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101.
A simple and accurate cleanup procedure using polymeric sorbent was developed for the determination of oxytetracycline (OTC) and tetracycline (TC) residues in salmon muscle. It was applied to the analysis of 20 salmon samples during a month period. The OTC and TC residues were extracted with ethylenediaminetetracetic acid (EDTA)-McIlvaine buffer acidified at pH 4.0 and cleaned up by solid-phase extraction with a polymeric sorbent. The advantages of the polymeric sorbent over the silica-based sorbent in the cleanup of salmon muscle samples are described. A liquid chromatographic method with post-column derivatization and fluorescence detection is proposed because of its sensitivity and specificity. The average recoveries of OTC and TC from muscle salmon tissue fortified at 50, 100, and 200 microg/kg levels, ranged from 83.9 to 93.4% with a coefficient of variation between 4.09 and 5.80%. The limit of quantitation for OTC and TC in salmon muscle was 50 microg/kg. 相似文献
102.
Lino Hernández Giuseppe Lubes Mildred Rodríguez Vito Lubes 《Journal of solution chemistry》2012,41(5):840-848
In this study we report the stability constants and the speciation of the ternary vanadium(III) complexes with 2,2??-bipyridine (Bipy) and the amino acids histidine (HHis), cysteine (H2Cys), aspartic acid (H2Asp) and glutamic acid (H2Glu) by means of potentiometric titrations employing 3.0 mol?dm?3 KCl as the ionic medium at 25?°C. The potentiometric data were analyzed taking into account the hydrolysis of the vanadium(III) cation and the respective stability constants of the binary complexes and the acid?Cbase reactions of the ligands, which were kept fixed during the analysis. The complexes detected in the different systems are: in the vanadium(III)?CBipy?CHHis system, [V(HBipy)(HHis)]4+ and [V(HBipy)(H2His)]5+; in the vanadium(III)?CBipy?CH2Cys system, [V2O(Bipy)(Cys)]2+; in the vanadium(III)?CBipy?CH2Asp system, [V(Bipy) (Asp)]+, [V2O(Bipy)(Asp)]2+, and V2O(Bipy)2(Asp)2; and finally in the vanadium(III)?CBipy?CH2Glu system, [V(Bipy)(H2Glu)]3+ and [V(Bipy)(Glu)]+. The respective stability constants were determined and the specie distribution diagrams as a function of pH are briefly discussed. 相似文献
103.
Carl Winstead Qiyan Sun Vincent McKoy Jorge Luiz da Silva Lino Marco A. P. Lima 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1992,24(2):141-147
We present cross sections for the elastic scattering of low-energy electrons by phosphine (PH3) and arsine (AsH3), and for electron-impact excitation of the (1t
2 3sa
1)3
T
2 and1
T
2 states in methane (CH4). These results were calculated using the Schwinger multichannel method as implemented on distributed-memory parallel computers. The PH3 and AsH3 cross sections show a pronounced low-energy shape resonance which may provide a pathway to dissociative attachment. The1,3
T
2 cross sections for CH4 correlate fairly well with recent measurements of CH2 production via electron-impact dissociation of methane.Contribution No. 8587 相似文献
104.
Ricardo J. N. Bettencourt da Silva Maria João Lino Júlia Ribeiro Santos M. Filomena G. F. C. Camões 《Accreditation and quality assurance》2002,7(5):195-201
Food chemical control, particularly control involving the analysis of pesticide residues in fruits and vegetables, is routinely
performed on composite samples. This sample design is adequate for the control of the majority of pesticides which have only
long-term effects. However, from the viewpoint of consumer risk assessment, this sample design is inadequate for pesticides
with relevant acute toxicity, when their residues occur in large food items the consumption of which may represent an important
fraction of a single meal or an important fraction of the consumption in 24 h. This work presents the results of the Portuguese
official pesticide residue control authority concerning the variability of methamidophos concentration in sweet pepper units,
collected from the market, in the framework of the EU 1999 co-ordinated programme for the official control of pesticides in
products of vegetable origin. The results were expressed with uncertainty and the conclusion was that the observed dispersion
cannot be allocated to the method precision. The studied samples presented a variability factor (ratio between the maximum
and the mean concentration of the units) ranging from 1.8 to 3.5 supporting the need to consider a variability factor representing
the potential unit-to-unit variation in residues concentration for the purpose of consumer risk assessment.
Received: 8 December 2001 Accepted: 25 February 2001 相似文献
105.
Enolboronates, new enolates directly accessible from carbonyl compounds and giving aldol products regioselectively and in good yield with aliphatic and aromatic aldehydes, are described. 相似文献
106.
Cesare Gennari Silvia Cardani Lino Colombo Carlo Scolastico 《Tetrahedron letters》1984,25(21):2283-2286
Enolboronates, new enolates directly accessible from carbonyl compounds, exhibit extraordinary high erythro diastereoselection both with aliphatic and aromatic aldehydes. 相似文献
107.
In this paper we study homogeneous curves in generalized flag manifolds with two isotropy summands with the additional property that such curves are geodesics with respect to each invariant metric on the flag manifold. These curves are called equigeodesics. We give an algebraic characterization for such curves and we exhibit families of equigeodesics in several flag manifolds of classical and exceptional Lie groups. 相似文献
108.
109.
This paper presents the new package entitled Simulator of Intelligent Transportation Systems (SITS) and a computational oriented
analysis of traffic dynamics. The SITS adopts a microscopic simulation approach to reproduce real traffic conditions considering
different types of vehicles, drivers and roads. A set of experiments with the SITS reveal the dynamic phenomena exhibited
by this kind of system. For this purpose a modelling formalism is developed that embeds the statistics and the Laplace transform.
The results make possible the adoption of classical system theory tools and point out that it is possible to study traffic
systems taking advantage of the knowledge gathered with automatic control algorithms. A complementary perspective for the
analysis of the traffic flow is also quantified through the entropy measure. 相似文献
110.
The mechanism of the Baeyer-Villiger rearrangement is modelled for the reaction of propanone with trifluoroperacetic acid, catalyzed by trifluoroacetic acid in dichloromethane, using three DFT methods (B3LYP, BH&HLYP and MPWB1K) and MP2. These results are refined and used to calculate the overall reaction rate coefficient using conventional Transition State Theory. The excellent agreement between the calculated (1.00 x 10(-3) L mol(-1) s(-1)) and the experimental (1.8 x 10(-3) L mol(-1) s(-1)) rate coefficients at the MPWB1K level strongly supports the mechanism recently proposed by our group. This DFT method is then used to study the mechanism of a larger system: cyclohexanone + trifluoroperacetic acid, for which a very good agreement between the calculated and the experimental rate coefficients is also found (1.37 and 0.32 L mol(-1) s(-1), respectively). The modelled mechanism is not ionic but neutral, and consists of two concerted steps. The first one is strongly catalyzed while the second one, the migration step, seems not to be catalyzed for the systems under study. The results of this work could be of interest for understanding other reactions in non-polar solvents for which ionic mechanisms have been assumed. 相似文献