Effect of support and pre-treatment conditions on Pt-Sn catalysts: application to nitrate reduction in water

The effect of the support (activated carbon or titanium dioxide) on the catalytic activity and selectivity to nitrogen of Pt-Sn catalysts in nitrate reduction was studied. The effects of the preparation conditions and the Pt:Sn atomic ratio were also evaluated. It was observed that the support plays an important role in nitrate reduction and that different preparation conditions lead to different catalytic activities and selectivities. Generally, the catalysts supported on activated carbon were less active but more selective to nitrogen than those supported on titanium dioxide. The monometallic Pt catalyst is active for nitrate reduction only when supported on titanium dioxide, which is explained by the involvement of the support in the reaction mechanism. The catalysts were characterized by different techniques, and significant changes on metal chemical states were observed for the different preparation conditions used. Only metallic Pt and oxidized Sn were observed at low calcination and reduction temperatures, but some metallic Sn was also present when high temperatures were used, being also possible the formation of Pt-Sn alloys.     

Na<Subscript>x−y</Subscript>H<Subscript>y</Subscript>Ti<Subscript>2−x</Subscript>Fe<Subscript>x</Subscript>O<Subscript>4</Subscript>·nH<Subscript>2</Subscript>O nanosheets with lepidocrocite-like layered structure synthesized by hydrothermal treatment of ilmenite sand

Na_x−yH_yTi_2−xFe_xO₄·nH₂O nanosheets with lepidocrocite-like layered structure were produced through alkaline hydrothermal treatment at very low temperatures (130°C) from ilmenite sand. The crystal structure, morphology and optical properties were investigated by X-Ray diffraction, transmission electron microscopy, selected area electron diffraction, energy dispersive spectroscopy and UV-Vis spectroscopy. The product shows leaf-like nanosheet morphology with thickness <30 nm and lengths <1 μm. Three lepidocrocite-like titanates (Imm2 space group) with similar a and c lattice parameters but different interlayer distances (b/2) were identified. This appears to be the first preparation of lepidocrocite-like layered nanosheets by a simple, energy efficient (low temperature) and low cost (starting from mineral sand) procedure.     

A Fourier–Mukai transform for real torus bundles

We construct a Fourier–Mukai transform for smooth complex vector bundles E over a torus bundle π:M→B, the vector bundles being endowed with various structures of increasing complexity. At a minimum, we consider vector bundles E with a flat partial unitary connection, that is families or deformations of flat vector bundles (or unitary local systems) on the torus T. This leads to a correspondence between such objects on M and relative skyscraper sheaves supported on a spectral covering , where is the flat dual fiber bundle. Additional structures on (E,) (flatness, anti-self-duality) will be reflected by corresponding data on the transform . Several variations of this construction will be presented, emphasizing the aspects of foliation theory which enter into this picture.     

Comparison of Different Sorbents in the QuEChERS Method for the Determination of Pesticide Residues in Strawberries by LC–MS/MS

A comparison of sample preparation based on the quick, easy, cheap, effective, rugged and safe (QuEChERS) method for analysis of pesticide residues in strawberries by LC–MS/MS was made using different sorbents in the clean-up by dispersive solid-phase extraction (d-SPE). Some sorbents were laboratory-made, prepared by depositing poly(methyloctadecylsiloxane) (PMODS), poly(methyloctylsiloxane) (PMOS), aminopropyl-terminated poly(dimethylsiloxane) (APPS) and copolymer of (52–48 %)dimethyl-(48–52 %)methylphenyl-siloxane (DMMPS) onto silica supports. The commercial sorbent primary–secondary amine (PSA) and mixtures of two sorbents, primary–secondary amine and poly(methyloctadecylsiloxane), were also used in the experiments. The performances of the sorbents were evaluated by parameters such as color of the final extract, gravimetric measurement, recovery and matrix effect at the fortification level of 100 ng g^?1 of the pesticide mixture in strawberries. The recoveries were in the range 70–120 %, and the RSD values were lower than 20 % for most of the pesticides using the modified QuEChERS method with different sorbents in the clean-up step. The strawberry extracts were cleaned more efficiently with the use of primary–secondary amine sorbent, which has the function of removing sugars, organic acids and especially pigments. The sample preparation method was efficient, and LC–MS/MS determination was optimal because of high selectivity and good detectivity for the multiresidue analyses.     

Combined column–mobile phase mixture statistical design optimization of high-performance liquid chromatographic analysis of multicomponent systems

A statistical approach for the simultaneous optimization of the mobile and stationary phases used in reversed-phase liquid chromatography is presented. Mixture designs using aqueous mixtures of acetonitrile (ACN), methanol (MeOH) and tetrahydrofuran (THF) organic modifiers were performed simultaneously with column type optimization, according to a split-plot design, to achieve the best separation of compounds in two sample sets: one containing 10 neutral compounds with similar retention factors and another containing 11 pesticides. Combined models were obtained by multiplying a linear model for column type, C8 or C18, by quadratic or special cubic mixture models. Instead of using an objective response function, combined models were built for elementary chromatographic criteria (retention factors, resolution and relative retention) of each solute or pair of solutes and, after their validation, the global separation was accomplished by means of Derringer's desirability functions. For neutral compounds a 37:12:8:43 (v/v/v/v) percentage mixture of ACN:MeOH:THF:H₂O with the C18 column and for pesticides a 15:15:70 (v/v/v) ACN:THF:H₂O mixture with the C8 column provide excellent resolution of all peaks.     

Use of NMR Relaxometry to identify frankfurters of different meat sources

ABSTRACT

Frankfurters are categorised as ready to eat meat products and are prepared by using different meat sources including beef, chicken, turkey or pork or mixtures of them. Due to cost and feasibility, it is very common to adulterate beef-, chicken- and turkey-based frankfurters with pork meat. Since pork is not consumed by some part of the population due to religion, it is important to identify pork frankfurters based on easy quality control methods. In this study, NMR Relaxometry was used to differentiate four different frankfurter types based on their relaxation times. Relaxation measurements were conducted on three permanent field benchtop NMR spectrometers (13.52/20.34/22.35?MHz) and also using an FFC Relaxometer at a frequency range of 40?kHz–8.86?MHz. Physical properties of frankfurters such as moisture and solid fat contents, water activity (a_w) and hardness values were also measured. Results showed that among the permanent field systems, 22.34?MHz was the best to differentiate frankfurters based on both T₁ and T₂ relaxation times. FFC experiments also showed that the dependence of T₁ with respect to frequency follows a well fitted power law behaviour throughout the whole frequency range (R²?>?0.97) and the highest difference on T₁ was observed at the lowest frequency of 40?kHz. Thus the results of the study showed that NMR Relaxometry has the potential to discriminate frankfurters of different meat origin. Further studies are needed to detect the authenticity of the type of mixture in frankfurters.     

Method for analyzing second-order phase transitions: application to the ferromagnetic transition of a polaronic system

A new method for analyzing second-order phase transitions is presented and applied to the polaronic system La(0.7)Ca(0.3)MnO3. It utilizes heat capacity and thermal expansion data simultaneously to correctly predict the critical temperature's pressure dependence. Analysis of the critical phenomena reveals second-order behavior and an unusually large heat capacity exponent.     

Poly(methyloctadecylsiloxane) immobilized on silica by gamma radiation for use in solid-phase extraction

The suitability of using metal-loaded sorbents for solid-phase extraction to enrich organic sulfur compounds from water samples was studied. To test the retention behavior of a number of sulfides, thiols and methylthiophosphates, a cation-exchanger was loaded with various metal ions. The elution behavior of sulfur compounds was investigated with different solvents. A combination of Pb2+-modified cation-exchanger as sorbent and CS2 (1%, v/v) in toluene proved to be the most suitable approach for the given problem. Using GC with a pulsed flame photometric detector yielded detection limits of between 0.6 and 2.9 microg/l. The results showed good reproducibility with relative standard deviations of 2-11%.