Feasibility of a Nano‐Carbon Black Paste Electrode for Simultaneous Voltammetric Determination of Antioxidants in Food Samples and Biodiesel in the Presence of Surfactant

In this work, a simple and low‐cost method was developed for the simultaneous determination of the antioxidants tert‐butylhydroquinone (TBHQ) and butylated hydroxyanisole (BHA) in the presence of the cationic surfactant CPB by square wave voltammetry (SWV) technique using a carbon black paste electrode (CBPE). The performance of the method was investigated by varying parameters such as pH, electrolyte, and type and concentration of surfactant. Under the optimum conditions of 0.2 mol L^?1 phosphate buffer (pH 7.0), 600.0 μmol L^?1 of cetylpyridinium bromide surfactant and SWV operating parameters optimized through the Doehlert matrix, the method presented low limits of quantification for TBHQ and BHA (0.23 and 0.26 μmol L^?1, respectively) and high precision in successive measurements. The proposed method was applied in mayonnaise, margarine and biodiesel and the accuracy of method was checked by the HPLC technique.     

On a family of non-oscillatory subdivision schemes having regularity Cr with r > 1

Numerical Algorithms - In this paper, the properties of a new family of nonlinear dyadic subdivision schemes are presented and studied depending on the conditions imposed to the mean used to...     

Influence of structural transformations over the electrochemical behavior of Ti anodic films grown in 0.1 M NaOH

In this work, the structural transformation during the anodic growth of Ti oxide films and its influence on the resistive properties of the film are studied. The voltammetric characterization of Ti/0.1 M NaOH indicates that the oxide film composition depends on potential. Depending on the anodic switching potential, the oxide film can produce up to three cathodic peaks, and the peaks can be related to different Ti oxides. During the early stages of potentiostatic formation, the oxide film seems to have the same initial structure regardless of the film formation potential; however, after increasing growth time, the oxide structure depends on the formation potential. The evaluation of the resistive properties of Ti oxide films determined by electrochemical impedance spectroscopy shows that despite the chemical transformations within the film, there is a linear dependence between the capacitance of the Ti oxide film with formation potential.     

Variable neighbourhood search for bandwidth reduction

The problem of reducing the bandwidth of a matrix consists of finding a permutation of rows and columns of a given matrix which keeps the non-zero elements in a band as close as possible to the main diagonal. This NP-complete problem can also be formulated as a vertex labelling problem on a graph, where each edge represents a non-zero element of the matrix. We propose a variable neighbourhood search based heuristic for reducing the bandwidth of a matrix which successfully combines several recent ideas from the literature. Empirical results for an often used collection of 113 benchmark instances indicate that the proposed heuristic compares favourably to all previous methods. Moreover, with our approach, we improve best solutions in 50% of instances of large benchmark tests.     

Guest-controlled aggregation of cavitand gold nanoparticles and N-methyl pyridinium-terminated PEG

The introduction of a disulfide functionalized tetraphosphonate cavitand on Au nanoparticles promotes the reversible self-assembly of a hybrid network upon addition of a polymeric ditopic guest.     

Characterisation of an exothermic reaction using adiabatic and isothermal calorimetry

A simple esterification reaction is used to demonstrate standard procedures for determining the thermokinetic parameters of an exothermic reaction from adiabatic calorimetric data. The influence of variations in the heat capacity of the sample due to changes in temperature and concentration is explored. Shortcomings in the simple interpretation of adiabatic data are identified and isothermal heatflow calorimetry is used to reveal autocatalytic effects which were not apparent from the adiabatic experiments. A more rigourous interpretation of the adiabatic and isothermal data is outlined and used to predict the conditions which can lead to exothermic runaway in a batch reactor. Mathematical simulation of the conditions in a jacketed reactor is used to demonstrate the importance of developing reliable kinetic expressions before assessing the safety of a batch process.

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Zusammenfassung Anhand einer einfachen Veresterungsreaktion wurden Standardverfahren zur Ermittlung thermokinetischer Parameter exothermen Reaktionen aus adiabatischen kalorimetrischen Daten demonstriert. Dabei wurde der Einfluß von Temperatur und Konzentration auf Änderungen der Wärmekapazität untersucht. Fehler bei der einfachen Interpretation adiabatischer Daten wurden identifiziert und isotherme Wärmeflußkalorimetrie wurde angewendet, um autokatalytische Effekte aufzuzeigen, die sich anhand der adiabatischen Experimente nicht ersehen lassen. Es wurde eine gründlichere Interpretation adiabatischer und isothermer Daten umrissen und verwendet, um die Bedingungen vorherzusagen, die in einem Kesselreaktor zu einem exothermen Davonlaufen der Reaktion führen. Mathematische Simulation der Bedingungen in einem Mantelkessel wurde angewendet, um zu zeigen, von welch großer Bedeutung die Entwicklung zuverlässiger kinetischer Ausdrücke ist, bevor man die Sicherheit einer Reaktion in einem Kesselreaktor beurteilt.

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Cavitand-functionalized SWCNTs for N-methylammonium detection

Single-walled carbon nanotubes (SWCNTs) have been functionalized with highly selective tetraphosphonate cavitand receptors. The binding of charged N-methylammonium species to the functionalized SWCNTs was analyzed by X-ray photoelectron spectroscopy and confirmed by (31)P MAS NMR spectroscopy. The cavitand-functionalized SWCNTs were shown to function as chemiresistive sensory materials for the detection of sarcosine and its ethyl ester hydrochloride in water with high selectivity at concentrations as low as 0.02 mM. Exposure to sarcosine and its derivative resulted in an increased conductance, in contrast to a decreased conductance response observed for potential interferents such as the structurally related glycine ethyl ester hydrochloride.