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1.
The preparation and characterization of biodegradable films based on starch-PVA-nanoclay by solvent casting are reported in this study. The films were prepared with a relation of 3:2 of starch:PVA and nanoclay (0.5, 1.0, and 1.5% w/v), and glycerol as plasticizer. The nanoclays before being incorporated in the filmogenic solution of starch-PVA were dispersed in two ways: by magnetic stirring and by sonication. The SEM results suggest that the sonication of nanoclay is necessary to reach a good dispersion along the polymeric matrix. FTIR results of films with 1.0 and 1.5% w/v of sonicated nanoclay suggest a strong interaction of hydrogen bond with the polymeric matrix of starch-PVA. However, the properties of WVP, tensile strength, percentage of elongation at break, and Young’s modulus improved to the film with sonicated nanoclay at 0.5% w/v, while in films with 1.0 and 1.5% w/w these properties were even worse than in film without nanoclay. Nanoclay concentrations higher than 1.0 w/v saturate the polymer matrix, affecting the physicochemical properties. Accordingly, the successful incorporation of nanoclays at 0.5% w/v into the matrix starch-PVA suggests that this film is a good candidate for use as biodegradable packaging.  相似文献   
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A colorimetric method based on silver nanoparticles was developed for the determination of melamine in milk. Silver nanoparticles were synthesized without any stabilizer, using sodium borohydride as the reducing agent. Optimization of the variables for the formation of the nanoparticles was performed by factorial design, resulting in stable colloidal silver nanoparticles with a mean diameter of 14.0?±?2.7?nm. Spectrophotometric measurements performed at 475?nm showed a linear range from 0.033 to 1.50?mg?L?1 of melamine with limits of detection and quantification of 0.009 and 0.031?mg?L?1, respectively. The method provided highly sensitive determination of melamine in milk.  相似文献   
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The release of alkaloids from root culturesDatura stramonium andCatharanthus roseus and thiophenes from root cultures ofTagetes patula was found to increase when the pH of the culture media (ranging from 4.8 to 7.0) was reduced to 3.5. The extent of the effect was different in each type of culture. Increases ranged from 4- to 20-fold, which in some cases accounted for 75% of the total secondary metabolite pool produced per flask. When the release of individual metabolites was measured, even larger increases, were observed (nearly 400-fold for ajmalicine). Increased release of alkaloids fromC. roseus roots were also observed in cultures growing in a 14-L fermentor, when the medium pH was reduced. Reduction of the pH of the media did not affect growth of the root cultures in subsequent subcultures. The importance of this treatment as a stategy to improve the recovery of secondary metabolites from producing cultures is discussed.  相似文献   
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Exposure to 4-aminobiphenyl (4-ABP), an environmental and tobacco smoke carcinogen that targets the bladder urothelium, leads to DNA adduct formation and cancer development [1]. Two major analytical challenges in DNA adduct analysis of human samples have been limited sample availability and the need to reach detection limits approaching the part-per-billion threshold. By operating at nano-flow rates and incorporating a capillary analytical column in addition to an online sample enrichment step, we have developed a sensitive and quantitative HPLC–MS/MS method appropriate for the analysis of such samples. This assay for the deoxyguanosine adduct of 4-ABP (dG-C8-4-ABP) gave mass detection limits of 20 amol in 1.25 μg of DNA (5 adducts in 109 nucleosides) with a linear range of 70 amol to 70 fmol. 4-ABP-exposed human bladder cells and rat bladder tissue were analyzed in triplicate, and higher dose concentrations led to increased numbers of detected adducts. It was subsequently established that sample requirements could be further reduced to 1 μg digestions and the equivalent of 250 ng DNA per injection for the detection of low levels of dG-C8-4-ABP in a matrix of exfoliated human urothelial cell DNA. This method is appropriate for the characterization and quantification of DNA adducts in human samples and can lead to a greater understanding of their role in carcinogenesis and also facilitate evaluation of chemopreventive agents.  相似文献   
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The cyanide oxidation on vitreous carbon (VC), stainless steel 304 (SS 304) and titanium (Ti) was investigated through a voltammetric study of cyanide solutions also containing copper ions. Results showed that cyanide oxidation occurs by means of a catalytic mechanism involving adsorbed species as CN, Cu(CN)43– or Cu(CN)42– depending on the electrode material. It was observed that on VC, the adsorption of Cu(CN)43– controlled the oxidation rate. Instead, for SS 304 and Ti, the adsorption of CN controlled the global process. However, in all cases, the adsorption of Cu(CN)43– on the electrode surface was required for the catalytic oxidation of CN. Voltammetric experiments for solutions containing cyanide oxidation products, such as cyanogen (CN)2 and cyanate (CNO), confirmed that the adsorbed species mentioned above controlled the catalytic oxidation of CN depending on the electrode material. A voltammetric identification of the oxidation products showed that cyanogen, (CN)2 tended to adosorb on VC, while the formation of cyanate, CNO predominated on SS 304.  相似文献   
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The essential oil from leaves of Croton gossypiifolius Vahl. (Euphorbiaceae) was obtained by hydrodistillation, and analyzed by GC/FID and GC/MS. The constituents were identified by their mass spectra and Kovats' indices. Fifty-one compounds accounting for 92% of the oil were detected, and 47 of them were identified. The oil was dominated by oxygenated sesquiterpenes with the major presence of alpha-cedrene oxide (18.6%), spathulenol (16.3%), valencene (5.8%), geranyl-pentanoate (5.3%), alpha-cadinol (4.0%), germacrene D (3.5%) and longifolene (3.3%).  相似文献   
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Nanoengineering biosensors have become more precise and sophisticated, raising the demand for highly sensitive architectures to monitor target analytes at extremely low concentrations often required, for example, for biomedical applications. We review recent advances in functional nanomaterials, mainly based on novel organic-inorganic hybrids with enhanced electro-physicochemical properties toward fulfilling this need. In this context, this review classifies some recently engineered organic-inorganic metallic-, silicon-, carbonaceous-, and polymeric-nanomaterials and describes their structural properties and features when incorporated into biosensing systems. It further shows the latest advances in ultrasensitive electrochemical biosensors engineered from such innovative nanomaterials highlighting their advantages concerning the concomitant constituents acting alone, fulfilling the gap from other reviews in the literature. Finally, it mentioned the limitations and opportunities of hybrid nanomaterials from the point of view of current nanotechnology and future considerations for advancing their use in enhanced electrochemical platforms.  相似文献   
10.
There is a great demand for simple, fast and accurate methods for quantification of volatile organic contaminants in soil samples. Solid-phase microextraction (SPME) has a huge potential for this purpose, but its application is limited by insufficient accuracy caused by a matrix effect. The aim of this research was to develop the method for BTEX quantification in soil using combined standard addition (SA) and internal standard (IS) calibration. Deuterated benzene (benzene-d6) was used as the internal standard for all analytes. The optimized method includes spiking replicate samples with different concentrations of BTEX standards and the same concentration of benzene-d6, equilibration of soil samples at 40 °C during 2 h, and SPME–GC–MS analysis. Precision and accuracy of IS and SA methods were compared on different soil matrices. Combined SA + IS method provided more precise calibration plots compared to the conventional SA calibration. The SA + IS calibration provided more precise and accurate results compared with a reference method based on solvent extraction followed by GC–MS when applied to BTEX quantification in real soil samples (spiked with diesel fuel and aged). Recoveries of BTEX from soil samples spiked with known concentrations of analytes using the developed method were in the range of 73–130% with RSD values less than 15% for all BTEX. The proposed simultaneous standard addition and internal standard approach can be advantageous and adopted for improved quantification of other toxic VOCs in soil.  相似文献   
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