-tetrahydro-3H-pyrido[1,2-c][1,3]oxazin-1-ones as useful substrates for further elaboration. Subsequent reduction of these unsaturated bicyclic carbamates using NaCNBH3 or NaBH4 afforded the corresponding 3-alkylhexahydropyrido[1,2-c][1,3]oxazin-1-ones in a highly stereoselective way. Reductive ring opening of two representatives furnished the corresponding Sedum alkaloid derivatives in good yields. 相似文献
493.
A simultaneous multi-elemental measurement of As, Bi, Ge, Sb, Se, and Sn was performed in this study by flow injection-hydride generation-inductively coupled plasma-time-of-flight mass spectrometry (FI-HG-ICP-TOFMS). An off-line pre-reduction treatment using a solution of 5% (m/v) KI and ascorbic acid for 15 min at 80 °C is described by presenting its advantages and disadvantages and compared with the results achieved without pre-reduction. Using optimised conditions the following figures of merit were achieved: limits of detection in the 0.08-0.54 ng ml−1 range and relative standard deviations (RSD) of 1.7-6.7%, respectively. Applying the presented method, two certified reference materials (NIST 1643d freshwater and PACS-2 marine sediment) were analysed to demonstrate the suitability of the method for analysis of real samples. Results obtained from treated samples showed good agreement with certified values while the untreated ones considerably departed from them. 相似文献
494.
Ferenc Joó Sándor Benk Ibolya Horváth Zsolt Török Levente Nádasdy László Vígh 《Reaction Kinetics and Catalysis Letters》1992,48(2):619-625
Colloidal palladium anchored onto the surface of insoluble polyvinyl-polypirrolidone (Pd-PVPP) is anactive, non-permeable catalyst for surface selective hydrogenation of model or isolated biomembranes.
, , , .相似文献
495.
Bodó ET Stefánka Z Ipolyi I Sörös C Dernovics M Fodor P 《Analytical and bioanalytical chemistry》2003,377(1):32-38
A laboratory reference material (LRM) was prepared from Brazil nuts (Bertholletia excelsa) for quality control (QC) purposes of selenium speciation. The preparation of this LRM led through the usual operation steps applied during routine reference material production from biota samples-preparation of the raw material, homogenisation, storage design, checking of homogeneity, microbiological status and possible irradiation effects, and monitoring the species stability vs time at different storage temperatures. The selenium speciation studies to check species stability were carried out on a HPLC-UV-HG-AFS measurement set-up. Special attention was paid to the correct identification of selenium species by applying independent HPLC separation techniques (ion-pairing and anion-exchange chromatography). The concentration of selenomethionine (SeMet) and total Se content were quantified (79.9 microg g(-1) (calculated as Se) and 82.9 microg g(-1), respectively). The homogeneity and stability of this candidate reference material passed the relevant tests recommended by Bureau Communautaire de Référence (BCR). 相似文献
496.
Zsolt Tuza 《组合设计杂志》1995,3(2):89-99
Proving a conjecture of Aigner and Triesch, we show that every graph G = (V,E) without isolated vertices and isolated edges admits an edge labeling ξ: E → {0,1}m with binary vectors of length m = [log2 n] + 1 such that the sums. CALLING STATEMENT : (taken modulo 2 componentwise) are mutually distinct, provided that n is sufficiently large. The proof combines probabilistic arguments with explicitly constructed Steiner systems. © 1995 John Wiley & Sons, Inc. 相似文献
497.
Zsolt Tuza 《Graphs and Combinatorics》1991,7(1):89-93
Upper and lower bounds are given for the minimum number of perfect (induced or partial) subgraphs covering or partitioning the vertex set or the edge set of a graph ofn vertices. Also, weighted versions of the problems are investigated.Research supported in part by the OTKA Research Fund of the Hungarian Academy of Sciences, Grant No. 1812. 相似文献
498.
Karoly Bezdek Zsolt Langi Marton Naszodi Peter Papez 《Discrete and Computational Geometry》2007,38(2):201-230
We study two notions. One is that of spindle convexity. A set of circumradius not greater than one is spindle convex if, for
any pair of its points, it contains every short circular arc of radius at least one, connecting them. The other objects of
study are bodies obtained as intersections of finitely many balls of the same radius, called ball-polyhedra. We find analogues
of several results on convex polyhedral sets for ball-polyhedra. 相似文献
499.
500.
Zsolt Patakfalvi 《Discrete Mathematics》2008,308(12):2351-2365
A graph is called normal if its vertex set can be covered by cliques Q1,Q2,…,Qk and also by stable sets S1,S2,…,Sl, such that Si∩Qj≠∅ for every i,j. This notion is due to Körner, who introduced the class of normal graphs as an extension of the class of perfect graphs. Normality has also relevance in information theory. Here we prove, that the line graphs of cubic graphs are normal. 相似文献