An efficient analytical method is presented involving effective sample clean-up with solid-phase extraction and HPLC-UV analysis for the simultaneous determination of carbendazim, thiabendazole, and o-phenylphenol residues in lemons. Sample preparation involves extraction with acetonitrile acidified with trifluoroacetic acid and an ethyl acetate/petroleum ether mixture. Purification of the crude extract was carried out with liquid–liquid partitioning after addition of an aqueous ammonia solution. Final clean-up was performed on polymeric reversed-phase cartridges pretreated with sodium dodecyl sulfate. Chromatographic analysis was performed on a reversed-phase HPLC column isocratically eluted with an acetonitrile/water/ammonia mixture and UV detection at 254 nm. The chromatographic method is repeatable, reproducible, and sensitive. Fungicide recoveries from lemon samples fortified at levels of 5 and 1 mg kg–1 were 81–85% for carbendazim, 96–98% for thiabendazole, and 81–106% for o-phenylphenol with coefficients of variation of 2.5–7.4%. Detection limits for carbendazim, thiabendazole, and o-phenylphenol in lemons were 0.21, 0.27, and 0.51 mg kg–1, respectively. 相似文献
Ketoreductases were utilized for the stereoselective synthesis of δ-hydroxy-β-keto esters, β-hydroxy-δ-keto esters, and β,δ-dihydroxy esters. Seven out of eight possible stereoisomers were obtained from the enzymatic reduction of the corresponding β,δ-diketo ester in high enantio- and diastereomeric excess. 相似文献
Statistical Inference for Stochastic Processes - The problem of linear interpolation in the context of a multivariate time series having multiple (possibly non-consecutive) missing values is... 相似文献
The traditional triadic 'Teaching System' (the teacher, the student and mathematics) and the new quaternary version (the teacher, the student, mathematics and new technologies), are studied according to Systems Theory. Systems Theory is described and the model of the traditional 'Teaching System' and that of the new system are analysed with the aid of this theory; that is the structure of each system (elements, interactions) and its function are described. Finally, comments are made about the application of the new system on didactic, on the one hand, and the philosophical background of the incorporation of the fourth element (new technologies) in the traditional system, on the other. 相似文献
Let Y and Z be two fixed topological spaces and C(Y, Z) the set of all continuous maps from Y into Z. We construct and study topologies on C(Y, Z) that we call Fn(τn)-family-open topologies. Furthermore, we find necessary and su?cientconditions such that these topologies to be splitting and jointly continuous. Finally, we present questions concerning a further study on this area. 相似文献
The model and methodology for estimating diffusion‐controlled rate coefficients for the methyl methacrylate (MMA) polymerization system is extended to the vinyl acetate (VAc) case. Comparison of the kinetic behavior and termination rate coefficients (kt) of both monomers suggests that at low conversions the termination reaction is controlled by the chemical step, whereas at moderate and high conversions it is controlled by the diffusive step which in turn is determined by the segmental diffusion of the long radicals and not by the center of mass diffusion of short radicals. It is found that, for most of the conversion range, diffusion coefficient for VAc is lower than the one for MMA notwithstanding that ktVAc > ktMMA. An explanation of this apparent inconsistency on the base of the model results and in terms of segmental mobility is proposed.
A cheap, mild and environmentally friendly oxidation of tertiary amines and azines to the corresponding N‐oxides is reported by using polyfluoroalkyl ketones as efficient organocatalysts. 2,2,2‐Trifluoroacetophenone was identified as the optimum catalyst for the oxidation of aliphatic tertiary amines and azines. This oxidation is chemoselective and proceeds in high‐to‐quantitative yields utilizing 10 mol % of the catalyst and H2O2 as the oxidant. 相似文献
A hyperbranched aliphatic polyester has been functionalized with PEG chains to afford a novel water-soluble BH40-PEG polymer which exhibits unimolecular micellar properties, and is therefore appropriate for application as a drug-delivery system. The solubility of the anticancer drug paclitaxel was enhanced by a factor of 35, 110, 230, and 355 in aqueous solutions of BH40-PEG of 10, 30, 60, and 90 mg x mL(-1), respectively. More than 50% of the drug is released at a steady rate and release is almost complete within 10 h. The toxicity of BH40-PEG was assessed in vitro with A549 human lung carcinoma cells and found to be nontoxic for 3 h incubation up to a 1.75 mg x mL(-1) concentration while LD50 was 3.5 mg x mL(-1). Finally, it was efficiently internalized in cells, primarily in the absence of foetal bovine serum, while confocal microscopy revealed the preferential localization of the compound in cell nuclei. [Figure: see text]. 相似文献
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