Norberto Casillas

Structure of reverse microemulsion-templated metal hexacyanoferrate nanoparticles

The droplet phase of a reverse microemulsion formed by the surfactant cetyltrimethylammonium ferrocyanide was used as a matrix to synthesize nanoparticles of nickel hexacyanoferrate by adding just a solution of NiCl2 to the microemulsion media. Dynamic light scattering and small-angle neutron scattering measurements show that the reverse microemulsion droplets employed have a globular structure, with sizes that depend on water content. Transmission electron microscopy and electron diffraction are used to obtain information about the structure of the synthesized nanoparticles. The results show that the size and shape of the coordination compound nanoparticles correspond with the size and shape of the droplets, suggesting that the presented system constitutes an alternative method of the synthesis of metal hexacyanoferrate nanoparticles.

Determination of Cu in Tequila by Anodic Stripping Voltammetry

Abstract Concentrations of metals such as copper in alcoholic beverages must be strictly regulated due to negative effects ranging from beverage spoilage and hazing, to sensorial and health consequences. In this paper, a voltammetric alternative is presented for the analysis of copper in tequila, a Mexican spirituous alcoholic beverage. Anodic Stripping Voltammetry is applied and the standard addition method is used to quantify copper in this beverage at concentrations commonly present in tequila (<10 ppm) without sample pretreatment. Copper can be reduced and then oxidized quantitatively and reproducibly. A comparison of Anodic Stripping Voltammetry with Atomic Absorption Spectrometry is presented.

Carbon nanotubes/carbon xerogel-nafion electrodes: a comparative study of preparation methods

We report the preparation and electrochemical characterization of carbon nanotubes (CNT)/carbon xerogel-nafion (CXN) electrodes obtained by casting carbon nanotube inks on carbon xerogel-nafion matrixes under terrestrial (g) and enhanced (13 g) gravity. The impregnated electrodes were compared with composites prepared by mixing CXN dispersions with CNT inks. For casted CNT, alternate current scanning electrochemical microscopy studies along the film-electrode area showed differences that can be correlated with the position of the electronic conducting CNT phase on the more resistive matrix. It revealed the transition from a conductive to dielectric surface when impregnation takes place at terrestrial and enhanced gravity, respectively. Although the addition of CNT enhances the capacitance and mechanical properties of CXN in all preparation methods, the largest specific capacitance was observed in electrodes impregnated at 1 g. Electrodes prepared by mixing and those casted at 13 g show similar capacitance values regardless of contrasting conductivity. A mechanism explaining the microstructural, electrical, and adsorptive differences brought out by the various preparation methods is proposed.

Assessment of Physicochemical Properties of Tequila Brands: Authentication and Quality

Several physicochemical properties were measured in commercial tequila brands: conductivity, density, pH, sound velocity, viscosity, and refractive index. Physicochemical data were analyzed by Principal Component Analysis (PCA), cluster analysis, and the one-way analysis of variance to identify the quality and authenticity of tequila brands. According to the Principal Component Analysis, the existence of 3 main components was identified, explaining the 87.76% of the total variability of physicochemical measurements. In general, all tequila brands appeared together in the plane of the first two principal components. In the cluster analysis, four groups showing similar characteristics were identified. In particular, one of the clusters contains some tequila brands that are not identified by the Regulatory Council of Tequila and do not meet the quality requirements established in the Mexican Official Standard 006. These tequila brands are characterized by having higher conductivity and density and lower viscosity and refractive index, determined by one-way analysis of variance. Therefore, these economical measurements, PCA, and cluster analysis can be used to determinate the authenticity of a tequila brand.

Obtaining NiHCF Nanoparticles Using a Reverse Micellar System

The synthesis of metallic nanoparticles using a reverse microemulsion medium brings controlled size and shape. In this study, reverse micelar system was employed for the synthesis of nickel hexacyanoferrate nanoparticles, NiHCF, by direct encapsulation in the water pools of reverse micelles formed in a pseudoternary system that consist of a mixture of 95 %wt. cetyltrimetyl ammonium bromide (CTAB) and 5 %wt. of a novel modified surfactant cetyltrimetyl ammonium ferrocyanate (CTA[Fe(CN6)]4-, CTAFe)/n-butanol/Hexane/Water. These NiHCF nanoparticles were produced with particle size ranging with 20 – 60 nm.

Data for the paper: The importance of the film structure during self-powered ibuprofen salicylate drug release from polypyrrole electrodeposited on AZ31 Mg

Therapeutic drugs uploaded into conjugated conductive polymer matrices deposited on active magnesium alloys serve as controlled-dose, self-powered drug-delivery systems. Preferentially, drugs are added into polymer films in the largest amount possible, mostly to prevent long-term treatments. However, added drugs might interact with the polymer matrix affecting either the structure or the final mechanical properties of the polymer film. In this work, polypyrrole films (PPy) electrodeposited on an AZ31 Mg alloy in ibuprofen and salicylate-containing solutions are investigated in terms of their uploading capacity, surface morphology, and mechanical properties. The techniques used to investigate the uploaded PPy films include cyclic voltammetry (CV), scanning electron microscopy (SEM), EDS, and depth-sensing indentation (DSI). A maximum ibuprofen concentration of 440 ± 40 ?g cm?2 was obtained in PPy films in the presence of sodium salicylate. The release fraction of ibuprofen as a function of time is fitted to Avrami’s equation. The hardness and reduced modulus decreased by 54 and 40 %, respectively, when the Ppy films are prepared in the presence of sodium ibuprofen compared with those prepared in sodium salicylate only, indicating a more plastic film with ibuprofen

Amperometric Titration of Fructan Oligosaccharides of Agave Tequilana Webber, Blue Variety, in a Rotating Disk Electrode.

Centro de Investigacion y Asistencia en Tecnologia y Diseno del Estado de Jalisco (CIATEJ), Guadalajara, Jalisco, 44270, Mexico. This paper deals with a simple, rapid and sensitive method for quantifying oligosaccharides of fructans of Agave Tequilana Webber a Blue Variety. The method is based on the oxidation of the carbonyl group of the oligosaccharide in its linear open-ring with ferricyanide ions in a RDE (rotating disk electrode). The amperometric titration is carried out at different temperatures, e.g., 60, 65, 70, 75, 80 and 85 °C as a strategy to control the amount of oligosaccharides with the open-ring as a function of their molecular size. The proposed method allows us to determine concentrations of oligosaccharides as low as 0.71 mM. A calibration curve between the limiting current of the Fe(CN)

Heuristic correlation of rheological measurements and Electrochemical Impedance Spectroscopy (EIS) of the DNA/water system.

In this work, it is reported viscosity, density, sound velocity and electrochemical impedance spectroscopy (EIS) measurements of calf thymus DNA in aqueous solutions, in order to investigate the overlapping C* and entanglement concentrations Ce. These critical concentrations demark the conditions at which start appearing interactions and entanglements between DNA molecules in solution. EIS has been proposed as new alternative analytical techniques to obtain C* and Ce in polyelectrolyte solutions. A new parameter the characteristic time (τc) was defined, and it is obtained from a new type of log-log Bode plot using the crossover frequency (τc=1/ωc) of the real (Z’) and imaginary (Z”) components when they are plotted as a function of the frequency. Preliminary results show similar values C* and Ce by EIS to those obtained from rheological, densimetry and sound velocity measurements.

Localized Impedance Measurements in Different Redox Potential Metals and their Galvanic Coupling by Using AC-SECM

In recent years, the use of Scanning Electrochemical Microscopy in its Alternating Current mode (AC-SECM) has increased due to its capability for detecting and interpreting local variations of electrochemical properties on surfaces with high spatial resolution. In this paper, we intend to extend the applications of AC-SECM for identifying local impedance variations on surfaces of materials with different redox potential, immersed in resistive media such as tequila in presence of supporting electrolyte. Preliminary results are promising since it is possible to visualize boundaries of materials with different redox potential by means of localized impedance measurements, which opens a new perspective for studying composite materials such as minerals.

Comparison of a Joule effect calibration system using Kanthal wire and a laser diode as heat sources

Here it is presented a comparison of two calibration techniques applied to a thermistor element used in a surface microcalorimeter which operates under Isoperibol conditions. Usually surface microcalorimeters employ a thermistor as a temperature sensing element, whose heat capacity requires to be evaluated before they can be used. One alternative method to estimate its heat capacity is by supplying a known amount of energy and detecting its temperature changes. Thus, surface heating can be achieved by different techniques; one of them is by supplying energy to the thermistor by passing current through a Ni-Cr coil wined around the glass bulb thermistor. A rather different and more convenient technique consists of directly illuminating a small well-defined thermistor area with an infrared 1550 nm wavelength laser beam, while detecting the thermistor temperature changes. Both procedures are thoroughly compared and the heat capacities obtained by both methods are presented.