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11.
An automatic continuous-flow photometric method for the determination of ammonia is proposed. It is based on the Berthelot reaction, the product of which is temporarily immobilized on a suitable support (Sephadex QAE) located in the flow-cell. The retained product is eluted after measurement by a cationic surfactant contained in the carrier solution. The method allows the determination of the analyte between 0.4 and 20.0 gmg/ml, with an RSD of 0.8%, at a sampling frequency of 13/hr. The determination limit can be reduced by a factor of ten by using a flow-cell with a two-fold longer path length, but the sampling frequency is also reduced as a result. The method was applied to the determination of this analyte in agricultural samples (plants and soils) and compared with standard methods for these types of samples. 相似文献
12.
The effects of temperature and duration of melting on the rate of isothermal crystallization of isotactic polypropylene were investigated by differential scanning calorimetry (DSC). Crystallization rates were found to decrease with increasing melt temperature and melting time. The results were discussed in the framework of the theoretical model of transient isothermal crystallization developed by the present authors [1]. The results suggest gradual destruction of predetermined nuclei with activation energyE
a=89±7 kJ/mole as a main mechanism of the observed effects.This work and Part I of this research [1] have been supported in part by Research Grant Number PB 1291/52/93/04 from State Committee for Scientific Research (KBN), Poland, and by 40% MURST founds, Italy. 相似文献
13.
O. G. Stradella S. A. Maluendes E. A. Castro A. H. Jubert 《Theoretical chemistry accounts》1987,72(1):57-62
By means of Bader's approach on topological properties of the electronic density, the major stability of the O-bonded adduct over the C-bonded one between MgF2 and CO is reinforced. 相似文献
14.
A simple spectrofluorimetric method for the determination of the fungicide benomyl in grapes is described. Benomyl is rapidly solvolysed in organic solvents to give the highly fluorescent metabolite carbendazim. Solvent effects on the spectral shape and their influence on analytical performance are studied. DMF was found to be the best solvent. The method is sensitive to 12 ng/ml benomyl, and has an RSD at the 0.5 g/ml level of 2.2%. The method is suitable for determining benomyl in spiked grapes, with recoveries in the range 97 to 104%. 相似文献
15.
Aurora Molinari Alfonso Oliva Luc Snchez Arturo San Feliciano 《Journal of heterocyclic chemistry》1997,34(4):1297-1299
1-Phenyl-3,5-dioxopyrazolidine 1 reacts with carbon disufide and alkyl halides in presence of excess of sodium acetate in dimethylformamide to afford the ketene dithioacetals 3a-h . The 13C chemical shift assignments of these compounds were made on the basis of two-dimensional nmr studies performed on the N-methylketene dithioacetal derivative 4. 相似文献
16.
Norman S. Allen Alfonso Chirinos-Padron John H. Appleyard 《Polymer Degradation and Stability》1982,4(3):223-237
The photo-stabilising action of three metal chelates—nickel (II) 2,2′ thiobis (4-tert-octylphenylato) n-butylamine and the nickel and calcium derivatives of bis (ethyl-3,5-di-tert-butyl-4-hydroxybenzyl) phosphonate, in polypropylene—is examined using normal and second order derivative ultraviolet, infra-red and phosphorescence spectroscopic techniques and hydroperoxide analysis. Whilst all three stabilisers quenched the phosphorescence emission of a powerful photo-sensitiser, benzophenone, there was no protective action during photo-sensitised oxidation of the polymer. In the case of anthraquinone, there was no quenching and no protection. Processing history plays a dominant rôle in controlling the photo-stabilising performance of the chelates. Each stabiliser operates differently, being dependent on its relative stability during processing and photo-oxidation and on the formation and destruction of polymeric and antioxidant hydroperoxides during processing. Metal chelates operate by inhibiting polymer hydroperoxide formation during processing and acting as ultraviolet stable chain terminators or by giving products during the early stages of photo-oxidation which are themselves effective stabilisers. 相似文献
17.
Zareen Ahkter Andrew J. Edwards Scott L. Ingham Jack Lewis Ana M. Martin Castro Paul R. Raithby Gregory P. Shields 《Journal of Cluster Science》2000,11(1):217-226
The reaction of the di-gold cation [Au2(dppx)]2+ with the heptanuclear cluster dianion [Os7(CO)20]2– affords the mixed metal cluster [Os7(CO)20{Au2(dppx)}] (x=m (1), e (2), b (3)). On standing, in solution, this complex undergoes decarbonylation to give the cluster [Os7(CO)19{Au2(dppx)}] (x=m (4), e (5), b (6)). The complexes have been characterised spectroscopically, and an X-ray structure determination of the dppm derivative shows that it contains a metal core based on an Os7 edge-bridged bicapped tetrahedron with the two
3-Au atoms capping adjacent triangular Os3 faces of the central tetrahedron. In an analogous reaction, the carbido anion [Os7(H)C(CO)19]– affords the neutral cluster [Os7C(CO)19{Au2(dppm)}] (7) when treated with [Au2(dppm)]2+ in the presence of base. 相似文献
18.
Norman S. Allen Alfonso Chirinos-Padron John H. Appleyard 《Polymer Degradation and Stability》1984,6(3):149-176
The interactions of three metal chelates (nickel (II) 2,2′-thiobis (4-tertoctyl-phenolato), n-butylamine (Cyasorb UV 1084) and the nickel and calcium derivatives of bis(ethyl-3,5-di-tert-butyl-4-hydroxybenzyl) phosphonate (Irgastab 2002 and Irganox 1425)) with other commercial additives, in the stabilisation of polypropylene film, are examined using normal and second-order derivative ultraviolet and infra-red spectroscopic techniques. It is shown that the observed behaviour is dependent on the particular additive, the processing history of the polymer and the metal chelate concerned, and is therefore highly complex. All three chelates show antagonism with a hindered piperidine, bis(2,2,6,6-tetramethyl-4-piperidinyl) sebacate (Tinuvin 770), in unprocessed polymer, whereas one of the chelates behaves synergistically with this additive in processed samples. The chelates also show antagonism with a primary antioxidant, tris((3-(3′,5′-di-tert-butyl-4-hydroxybenzyl)-2′'-aceto-ethyl)) isocyanurate (Goodrite 3125), whereas, with a secondary antioxidant, distearyl pent-aerithrityl diphosphite (Weston 618), their behaviour is synergistic in both unprocessed and processed polymer. Two of the chelates show synergism with 2-hydroxy-4-n-octoxybenzophenone (Cyasorb UV 531), the remaining chelate showing antagonism. Mixtures containing a three-additive system show a more complex behaviour. The results are explained in terms of hydroperoxide decomposition, inhibition, stabiliser dispersion, ultraviolet stability and additive compatibility. 相似文献
19.
Grez P Celedón C Molinari A Oliva A Orellana M Schrebler R del Río R Córdova R 《The journal of physical chemistry. B》2005,109(48):22920-22927
The interaction of the ethyl xanthate (EX) anion with a copper electrode in a borate buffer solution, pH 9.2, has been investigated by cyclic voltammetry (CV), electrochemical quartz crystal microbalance (EQCM), electrochemical impedance spectroscopy (EIS), and measurements of contact angle (CA) under controlled potential. The results obtained allow establishing that, in the potential range from -0.80 and -0.60 V, two parallel reactions were characterized. These reactions were the ethyl xanthate electroadsorption and the hydrogen evolution reaction (HER). This last reaction has not been described by previous authors. Besides, the EIS measurements show that the mechanism of the HER on copper electrodes is not affected by the presence of a ethyl xanthate species. The EQCM study shows that in the electrodesorption process the departure of each ethyl xanthate species from the copper electrode is accompanied with the simultaneous entry of four to five water molecules. This fact is in accordance with the number of copper atoms involved in the adsorption of one ethyl xanthate species. 相似文献
20.
Guimarães KL Castro RH Gouvêa D 《Langmuir : the ACS journal of surfaces and colloids》2005,21(25):11645-11650
The standard methods for obtaining adsorption isotherms on colloidal suspensions are usually very time consuming and involve a large number of steps and assumptions that increase the experimental errors. In this work, an alternative method is proposed to evaluate the adsorption behavior of electrosteric-stabilized systems based on electrokinetic sonic amplitude signal measurements. The new method, entitled "zeta-sorption", is noticeably less time-consuming when compared to conventional procedures but showed great precision and reliability confirmed by comparison with data obtained from conventional routes on alumina-polyacrylate and alumina-citric acid aqueous suspensions. The experimental conditions that restrict the applicability of the new method were identified and justified by discussing the possible ion exchanges. 相似文献