Determination of acetaldehyde in fuel ethanol by high-performance liquid chromatography with electrochemical detection

The cyclic voltammetric behavior of acetaldehyde and the derivatized product with 2,4-dinitrophenylhydrazine (DNPHi) has been studied at a glassy carbon electrode. This study was used to optimize the best experimental conditions for its determination by high-performance liquid chromatographic (HPLC) separation coupled with electrochemical detection. The acetaldehyde-2,4-dinitrophenyl.hydrazone (ADNPH) was eluted and separated by a reversed-phase column, C-18, under isocratic conditions with the mobile phase containing a binary mixture of methanol/LiCl(aq) at a concentration of 1.0 x 10(-3) M (80:20 v/v) and a flow rate of 1.0 mL min(-1). The optimum condition for the electrochemical detection of ADNPH was +1.0 V vs. Ag/AgCl as a reference electrode. The proposed method was simple, rapid (analysis time 7 min) and sensitive (detection limit 3.80 mu g L-1) at a signal-to-noise ratio of 3:1. It was also highly selective and reproducible [standard deviation 8.2% +/- 0.36 (n = 5)]. The analytical curve of ADNPH was linear over the range of 3-300 mg L-1 per injection (20 mu L), and the analytical recovery was > 99%.

Determination of aldehydes and ketones in fuel ethanol by high-performance liquid chromatography with electrochemical detection

A new methodology was developed for analysis of aldehydes and ketones in fuel ethanol by high-performance liquid chromatography (HPLC) coupled to electrochemical detection. The electrochemical oxidation of 5-hydroxymetkylfurfural, 2-furfuraldehyde, butyraldehyde, acetone and methyl ethyl ketone derivatized with 2,4-dinitrophenylhydrazine (DNPH) at glassy carbon electrode present a well defined wave at +0.94 V; +0.99 V; +1.29 V; +1.15 V and +1.18 V, respectively which are the basis for its determination on electrochemical defector. The carbonyl compounds derivatized were separated by a reverse-phase column under isocratic conditions with a mobile phase containing a binary mixture of methanol /LiClO4(aq) at a concentration of 1.0 x 10(-3) mol L-1 (80:20 v/v) and a flow-rate of 1.1 mL min(-1). The optimum potential for the electrochemical detection of aldehydes-DNPH and ketones-DNPH was +1.0 V vs. Ag/AgCl. The analytical curve of aldehydes-DNPH and ketones-DNPH presented linearity over the range 5.0 to 400.0 ng mL(-1), with detection limits of 1.7 to 2.0 ng mL(-1) and quantification limits from 5.0 to 6.2 ng mL(-1), using injection volume of 20 mu L. The proposed methodology was simple, low time-consuming (15 min/analysis) and presented analytical recovery higher than 95%.

BaZrO3 Photoluminescence Property: An Ab Initio Analysis of Structural Deformation and Symmetry Changes

This article reports a theoretical study based on experimental results for barium zirconate, BaZrO3 (BZ) thin films, using periodic mechanic quantum calculations to analyze the symmetry change in a structural order-disorder simulation. Four periodic models were simulated using CRYSTAL98 code to represent the ordered and disordered BZ structures. The results were analyzed in terms of the energy level diagrams and atomic orbital distributions to explain and understand the BZ photoluminescence properties (PL) at room temperature for the disordered structure based on structural deformation and symmetry changes. (C) 2009 Wiley Periodicals, Inc. Int J Quantum Chem 111: 694-701, 2011

Electrochemical behavior of cobalt oxide coatings on cold-rolled steel in alkaline sodium sulfate

The electrochemical behavior of a coating of cobalt oxide on cold-rolled steel in alkaline sodium sulfate was Studied using the electrochemical techniques of open-circuit potential measurements and electrochemical impedance spectroscopy. The coating was prepared at different annealing temperatures ranging from 350 to 750 degreesC and characterized by SEM, EDX and XRD. Below 550 degreesC the composition of the coating was basically of Co3O4. At 750 degreesC CoO was formed and big cracks appeared on the film exposing an inner layer of iron oxides. Analysis of the EIS data is very difficult because of the complexity of the interface structure. It can be inferred that the charge transfer resistance of the coatings prepared at 350 and 450 C were higher than those for the coatings prepared at temperatures above 550 degreesC. (C) 2002 Published by Elsevier B.V. Ltd.

Influence of the heat treatment in the electrochemical corrosion of Al-Zn-Mg alloys

The localized corrosion of Al-(5.03%)Zn-(1.67%)Mg-(0.23%)Cu alloys and high purity Al has been studied using electrochemical techniques, optical microscopy, SEM and EDX. The samples were previously submitted to different heat treatments in which coherent and incoherent MgZn 2 precipitates with different distribution and aggregation degree were produced. The influence of NaCl and Na 2SO 4, dissolved oxygen, immersion time and convection were studied. In NaCl solutions, pitting potentials for the alloys were more negative than for aluminium, indicating an increase in their susceptibility to localized corrosion. Moreover, annealed and cold-rolled alloys presented more negative pitting and repassivation potentials than those submitted to age hardening with direct or interrupted quenching. In annealed and cold-rolled samples, pit nucleation and propagation takes place in the zones where MgZn 2 is accumulated. In the case of the age-hardened alloys, a double pitting behaviour is observed, the first one in the magnesium and zinc enriched regions and the second in the matrix. While the cold water quenched alloy is susceptible to stress corrosion craking, the alloy submitted to the interrupted quenching process is less susceptible to intergranular attack. The sulphate ion shifts the pitting potential of aluminium and the alloys by chloride towards more positive values because it impedes local accumulations of the latter. © 1992 Chapman & Hall.

Estudio de la pasivacion de la aleacion Co-Cr-Mo en suero fisiologico

Results are presented on the mechanism of passivation of Co-Cr-Mo biological implant alloys in physiological serum using open circuit potentiometry, potentiodynamic curves, and electrochemical impedance spectroscopy. The potential dependence of impedance data and the analysis of the parameters obtained indicate a progressive diminution of the initial layer thickness and the simultaneous formation of a second higher resistive layer. In more severe conditions than the existent in human body, the metallographic examination of the alloy surface shows localized corrosion in interdendritric regions. Elemental analysis of the surface reveals the presence of higher chromium content in these regions. The presence of chlorine was not detected, which suggested that during preferential attack, soluble species are also formed.

Variation in mandible shape in Thrichomys apereoides (Mammalia: Rodentia): Geometric analysis of a complex morphological structure

The model of development and evolution of complex morphological structures conceived by Atchley and Hall in 1991 (Biol. Rev. 66:101-157), which establishes that changes at the macroscopic, morphogenetic level can be statistically detected as variation in skeletal units at distinct scales, was applied in combination with the formalism of geometric morphometrics to study variation in mandible shape among populations of the rodent species Thrichomys apereoides. The thin-plate spline technique produced geometric descriptors of shape derived from anatomical landmarks in the mandible, which we used with graphical and inferential approaches to partition the contribution of global and localized components to the observed differentiation in mandible shape. A major pattern of morphological differentiation in T. apereoides is attributable to localized components of shape at smaller geometric scales associated with specific morphogenetic units of the mandible. On the other hand, a clinal trend of variation is associated primarily with localized components of shape at larger geometric scales. Morphogenetic mechanisms assumed to be operating to produce the observed differentiation in the specific units of the mandible include mesenchymal condensation differentiation, muscle hypertrophy, and tooth growth. Perspectives for the application of models of morphological evolution and geometric morphometrics to morphologically based systematic biology are considered.

Microstructural characteristics and electrochemical behavior of Co3O4 sintered electrodes

Co3O4 can be used as electrocatalyst for oxygen evolution reaction. The macro and microstructure of the oxide, obtained by compacting and sintering lithium-doped Co3O4 powder in atmosphere of dry air and in conditions of controlled temperature and time was analyzed by metallographic techniques. The porous material was characterized by XRD, SEM and EDS combined techniques. For working temperatures up to 1200°C, the pellet was consituted of particles with varying sizes over a wide range of particle size and, at higher temperatures CoO is formed and polymorphic transformation was observed. The materials were also characterized electrochemically in alkaline media by open circuit potential and potentiodynamic I/E measurements. The results were compared to those previously prepared by others by thermal deposition.

Economical analysis of ethanol steam reformer for hydrogen production associated with a sugarcane industry

An expressive amount of produced hydrogen is generated by customers in-situ such as petrochemical, fertilizer and sugarcane industries. However, the most utilized feedstock is natural gas, a non-renewable and fossil fuel. The introduction of biohydrogen production process associated in a sugarcane industry is an alternative to diminish emissions and contribute to create a CO2 cycle, where the plants capture this gas by photosynthesis process and produces sucrose for ethanol production. The cost of production of ethanol has dramatically decreased (from about US$ 700/m3 in 1970s to US$ 200/m3 today), becoming this a good option at near term, inclusively for its utilization by customers localized in main regions (localized especially in regions such as Southeastern Brazil) Also in near future, it will possible the utilization of fuel cells as form of distributed generation. Its utilization could occur specially in peak hours, diminishing the cost of investments in newer transmission systems. A technical and economic analysis of steam reformer of ethanol to hydrogen production associated with sugarcane industry was recently performed. This technique will also allow the use of ethanol when its price is relatively low. This study was based on a previous R&D study (sponsored by CEMIG - State of Minas Gerais Electricity Company) where thermodynamic and economic analyses were developed, based in the development of two ethanol steam reformers prototypes.x In this study an analysis was performed considering the use of bagasse as source of heat in the steam reforming process. Its use could to diminish the costs of hydrogen production, especially at large scale, obtaining cost-competitive production and permitting that sugarcane industry produces hydrogen in large scale beyond ethylic alcohol, anhydrous alcohol (or ethanol) and sugar.

Integrated analysis of halogenated organic pollutants in sub-millilitre volumes of venous and umbilical cord blood sera

A rapid, robust and economical method for the analysis of persistent halogenated organic compounds in small volumes of human serum and umbilical cord blood is described. The pollutants studied cover a broad range of molecules of contemporary epidemiological and legislative concern, including polychlorobiphenyls (PCBs), polychlorobenzenes (CBs), hexachlorocyclohexanes (HCHs), DDTs, polychlorostyrenes (PCSs) and polybromodiphenyl ethers (PBDEs). Extraction and clean-up with n-hexane and concentrated sulphuric acid was followed with analysis by gas chromatography coupled to electron capture (GC-ECD) and GC coupled to negative ion chemical ionisation mass spectrometry (GC-NICI-MS). The advantages of this method rest in the broad range of analytes and its simplicity and robustness, while the use of concentrated sulphuric acid extraction/clean-up destroys viruses that may be present in the samples. Small volumes of reference serum between 50 and 1000 μL were extracted and the limits of detection/quantification and repeatability were determined. Recoveries of spiked compounds for the extraction of small volumes (≥300 μL) of the spiked reference serum were between 90% and 120%. The coefficients of variation of repeatability ranged from 0.1-14%, depending on the compound. Samples of 4-year-old serum and umbilical cord blood (n = 73 and 40, respectively) from a population inhabiting a village near a chloro-alkali plant were screened for the above-mentioned halogenated pollutants using this method and the results are briefly described. © 2010 Springer-Verlag.

Electrochemical determination of antimalarial drug amodiaquine in maternal milk using a hemin-based electrode

Voltammetric analysis of amodiaquine using a hemin biosensor revealed a well-defined peak at 0.14 V (vs. Ag/AgCl), corresponding to the oxidation of amodiaquine at pH 7.0. The electrodic behavior indicated that the oxidation process was irreversible, and that it was controlled by diffusion. In addition to advantages such as high selectivity and sensitivity, the method developed could be used for the analysis of breast milk containing amodiaquine without any need for prior sample treatment, an important consideration in routine analysis laboratories. Measurements of the drug contained in breast milk were used to validate the technique. The detection limit for standard solutions was 3.30 mg L-1, and the quantification limit was 11.0 mg L-1. ©The Electrochemical Society.

An optimised electrochemical biosensor for the label-free detection of C-reactive protein in blood

C-reactive protein (CRP) is an acute phase protein whose levels are increased in many disorders. There exists, in particular, a great deal of interest in the correlation between blood serum levels and the severity of risk for cardiovascular disease. A sensitive, label-free, non-amplified and reusable electrochemical impedimetric biosensor for the detection of CRP in blood serum was developed herein based on controlled and coverage optimised antibody immobilization on standard polycrystalline gold electrodes. Charge transfer resistance changes were highly target specific, linear with log. CRP. concentration across a 0.5-50. nM range and associated with a limit of detection of 176. pM. Significantly, the detection limits are better than those of current CRP clinical methods and the assays are potentially cheap, relatively automated, reusable, multiplexed and highly portable. The generated interfaces were capable not only of comfortably quantifying CRP across a clinically relevant range of concentrations but also of doing this in whole blood serum with interfaces that were, subsequently, reusable. The importance of optimising receptor layer resistance in maximising assay sensitivity is also detailed. © 2012.

Electrochemical studies based on local interfacial ph changes of gold nanoparticles immobilized on polystyrene brushes

The electrochemical behavior of polystyrene modified with gold nanoparticle (Au NPs) was investigated in terms of pH-responsive polymer brush. A pH-responsive of modified polymer brush from tethered polystyrene was prepared and used for selective gating transport of anions andcations across the thin-film. An ITO-coated glass electrode was used as substrate and applied to study the switchable permeability of the polymer brush triggered by changes in pH of the aqueous environment. The pH-sensitive behavior of the polymer brush interface has been demonstrated by means of cyclic voltammetry (CV) and Localized Surface Plasmon Resonance (LSPR). CV experiments showed at ph values of 4 and 8 induces swelling and shrinking of the grafted polymer brushes, respectively, and this behavior is fast and reversible. LSPR measurements showed a blue shift of 33 nm in the surface resonance band changes by local pH. The paper brings an easy methodology to fabrication a variety of nanosensors based on the polymer brushes-nanoparticle assemblies. © 2013 by ESG.

Development of an electrochemical sensor based on nanostructured hausmannite-type manganese oxide for detection of sodium ions

The preparation and electrochemical characterization of hausmannite-type manganese oxide to use as a sensing material for sodium ion is described. This paper reports a new via synthetic to obtain of the hausmannite-type manganese oxide and its application in the construction of modified electrode as a voltammetric sensor. The electrochemical activity of hausmannite-type manganese oxide is controlled by intercalation/deintercalation of the sodium ions within the oxide lattice. The detection is based on the measurement of anodic current generated by oxidation of MnIII-MnIV at electrode surface. The best electrochemical response was obtained for a sensor composition of 20% (w/w) hausmannite oxide in the paste, a TRIS buffer solution of pH 6.0-7.0 and a scan rate of 50 mV s-1. A sensitive linear voltammetric response for sodium ions was obtained in the concentration range of 2.01 × 10 -5-2.09 × 10-4 mol L-1 with a slope of 355 μA L mmol-1 and a detection limit of 7.50 × 10 -6 mol L-1 using cyclic voltammetry. The use of hausmannite has significantly improved the selectivity of the sensor compared to the birnessite-type manganese oxide modified electrode. Under the working conditions, the proposed method was successfully applied to determination of sodium ions in urine samples. © 2013 Elsevier B.V.

Use of conventional electrochemical techniques to produce crystalline FeRh alloys induced by Ag seed layer

By combining galvanic displacement and electrodeposition techniques, an ordered Fe20Rh80 structure deposited onto brass was investigated by X-ray diffractometry, Mössbauer spectroscopy and magnetization measurements. Mössbauer and X-ray diffraction analyses suggest that the Fe-Rh alloy directly electrodeposited onto brass displays a nanocrystalline state while a similar alloy deposited onto Ag/brass shows a faced centered cubic-like structure, with dendrites-like features. These results directly indicate that the presence of Ag seed layer is responsible for the Fe-Rh alloy crystallization process. In addition, room temperature Mössbauer data indicate firstly paramagnetic states for two Fe-species. In the dominant Fe-species (major fraction of the Mössbauer spectra), Fe atoms are situated at a cubic environment and it can be attributed to the γ-Fe20Rh80 alloy based on their hyperfine parameters. In the second species, Fe atoms are placed in a non-local symmetry, which can be related to Fe atoms at the grain boundaries or/and Fe small clusters. These Fe-clusters are in superparamagnetic state at room temperature, but they may be ordered below 45 K, as suggested by magnetization data. © 2013 Elsevier B.V. All rights reserved.