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1.
2.
A totally automated and reliable high-performance liquid chromatographic method is described for the routine determination of free catecholamines (norepinephrine, epinephrine and dopamine) in urine. The catecholamines were isolated from urine samples using small alumina columns. A standard automated method for pH adjustment of urine before the extraction step has been developed. The extraction was performed on an ASPEC (Automatic Sample Preparation with Extraction Columns, Gilson). The eluate was collected in a separate tube and then automatically injected into the chromatographic column. The catecholamines were separated by reversed-phase ion-pair liquid chromatography and quantified by fluorescence detection. No manual intervention was required during the extraction and separation procedure. One sample may be run every 15 min, ca. 96 samples in 24 h. Analytical recoveries for all three catecholamines are 63-87%, and the detection limits are 0.01, 0.01, and 0.03 microM for norepinephrine, epinephrine and dopamine, respectively, which is highly satisfactory for urine. Day-to-day coefficients of variation were less than 10%. 相似文献
3.
By quenching into the metastable region of the three-dimensional Ising model, we investigate the paths that the magnetization (energy) takes as a function of time. We accumulate the magnetization (energy) paths into time-dependent distributions from which we reconstruct the free energy as a function of the magnetic field, temperature, and system size. From the reconstructed free energy, we obtain the free-energy barrier that is associated with the transition from a metastable state to the stable equilibrium state. Although mean-field theory predicts a sharp transition between the metastable and the unstable region where the free-energy barrier is zero, the results for the nearest-neighbor Ising model show that the free-energy barrier does not go to zero. 相似文献
4.
A new general synthesis of 4,5-disubstituted 2,4-dihydro-1,2,4-triazole-3-thiones is proposed. These heterocycles are obtained by the action of primary amines, arylhydrazines or aroylhydrazines on the thiosemicarbazones of eaters. These last compounds are prepared by action of chlorhydrates of iminoethers on thiosemicarbazide in dimethylformamide. These thiosemicarbazones react also with strong acids, acid anhydrides and chlorides; by thermolysis and they give 2-amino-1,3,4-thiadiazole derivatives. Also, two derivatives of 1,2,4-triazolo[3,4-b]-1,3,4-thiadiazole have been prepared. 相似文献
5.
Michle Philoche-Levisalles Claudette Bois Jean-Pierre Clrier Grard Lhommet 《Journal of heterocyclic chemistry》1982,19(3):481-484
The structure of ethyl α-(tetrahydro-2-pyrrolidinylidene) and α-(hexahydro-2-azepinylidene) acetates has been determined from the X-ray crystallographic analysis. The results show that, in a solid state, these compounds exist as β-enaminoesters which have a Z configuration. They also show the presence of intra and intermolecular hydrogen bonding. 相似文献
6.
Résumé Un calcul complet de constantes de couplage nucléaires J
HH, J
XH et J
XX (X = C, N, P) a été fait pour une série de molécules organiques dont les fonctions LCAO SCF MO exactes sont connues. L'influence de la charge nucléaire efficace des orbitales atomiques de base a été étudiée dans le cas particulier du méthane et de l'éthane. La décomposition des constantes de couplage en éléments de symétrie est employée pour la comparaison des résultats théoriques et expérimentaux.
Numerical calculations of spin-spin coupling constants with exact LCAO SCF MO functions
Complete calculations of nuclear spin-spin coupling constants J HH, J XH and J XX (X = C, N, P) have been carried out for some organic molecules the exact LCAO SCF MO functions of which are known. The results obtained using atomic basis sets with different orbital exponents are discussed in the case of methane and ethane. Theoretical values are compared to experimental data in terms of components arising from the symmetry analysis of actual coupling constants.
Zusammenfassung VollstÄndige Berechnungen der Spin-Spin-Kopplungskonstanten J HH, J XH und J XX (X = C, N, P) werden für einige organische Moleküle durchgeführt, deren genaue LCAO-SCF-MO-Funktionen bekannt sind. Der Einflu\ der effektiven Kernladungszahlen der Basisfunktionen wurde im Falle von Methan und Äthan untersucht. Die theoretischen und experimentellen Werte werden nach ihrer Zerlegung in Symmetriekomponenten miteinander verglichen.相似文献
7.
Marcellino S Attar H Lièvremont D Lett MC Barbier F Lagarde F 《Analytica chimica acta》2008,629(1-2):73-83
An analytical method was developed for antimony speciation and antimony(III) preconcentration in water samples. The method is based on the selective retention of Sb(III) by modified Saccharomyces cerevisiae in the presence of Sb(V). Heat, caustic and solvent pretreatments of the biomass were investigated to improve the kinetics and thermodynamics of Sb(III) uptake process at room temperature. Heating for 30 min at 80 degrees C was defined as the optimal treatment. Antimony accumulation by the cells was independent of pH (5-10) and ionic strength (0.01-0.1 mol L(-1)). 140 mg of yeast and 2h of contact were necessary to ensure quantitative sequestration of Sb(III) up to 750 microg L(-1). In these conditions, Sb(V) was not retained. Sb(V) was quantified in sorption supernatant by inductively coupled plasma mass spectrometry (ICP-MS) or inductively coupled plasma optical emission spectrometry (ICP-OES). Sb(III) was determined after elution with 40 mmol L(-1) thioglycolic acid at pH 10. A preconcentration factor close to nine was achieved for Sb(III) when 100mL of sample was processed. After preconcentration, the detection limits for Sb(III) and Sb(V) were 2 and 5 ng L(-1), respectively, using ICP-MS, 7 and 0.9 microg L(-1) using ICP-OES. The proposed method was successfully applied to the determination of Sb(III) and Sb(V) in spiked river and mineral water samples. The relative standard deviations (n=3) were in the 2-5% range at the tenth microg L(-1) level and less than 10% at the lowest Sb(III) and Sb(V) tested concentration (0.1 microg L(-1)). Corrected recoveries were in all cases close to 100%. 相似文献
8.
Catalytic wet air oxidation of oleic acid on ceria-supported platinum catalyst.effect of pH 总被引:1,自引:0,他引:1
Beno?t Levasseur Benoist Renard Jacques Barbier Jr. Daniel Duprez 《Reaction Kinetics and Catalysis Letters》2006,87(2):269-279
Summary Catalytic wet air oxidation (CWAO) of oleic acid was carried out in a batch reactor on platinum supported ceria catalyst (Pt/CeO2). Oleic acid is a water insoluble linear unsaturated fatty acid of 18 carbon atoms. To increase the homogeneity of the solution
by saponification, the influence of NaOH additions in oleic acid CWAO mechanism and catalyst performances have been investigated.
The oxidation of such molecule occurs by two types of mechanisms: successive carboxy-decarboxylation which leads essentially
to CO2and/or C-C bonds splitting in the alkyl chain inducing a high formation of acetic acid. With or without NaOH, the 5%Pt/CeO2catalyst is active in the conversion of oleic acid and selective to carbon dioxide. In alkaline medium, oleic acid is initially
saponified which increases the solubility of the reactant before it to be oxidized. Finally the oxidation is slightly delayed
by the presence of NaOH. The catalyst characterizations show no significant difference before and after reaction.</o:p> 相似文献
9.
Using a perturbational configuration interaction approach, it is found that the Fe-CO molecule has a low-spin ground state (i.e. 3–), at variance with similar compounds formed by the first transition elements of this series (e.g. Sc and Ti). Binding energies, interatomic distances and vibration frequencies have been calculated for the 3– state as well as for the 5– high-spin state.Dedicated to Professor J. Koutecký on the occasion of his 65th birthday 相似文献
10.
Wang Mei Miguel Daniel Riera Víctor Bois Claudette Jeannin Yves 《Transition Metal Chemistry》2001,26(4-5):566-569
A novel dimolybdenum complex [(3-C3H5)(CO)2Mo(-S2CPCy3)Mo(3-CH2CMeCH2)(CO)2], obtained by reacting the [(CO)2(3-C3H5)Mo(-S2CPCy3)Mo(CO)3]– anion with an excess of ClCH2CMe=CH2, has been characterized by i.r., 31P{1H}, 1H- and 13C-n.m.r. spectroscopy and by elemental analysis. The crystal structure of the complex, determined by X-ray diffraction, shows a definite preference for the central carbon of the S2CPCy3 bridge to bind to the Mo(2) atom coordinated by 3-2-methylallyl, rather than the Mo(1) atom attached to unsubstituted 3-allyl ligand. 相似文献