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In this paper, we evaluated the use of a silylation reagent N-methyl-N-(tert-butyldimethylsilyl)trifluoroacetamide in the microwave-assisted derivatization method to replace a traditional prolonged heating method for the determination of 12 amino acids. Several parameters, including the kind of extraction solvent, extraction time, microwave power and microwave time, were optimized. The experiment showed that the optimal derivatization time was 3 min with a microwave power of 240 W. The calibration curves were linear with the correlation coefficients ranging from 0.995 to 1.000 in the concentration levels between 0.1-20 [mu]g/mL and the relative standard deviations were between 4.4 and 18%. The limits of detection were 0.1-2.4 [mu]g/mL and the recoveries of those compounds were 62-115%. A comparison of this method to other methods has demonstrated that the proposed method is a rapid and reliable sample-treatment procedure for amino acids determination in real tobacco samples., Author(s): Jing Wang [sup.1], Shao Min Liu [sup.2], Jun Long [sup.1], De An Lei [sup.1], Feng Gao [sup.1] Author Affiliations: (1) Research and Development Center, China Tobacco Sichuan Industrial Corporation, [...]

The photocatalytic conversion of CO2 into widely adjustable syngas (CO/H2 mixture) has been considered as an extraordinarily promising but challenging strategy to realize high value-added utilization of CO2 to alleviate worldwide environmental problems and energy crisis. To achieve this goal, we report a newly designed crystalline covalent organic framework (COF-TVBT-Bpy) that embedded a series of metal active sites to efficiently convert CO2 and H2O into syngas under visible-light illumination. COF-TVBT-Bpy not only provides a coordination environment for the metal center, but also enhances electron delocalization by the extended conjugated moiety, thus facilitating electron transfer. The optimized Co@COF-TVBT-Bpy achieves the highest photocatalytic CO2-to-syngas conversion efficiency in pure CO2 (up to 2291.1 μmol g−1 h−1, CO/H2 ≈ 1 : 1). The intrinsic reason for a CO/H2 ratio of 1 : 1, electron transfer pathway, and syngas generation mechanism over Co@COF-TVBT-Bpy are explored by the combination of in situ measurements and theoretical calculations. The experimental results confirm that the ratio of CO/H2 can be widely modulated by adjusting the metal active sites and photoreaction conditions. This work proves the immense potential of utilizing COFs as platforms to anchor metal active sites for syngas formation and provides a facile method to regulate the ratio of syngas in a wide range. [ABSTRACT FROM AUTHOR]

Significant progress has recently been made in the synthesis of Fe3O4@C nanospheres with uniform, monodisperse and tunable carbon shells. Fe3O4@C nanospheres were obtained by directly carbonizing Fe3O4@polymer which was synthesized by a versatile and economical Stöber method with resorcinol and formaldehyde as precursors. The synthesis conditions in the formation of Fe3O4@polymer were systematically investigated. It was found that the yield of the Fe3O4@polymer is highly influenced by the concentration of ammonium hydroxide, and the monodispersity is mainly affected by the concentration of ammonium hydroxide and the citrate group sites outside the surfaces of the Fe3O4 nanospheres. Interestingly, carbonization of Fe3O4@polymer at high temperature makes the grain sizes of Fe3O4 in Fe3O4@C samples larger than those in the Fe3O4 sample, which makes the saturation magnetization value for the Fe3O4@C samples higher than those of common obtained materials. The adsorption performance of Fe3O4@C for anthracene was tested both in water and in cyclohexane solution; it shows fast adsorption rates (about 1 h to reach equilibrium in water and 3 h in cyclohexane solution) and high adsorption capacities (31.5 mg g−1 in water and 2 mg g−1 in cyclohexane solution), which are ascribed to its high uniformity and monodispersity. These make Fe3O4@C an ideal adsorption and enrichment material, especially for polycyclic aromatic hydrocarbons in water and in organic solvents. [ABSTRACT FROM AUTHOR]

To extract, preconcentrate and determine the trace level of environmental contaminants, a novel mixed hemimicelles solid-phase extraction (MHSPE) method based on mesoporous silica-coated magnetic nanoparticles (Fe3O4/meso-SiO2 NPs) as adsorbent was developed for extraction of phthalate esters from water samples. The Fe3O4/meso-SiO2 NPs were synthesized by using a combination of hydrothermal method and sol-gel method. The obtained Fe3O4/meso-SiO2 NPs possessed a large surface area (570 m2/g), superparamagnetism, and uniform mesopores (2.8 nm). MHSPE parameters, such as the amount of surfactant, pH of sample, shaking and separation time, eluent and breakthrough volume that may influence the extraction of analytes greatly, were further investigated. Under the optimized conditions, the extraction was completed in 20 min and a concentration factor of 500 was achieved by extracting 250 mL water sample. Detection limits obtained of butyl-benzyl phthalate (BBP), di-n-butyl phthalate (DnBP), di-(2-ethylhexyl) phthalate (DEHP) and di-n-cotyl phthalate (DnOP) were 12, 21, 12, and 32 ng/L, respectively. The proposed method exhibited high extraction efficiency and relatively short time for extracting the target compounds. [ABSTRACT FROM AUTHOR]

Although phytosterols in tobacco leaves have specific effects on tobacco quality, there is little research on the distribution of free and conjugated phytosterols in various tobacco leaves. In this paper, we explored the content and composition of phytosterols in representative cured tobacco leaves by gas chromatography of TMS-ether derivatives. We found that phytosterol contents in tobacco leaves ranged from 1.0 to 2.5 mg/g of dried leaf tissue, depending on different types of tobacco leaves. The majority of phytosterols (75-85%) were conjugated as ester and glycosides, with only about 15-25% existing in the free form. Furthermore, the genetic variability gives rise to the significant differences among different tobacco types with phytosterol levels: the contents of phytosterols in tobacco leaves decreased in the order of flue-cured tobacco, Oriental tobacco, Burley tobacco, cigar tobacco, and Maryland tobacco. At the same time, the tobacco curing process leads to a difference in phytosterol existing-form distribution in some variation laws.

The interaction of BSA and NIC was investigated by absorption spectra, fluorescence spectroscopy and synchronous fluorescence spectroscopy. In the system of sodium phosphate dibasic-citric acid of 0.1 mol(-1) x L(-1), fluorescence titration showed that the fluorescence intensity of BSA at 342 nm was quenched when NIC was added, NIC was capable of binding with BSA to form a 1:1 complex and the quenching mechanism of BSA affected by NIC was shown to be a static quenching procedure by calculating the binding number n and binding constant K. NIC decreased the intensity of the characteristic absorption peak of BSA, showing that the binding of NIC to BSA had strong impact on protein conformation with the decrease in a-helical content of the protein. Synchronous fluorescence indicated that the binding of NIC to BSA is near tryptophan subunit.

Cerium incorporated MCM-48 molecular sieves have been hydrothermally synthesized using a mixed template and pH adjusting route. The samples were characterized by various physicochemical methods, including X-ray diffraction, diffuse reflectance UV-Vis spectroscopy, FTIR spectroscopy, XRF spectroscopy, and nitrogen adsorption. These results reveal that cerium is incorporated in MCM-48 and it is in the form of well-dispersed tetra-coodinated cerium ion. The proper concentration of cerium and adjusting pH can keep Ce-MCM-48 with higher specific surface area , larger unit-cell parameter, narrower pore-size distribution, and thicker pore wall than those of MCM-48. These deduce higher activity, and better selectivity, thermal stability and hydrothermal stability than those of MCM-48. The concentration of Ce incorporated in MCM-48 affects the vibration of the framewoke Si of molecular sieves.

The synchronous fluorescence, first-order and second-order-derivative synchronous fluorescence spectra of BaP in cigarette mainstream smoke were studied. It was indicated that the second-order-derivative synchronous fluorescence spectrum could decrease the disturbances of BaP homologous compounds and background of sample. Hereby the present paper introduces a new method to determine BaP in cigarette mainstream smoke by solid-phase-extraction second-order-derivative synchronous fluorescence. The detection limit is 0.2 ng x mL(-1), the average recoveries of BaP are 80.2%-86.2%, and the RSD is 2.64%-3.02%.