Simultaneous Titration of Ternary Mixtures of Pb(II), Cd(II) and Cu(II) with Potentiometric Electronic Tongue Detection

An automatic titration method is reported to resolve ternary mixtures of transition metals (Pb²⁺, Cd²⁺ and Cu²⁺) employing electronic tongue detection and a reduced number of pre‐defined additions of EDTA titrant. Sensors used were PVC membrane selective electrodes with generic response to heavy‐metals, plus an artificial neural network response model. Detection limits obtained were ca. 1 mg L^?1 for the three target ions and reproducibilities 3.0 % for Pb²⁺, 4.1 % for Cd²⁺ and 5.2 % for Cu²⁺. The system was applied to contaminated soil samples and high accuracy was obtained for the determination of Pb²⁺. In the determination Cd²⁺ and Cu²⁺, sample matrix showed a significant effect.     

Simulating periodic trends in the structure and catalytic activity of coinage metal nanoribbons

We present a systematic density functional theory (DFT) study of the structure and catalytic activity of group 10 (Ni, Pd, Pt) and group 11 (Cu, Ag, Au) coinage metal nanoribbons. These infinite, periodic, quasi‐one‐dimensional structures are conceptually important as intermediates between small metal clusters and close‐packed metal surfaces, and have been shown experimentally to be practical catalysts. We find that nanoribbons have significantly higher predicted H₂ dissociation activity than close‐packed metal surfaces consistent with their lower coordination numbers. Computed periodic trends are reasonable, with late transition states and low barriers for H₂ dissociation over late group 10 nanoribbons, suggesting their promise as practical catalysts. These trends are consistent with the isolated nanoribbons' computed molecular electrostatic potentials. Calculations also predict nearly linear Brønsted–Evans–Polanyi relationships between the nanoribbons' H₂ dissociation energies and dissociation barriers. We also test new meta‐generalized gradient approximation (GGA) and hybrid DFT approximations for H₂ dissociation over these nanoribbons. These new functionals increase the (generally underestimated) dissociation barriers predicted by standard GGAs, motivating their continued application in surface chemistry. © 2015 Wiley Periodicals, Inc.     

Determination of atranol and chloroatranol in perfumes using simultaneous derivatization and dispersive liquid–liquid microextraction followed by gas chromatography–mass spectrometry

A new analytical method based on simultaneous derivatization and dispersive liquid–liquid microextraction (DLLME) followed by gas chromatography–mass spectrometry (GC–MS), for the determination of the allergenic compounds atranol and chloroatranol in perfumes, is presented. Derivatization of the target analytes by means of acetylation with anhydride acetic in carbonate buffer was carried out. Thereby volatility and detectability were increased for improved GC–MS sensitivity. In addition, extractability by DLLME was also enhanced due to a less polar character of the solutes. A liquid–liquid extraction was performed before DLLME to clean up the sample and to obtain an aqueous sample solution, free of the low polar matrix from the essential oils, as donor phase. Different parameters, such as the nature and volume of both the extraction and disperser solvents, the ionic strength of the aqueous donor phase or the effect of the derivatization reagent volume, were optimized. Under the selected conditions (injection of a mixture of 750 μL of acetone as disperser solvent, 100 μL of chloroform as extraction solvent and 100 μL of anhydride acetic as derivatization reagent) the figures of merit of the proposed method were evaluated. Limits of detection in the low ng mL⁻¹ range were obtained. Matrix effect was observed in real perfume samples and thus, standard addition calibration is recommended.     

An optimization‐based undeflated PLS (OUPLS) method to handle missing data in the training set

Advances in sensory systems have led to many industrial applications with large amounts of highly correlated data, particularly in chemical and pharmaceutical processes. With these correlated data sets, it becomes important to consider advanced modeling approaches built to deal with correlated inputs in order to understand the underlying sources of variability and how this variability will affect the final quality of the product. Additional to the correlated nature of the data sets, it is also common to find missing elements and noise in these data matrices. Latent variable regression methods such as partial least squares or projection to latent structures (PLS) have gained much attention in industry for their ability to handle ill‐conditioned matrices with missing elements. This feature of the PLS method is accomplished through the nonlinear iterative PLS (NIPALS) algorithm, with a simple modification to consider the missing data. Moreover, in expectation maximization PLS (EM‐PLS), imputed values are provided for missing data elements as initial estimates, conventional PLS is then applied to update these elements, and the process iterates to convergence. This study is the extension of previous work for principal component analysis (PCA), where we introduced nonlinear programming (NLP) as a means to estimate the parameters of the PCA model. Here, we focus on the parameters of a PLS model. As an alternative to modified NIPALS and EM‐PLS, this paper presents an efficient NLP‐based technique to find model parameters for PLS, where the desired properties of the parameters can be explicitly posed as constraints in the optimization problem of the proposed algorithm. We also present a number of simulation studies, where we compare effectiveness of the proposed algorithm with competing algorithms. Copyright © 2014 John Wiley & Sons, Ltd.     

Thermal and electronic charge transport in bulk nanostructured Zr0.25Hf0.75NiSn composites with full-Heusler inclusions

Bulk Zr_0.25Hf₀₇₅NiSn half-Heusler (HH) nanocomposites containing various mole fractions of full-Heusler (FH) inclusions were prepared by solid state reaction of pre-synthesized HH alloy with elemental Ni at 1073 K. The microstructures of spark plasma sintered specimens of the HH/FH nanocomposites were investigated using transmission electron microscopy and their thermoelectric properties were measured from 300 K to 775 K. The formation of coherent FH inclusions into the HH matrix arises from solid-state Ni diffusion into vacant sites of the HH structure. HH(1–y)/FH(y) composites with mole fraction of FH inclusions below the percolation threshold, y∼0.2, show increased electrical conductivity, reduced Seebeck coefficient and increased total thermal conductivity arising from gradual increase in the carrier concentration for composites. A drastic reduction (∼55%) in κ_l was observed for the composite with y=0.6 and is attributed to enhanced phonon scattering due to mass fluctuations between FH and HH, and high density of HH/FH interfaces.     

Multiple-filled skutterudites: high thermoelectric figure of merit through separately optimizing electrical and thermal transports

Skutterudites CoSb(3) with multiple cofillers Ba, La, and Yb were synthesized and very high thermoelectric figure of merit ZT = 1.7 at 850 K was realized. X-ray diffraction of the densified multiple-filled bulk samples reveals all samples are phase pure. High-resolution scanning transmission electron microscopy (STEM) and energy dispersive X-ray spectroscopy (EDS) analysis confirm that multiple guest fillers occupy the nanoscale-cages in the skutterudites. The fillers are further shown to be uniformly distributed and the Co-Sb skutterudite framework is virtually unperturbed from atomic scale to a few micrometers. Our results firmly show that high power factors can be realized by adjusting the total filling fraction of fillers with different charge states to reach the optimum carrier density, at the same time, lattice thermal conductivity can also be significantly reduced, to values near the glass limit of these materials, through combining filler species of different rattling frequencies to achieve broad-frequency phonon scattering. Therefore, partially filled skutterudites with multiple fillers of different chemical nature render unique structural characteristics for optimizing electrical and thermal transports in a relatively independent way, leading to continually enhanced ZT values from single- to double-, and finally to multiple-filled skutterudites. The idea of combining multiple fillers with different charge states and rattling frequencies for performance optimization is also expected to be valid for other caged TE compounds.     

Measurement of heterogeneous reaction rates: three strategies for controlling mass transport and their application to indium-mediated allylations

We describe three new strategies for determining heterogeneous reaction rates using photomicroscopy to measure the rate of retreat of metal surfaces: (i) spheres in a stirred solution, (ii) microscopic powder in an unstirred solution, and (iii) spheres on a rotating shaft. The strategies are applied to indium-mediated allylation (IMA), which is a powerful tool for synthetic chemists because of its stereoselectivity, broad applicability, and high yields. The rate-limiting step of IMA, reaction of allyl halides at indium metal surfaces, is shown to be fast, with a minimum value of the heterogeneous rate constant of 1 × 10(-2) cm/s, an order of magnitude faster than the previously determined minimum value. The strategies described here can be applied to any reaction in which the surface is retreating or advancing, thereby broadening the applicability of photomicroscopy to measuring heterogeneous reaction kinetics.     

A new azorellane diterpenoid from Azorella madreporica

A new azorellane diterpenoid has been isolated and identified from the aerial parts of Azorella madreporica Clos. The structure of 1 was established by one- and two-dimensional NMR techniques.     

Homeomorphisms of the annulus with a transitive lift

Let f be a homeomorphism of the closed annulus A that preserves the orientation, the boundary components and that has a lift ${\tilde{f}}$ to the infinite strip à which is transitive. We show that, if the rotation numbers of both boundary components of A are strictly positive, then there exists a closed nonempty unbounded set ${B^{-} \subset \tilde{A}}$ such that B ^? is bounded to the right, the projection of B ^? to A is dense, ${B^{-}-(1, 0) \subset B^{-}}$ and ${\tilde{f}(B^{-}) \subset B^{-}}$ . Moreover, if p ₁ is the projection on the first coordinate of Ã, then there exists d > 0 such that, for any ${\tilde z \in B^{-}}$ , $$\limsup_{n\to\infty}\frac{p_1(\tilde f^n(\tilde z))-p_1(\tilde z)}{n}<-d.$$ In particular, using a result of Franks, we show that the rotation set of any homeomorphism of the annulus that preserves orientation, boundary components, which has a transitive lift without fixed points in the boundary is an interval with 0 in its interior.     

Alcohol and metal determination in alcoholic beverages through high-temperature liquid-chromatography coupled to an inductively coupled plasma atomic emission spectrometer

In the present work, an inductively coupled plasma atomic emission spectrometry (ICP-AES) system was used as a high temperature liquid chromatography (HTLC) detector for the determination of alcohols and metals in beverages. For the sake of comparison, a refractive index (RI) detector was also employed for the first time to detect alcohols with HTLC. The organic compounds studied were methanol, ethanol, propan-1-ol and butan-1-ol (in the 10-125 mg/L concentration range) and the elements tested were magnesium, aluminum, copper, manganese and barium at concentrations included between roughly 0.01 and 80 mg/L. Column heating temperatures ranged from 80 to 175 °C and the optimum ones in terms of peak resolution, sensitivity and column lifetime were 125 and 100 °C for the HTLC-RI and HTLC-ICP-AES couplings, respectively. The HTLC-ICP-AES interface design (i.e., spray chamber design and nebulizer type used) was studied and it was found that a single pass spray chamber provided about 2 times higher sensitivities than a cyclonic conventional design. Comparatively speaking, limits of detection for alcohols were of the same order for the two evaluated detection systems (from 5 to 25 mg/L). In contrast, unlike RI, ICP-AES provided information about the content of both organic and inorganic species. Furthermore, temperature programming was applied to shorten the analysis time and it was verified that ICP-AES was less sensitive to temperature changes and modifications in the analyte chemical nature than the RI detector. Both detectors were successfully applied to the determination of short chain alcohols in several beverages such as muscatel, pacharan, punch, vermouth and two different brands of whiskeys (from 10 to 40 g of ethanol/100 g of sample). The results of the inorganic elements studied by HTLC-ICP-AES were compared with those obtained using inductively coupled plasma mass spectrometry (ICP-MS) obtaining good agreement between them. Recoveries found for spiked samples were close to 100% for both, inorganic elements (with both HLTC-ICP-AES and ICP-MS) and alcohols (with both HTLC-ICP-AES and HTLC-RI hyphenations).