Determination of sodium, potassium, calcium, magnesium, zinc, and iron in emulsified egg samples by flame atomic absorption spectrometry

In this study, oil-in-water formulations were optimized to determine sodium, potassium, calcium, magnesium, zinc, and iron in emulsified egg samples by flame atomic absorption spectrometry (FAAS). This method is simpler and requires fewer reagents when compared with other sample pre-treatment procedures and allows the calibration to be carried out using aqueous standards. Different oily phases such as corn oil, decyl oleate and octyl stearate were tested, as well as Tween 80, Triton X-100 and Triton 114 were analyzed as surfactants. The optimum type and proportion of formulations were determined and their use depended on the element studied. The emulsion preparation was performed by a conventional method that involves mixing both phases at 60 °C by magnetic stirring and phase inversion to change the water-to-oil ratio by increasing the volume of the surfactant-water external phase and correspondingly decreasing the volume of internal phase. The accuracy of the method was further confirmed by determining the metals in a whole egg powder CRM and recoveries ranged from 97.5% for Mg to 102.2% for Na, with relative standard deviations lower than 2.3%. The precision of the procedures was determined through repeatability (intra-day precision) and intermediate precision (inter-day). The repeatability presented RSD values lower than 4.2%. The intermediate precision was evaluated using the RSD and F-test. The RSD values to intermediate precision was lower than 5.3% and the computed F-values were lower than tabulated F-values, indicating no significant difference between the results obtained on different days. The proposed method including, sample emulsification for subsequent metal determination for FAAS, has proved to be sensitive, reproducible, simple and economical.     

Videomicroscopy calibration of optical tweezers by position autocorrelation function analysis

We present a simple method to calibrate optical tweezers by using only videomicroscopy to measure the position autocorrelation function of the trapped bead in the potential well of the tweezers. To accomplish this task, we use a high-speed camera with ??500 fps (frames per second), which provides a precise measurement of the relaxation time of the bead Brownian fluctuations. We also study the variation of the trap stiffness as a function of some parameters of interest such as the laser power and the distance from the bead center to the microscope coverslip, showing that the presented method returns precise results.     

Combining multinuclear high-resolution solid-state MAS NMR and computational methods for resonance assignment of glutathione tripeptide

We present a complete set of experimental approaches for the NMR assignment of powdered tripeptide glutathione at natural isotopic abundance, based on J-coupling and dipolar NMR techniques combined with (1)H CRAMPS decoupling. To fully assign the spectra, two-dimensional (2D) high-resolution methods, such as (1)H-(13)C INEPT-HSQC/PRESTO heteronuclear correlations (HETCOR), (1)H-(1)H double-quantum (DQ), and (1)H-(14)N D-HMQC correlation experiments, have been used. To support the interpretation of the experimental data, periodic density functional theory calculations together with the GIPAW approach have been used to calculate the (1)H and (13)C chemical shifts. It is found that the shifts calculated with two popular plane wave codes (CASTEP and Quantum ESPRESSO) are in excellent agreement with the experimental results.     

CO2 adsorption on calcium oxide: An atomic-scale simulation study

We present a detailed study of CO₂ adsorption on CaO, by means of atomic-scale simulations relying on Density Functional Theory. Combining ab initio thermodynamics of the CO₂ gas phase and a thorough analysis of its interaction with the oxide, we build an orientation-sensitive adsorption model, which demonstrates that low coverage by the gas is expected in a wide range of working conditions, including the domain of stability of CaCO₃ calcite. Investigation of the interactions between the adsorbed molecules reinforces this conclusion. Our work thus provides a strong hint that calcite nucleation should occur by a localised mechanism, discarding the possibility of collective surface transformation.     

Schwarzschild generalized black hole horizon and the embedding space

The European Physical Journal C - By performing a Taylor expansion along the extra dimension of a metric describing a black hole on a brane, we explore the influence of the embedding space on the...     

On Iterated Maps of the Interval with Holes

A kneading theory is generalized to maps of the interval with several discontinuity points and holes. Alternative methods to evaluate topological entropy are introduced and related. Also we study the parametrization of families of maps with holes and the monotonicity properties of the topological entropy.     

The use of the fractal model to complex resistivity in the interpretation of induced polarization data

Several researchers demonstrated that spectral parameters in induced polarization can be applied to discriminate different IP sources. In this paper it was applied an inversion procedure using the Gauss–Newton method to recover the spectral parameters of fractal model to complex resistivity. The finite element method was applied to carry out the forward modeling. The procedure was applied in synthetic data and simulations were carried out in five different frequencies. The inversion of the data were carried out in each frequency, further the inversion was applied also to each cell of the finite element mesh to recover the fractal parameter in order to analyze the possibility of using the fractal model parameters in the interpretation of the induced polarization response to this geological geometry. The results showed that the anomalies are well detected by the image of the fractal model parameters.     

A biosorption isotherm model for the removal of reactive azo dyes by inactivated mycelia of Cunninghamella elegans UCP542

The biosorption of three reactive azo dyes (red, black and orange II) found in textile effluents by inactive mycelium of Cunninghamella elegans has been investigated. It was found that after 120 hours of contact the adsorption led to 70%, 85%, 93% and 88% removal of reactive orange II, reactive black, reactive red and a mixture of them, respectively. The mycelium surface was found to be selective towards the azo dyes in the following order: reactive red > reactive black > orange II. Dye removal from a mixture solution resulted in 48.4 mg/g retention by mycelium and indicated a competition amongst the dyes for the cellular surface. A Freundlich adsorption isotherm model exhibited a better fit, thus suggesting the presence of heterogeneous binding sites. Electrondense deposits observed on the mycelium ultrastructure suggest that the dyes are mainly retained under the cellular surface of the inactive biomass of C. elegans.     

Characterization by 27Al NMR, X-ray absorption spectroscopy, and density functional theory techniques of the species responsible for benzene hydrogenation in Y zeolite-supported carburized molybdenum catalysts

Carburized molybdenum catalysts supported on a dealuminated NaH-Y zeolite were prepared by carburization under a 20% methane in hydrogen flow of two precursors obtained by adsorption of molybdenum hexacarbonyl, one containing 5 wt % and the other 10 wt % Mo, and a third one was prepared by impregnation with aqueous ammonium heptamolybdate, containing 5 wt % Mo. The three catalysts displayed very distinct behaviors in the benzene hydrogenation reaction at atmospheric pressure and 363 K. By using XANES spectroscopy at the molybdenum L edge, EXAFS and XANES spectroscopy at the molybdenum K edge, and 27Al solid-state NMR spectroscopy, it was shown that different carburized molybdenum species exist in each sample. In the catalyst containing 10 wt % Mo, formation of molybdenum carbide nanoparticles was observed, with an estimated diameter of 1.8 nm. In the catalyst containing 5 wt % Mo and prepared by carburization of adsorbed molybdenum hexacarbonyl, formation of molybdenum oxycarbide dimers is proposed. In the latter case, density functional theory calculations have led to a dimer structure which is compatible with EXAFS results. In the catalyst prepared by impregnation with ammonium heptamolybdate solution followed by carburization, the molybdenum seems to interact with extraframework alumina to produce highly disordered mixed molybdenum-aluminum oxycarbides.