Electrochemical oxidation of propanil and related N-substituted amides

The electrochemical behaviour of propanil and related N-substituted amides (acetanilide and N,N-diphenylacetamide) was studied by cyclic and square wave voltammetry using a glassy carbon electrode. Propanil has been found to have chemical stability under the established analytical conditions and showed an oxidation peak at +1.27V versus Ag/AgCl at pH 7.5. N,N-diphenylacetamide has a higher oxidation potential than the other compounds of +1.49V versus Ag/AgCl. Acetanilide oxidation occurred at a potential similar to that of propanil, +1.24V versus Ag/AgCl. These results are in agreement with the substitution pattern of the nitrogen atom of the amide. A degradation product of propanil, 3,4-dichloroaniline (DCA), was also studied, and showed an oxidation peak at +0.66V versus Ag/AgCl. A simple and specific quantitative electroanalytical method is described for the analysis of propanil in commercial products that contain propanil as the active ingredient, used in the treatment of rice crops in Portugal.

Electrochemical determination of citalopram by adsorptive stripping voltammetry–determination in pharmaceutical products

The electrochemical behavior of citalopram was studied by square-wave and square-wave adsorptive-stripping voltammetry (SWAdSV). Citalopram can be reduced and accumulated at a mercury drop electrode, with a maximum peak current intensity being obtained at a potential of approximately -1.25V vs. AgCl/Ag, in an aqueous electrolyte solution of pH 12. A SWAdSV method has been developed for the determination of citalopram in pharmaceutical preparations. The method shows a linear range between 1.0x10-7 and 2.0x10-6 mol L-1 with a limit of detection of 5x10-8 mol L-1 for an accumulation time of 30 s. The precision of the method was evaluated by assessing the repeatability and intermediate precision, achieving good relative standard deviations in all cases (≤2.3%). The proposed method was applied to the determination of citalopram in five pharmaceutical products and the results obtained are in good agreement with the labeled values.

Flow injection electrochemical determination of apomorphine

Few analytical methods are currently available for determination of apomorphine, the active substance of a new oral formulation used in the treatment of erectile dysfunction. In this way a flow injection electrochemical method (FIA-EC) was developed for its quantification and applied to pharmaceutical dosage forms. Based in previous findings regarding the stability of apomorphine in borate buffer and after optimization of several analytical parameters a single channel flow injection manifold was set up that enables the determination of this drug over the concentration range of 3 to 16 µmol L-1 with a detection limit of 0.5 µmol L-1 at a sampling rateof 90 h-1. The simplicity and rapidity of the FIA-EC method used, its reproducibility and sensitivity make it suitable for quality control of pharmaceutical preparations of apomorphine intended for clinical use and research.

Nanohybrid materials as transducer surfaces for electrochemical sensing applications

A nanohybrid electrochemical transducer surface was developed using carbon and gold nanomaterials. The strategy relayed on casting multiwalled carbon nanotubes or carbon nanofibers onto a screen-printed carbon electrode surface, followed by in situ generation of gold nanoparticles by electrochemical deposition of ionic gold, in a reproducible manner. These transducers, so fabricated, were characterized using both electrochemical and microscopic techniques. Biofunctionality was evaluated using the streptavidin-biotin interaction system as the biological reaction model. These platforms allow to achieve low detection limits (in the order of pmoles), are reproducible and stable at least for a month after their preparation, being a perfect candidate to be used as transducer of different sensor devices.

Electrochemical determination of dihydrocodeine in pharmaceuticals

Two analytical methods for the quality control of dihydrocodeine in commercial pharmaceutical formulations have been developed and compared with reference methods: a square wave voltammetric (SWV) method and a flow injection analysis system with electrochemical detection (FIA-EC). The electrochemical methods proposed were successfully applied to the determination of dihydrocodeine in pharmaceutical tablets and in oral solutions. These methods do not require any pretreatment of the samples, the formulation only being dissolved in a suitable electrolyte. Validation of the methods showed it to be precise, accurate and linear over the concentration range of analysis. The automatic procedure based on a flow injection analysis manifold allows a sampling rate of 115 determinations per hour.

Electrochemical DNA-sensor for evaluation of total antioxidant capacity of flavours and flavoured waters using superoxide radical damage

In this paper, a biosensor based on a glassy carbon electrode (GCE) was used for the evaluation of the total antioxidant capacity (TAC) of flavours and flavoured waters. This biosensor was constructed by immobilising purine bases, guanine and adenine, on a GCE. Square wave voltammetry (SWV) was selected for the development of this methodology. Damage caused by the reactive oxygen species (ROS), superoxide radical (O2·−), generated by the xanthine/xanthine oxidase (XOD) system on the DNA-biosensor was evaluated. DNA-biosensor encountered with oxidative lesion when it was in contact with the O2·−. There was less oxidative damage when reactive antioxidants were added. The antioxidants used in this work were ascorbic acid, gallic acid, caffeic acid, coumaric acid and resveratrol. These antioxidants are capable of scavenging the superoxide radical and therefore protect the purine bases immobilized on the GCE surface. The results demonstrated that the DNA-based biosensor is suitable for the rapid assess of TAC in beverages.

Electroanalytical study of the pesticide ethiofencarb

A detailed study of voltammetric behavior of ethiofencarb (ETF) is reported using glassy carbon electrode (GCE) and hanging mercury drop electrode (HMDE). With GCE, it is possible to verify that the oxidative mechanism is irreversible, independent of pH, and the maximum intensity current was observed at +1.20 V vs. AgCl/Ag at pH 1.9. A linear calibration line was obtained from 1.0x10-4 to 8.0x10-4 mol L-1 with SWV method. To complete the electrochemical knowledge of ETF pesticide, the reduction was also explored with HMDE. A well-defined peak was observed at –1.00V vs. AgCl/Ag in a large range of pH with higher signal at pH 7.0. Linearity was obtained in 4.2x10-6 and 9.4x10-6 mol L-1 ETF concentration range. An immediate alkaline hydrolysis of ETF was executed, producing a phenolic compound (2-ethylthiomethylphenol) (EMP), and the electrochemical activity of the product was examined. It was deduced that it is oxidized on GCE at +0.75V vs. AgCl/Ag with a maximum peak intensity current at pH 3.2, but the compound had no reduction activity on HMDE. Using the decrease of potential peak, a flow injection analysis (FIA) system was developed connected to an amperometric detector, enabling the determination of EMP over concentration range of 1.0x10-7 and 1.0x10-5 mol L-1 at a sampling rate of 60 h-1. The results provided by FIA methodology were performed by comparison with results from high-performance liquid chromatography (HPLC) technique and demonstrated good agreement with relative deviations lower than 4%. Recovery trials were performed and the obtained values were between 98 and 104%.

Evaluation of the total antioxidant capacity of flavored water and electrochemical purine damage by sulfate radicals using a purine-based sensor

In this study, a method for the electrochemical quantification of the total antioxidant capacity (TAC) in beverages was developed. The method is based on the oxidative damage to the purine bases, adenine or guanine, that are immobilized on a glassy carbon electrode (GCE) surface. The oxidative lesions on the DNA bases were promoted by the sulfate radical generated by the persulfate/iron(II) system. The presence of antioxidants on the reactive system promoted the protection of the DNA bases immobilized on the GCE by scavenging the sulfate radical. Square-wave voltammetry (SWV) was the electrochemical technique used to perform this study. The efficiencies of five antioxidants (ascorbic acid, gallic acid, caffeic acid, coumaric acid and resveratrol) in scavenging the sulfate radical and, therefore, their ability to protect the purine bases immobilized on the GCE were investigated. These results demonstrated that the purine-based biosensor is suitable for the rapid assessment of the TAC in flavors and flavored water.

Towards a reliable technology for antioxidant capacity and oxidative damage evaluation: Electrochemical (bio)sensors

To counteract and prevent the deleterious effect of free radicals the living organisms have developed complex endogenous and exogenous antioxidant systems. Several analytical methodologies have been proposed in order to quantify antioxidants in food, beverages and biological fluids. This paper revises the electroanalytical approaches developed for the assessment of the total or individual antioxidant capacity. Four electrochemical sensing approaches have been identified, based on the direct electrochemical detection of antioxidant at bare or chemically modified electrodes, and using enzymatic and DNA-based biosensors.

Maltol determination in food by microwave assisted extraction and electrochemical detection

An electrochemical method is proposed for the determination of maltol in food. Microwave-assisted extraction procedures were developed to assist sample pre-treating steps. Experiments carried out in cyclic voltammetry showed an irreversible and adsorption controlled reduction of maltol. A cathodic peak was observed at -1.0 V for a Hanging Mercury Drop Electrode versus an AgCl/Ag (in saturated KCl), and the peak potential was pH independent. Square wave voltammetric procedures were selected to plot calibration curves. These procedures were carried out with the optimum conditions: pH 6.5; frequency 50 Hz; deposition potential 0.6 V; and deposition time 10 s. A linear behaviour was observed within 5.0 × 10-8 and 3.5 × 10-7 M. The proposed method was applied to the analysis of cakes, and results were compared with those obtained by an independent method. The voltammetric procedure was proven suitable for the analysis of cakes and provided environmental and economical advantages, including reduced toxicity and volume of effluents and decreased consumption of reagents.

Reading performance in children with visual function anomalies

Aims - To compare reading performance in children with and without visual function anomalies and identify the influence of abnormal visual function and other variables in reading ability. Methods - A cross-sectional study was carried in 110 children of school age (6-11 years) with Abnormal Visual Function (AVF) and 562 children with Normal Visual Function (NVF). An orthoptic assessment (visual acuity, ocular alignment, near point of convergence and accommodation, stereopsis and vergences) and autorefraction was carried out. Oral reading was analyzed (list of 34 words). Number of errors, accuracy (percentage of success) and reading speed (words per minute - wpm) were used as reading indicators. Sociodemographic information from parents (n=670) and teachers (n=34) was obtained. Results - Children with AVF had a higher number of errors (AVF=3.00 errors; NVF=1.00 errors; p<0.001), a lower accuracy (AVF=91.18%; NVF=97.06%; p<0.001) and reading speed (AVF=24.71 wpm; NVF=27.39 wpm; p=0.007). Reading speed in the 3rd school grade was not statistically different between the two groups (AVF=31.41 wpm; NVF=32.54 wpm; p=0.113). Children with uncorrected hyperopia (p=0.003) and astigmatism (p=0.019) had worst reading performance. Children in 2nd, 3rd, or 4th grades presented a lower risk of having reading impairment when compared with the 1st grade. Conclusion - Children with AVF had reading impairment in the first school grade. It seems that reading abilities have a wide variation and this disparity lessens in older children. The slow reading characteristics of the children with AVF are similar to dyslexic children, which suggest the need for an eye evaluation before classifying the children as dyslexic.

Preparação para a performance instrumental: problemáticas e estratégias: relatório de estágio

Resumo I (Prática Pedagógica) - Nesta seção do relatório de estágio pretende-se caraterizar e apresentar todos os elementos referentes à prática pedagógica, que fizeram parte do estágio do ensino especializado da música, realizado na Escola de Música do Orfeão de Leiria no ano letivo de 2013/2014. De uma forma geral, o relatório de estágio pretende colocar em evidência aspetos pedagógicos como metodologias de ensino, questões motivacionais, estilos de aprendizagem, entre outros. Durante um ano letivo completo foram analisados, com especial atenção, três alunos que foram envolvidos no estágio, construindo e modelando os seus processos de aprendizagem. Para cada um deles foi realizado, ao longo do ano letivo, 30 planos de aula, uma planificação anual e três gravações vídeo/áudio em contexto de aula. Não foi uma tarefa nada fácil de realizar, mas que trouxe inúmeros conhecimentos não só de caráter pedagógico mas também de caráter pessoal. A parte inicial desta seção será dedicada à descrição e caraterização da escola onde foi realizado o estágio, a Escola de Música do Orfeão de Leiria/Conservatório de Artes. Será feita uma pequena abordagem histórica da instituição, bem como do seu projeto educativo, dacomunidade escolar, do seu contexto sociocultural e da classe de saxofone. Será apresentada também uma caraterização dos alunos, segundo vários parâmetros. Posteriormente, serão descritas algumas das práticas educativas desenvolvidas, com os alunos, em contexto de estágio. Para tal, serão utilizados como instrumentos, não só a experiência ativa do docente/estagiário, mas também todas as gravações, planos de aulas e planificações anuais, realizados em contexto de estágio do ensino especializado. Por fim, será realizada uma reflexão crítica do desempenho como docente de saxofone no âmbito do estágio e uma conclusão de toda a seção da prática pedagógica.

Electrochemical methods in pesticides control

The state of the art of voltammetric and amperometric methods used in the study and determination of pesticides in crops, food, phytopharmaceutical products, and environmental samples is reviewed. The main structural groups of pesticides, i.e., triazines, organophosphates, organochlorides, nitrocompounds, carbamates, thiocarbamates, sulfonylureas, and bipyridinium compounds are considered with some degradation products. The advantages, drawbacks, and trends in the development of voltammetric and amperometric methods for study and determination of pesticides in these samples are discussed.

Linking entrepreneural orientation to export performance: the role of intangible resources and dynamic capabilities

Understanding the determinants of international performance, and in particular, export performance is key for the success of international companies. Research in this area focuses mainly on how resources and capabilities allow companies to gain competitive advantage and superior performance in external markets. Building on the Resource-Based View (RBV) and the Dynamic Capabilities Approach (DCA), this study aims at analysing the effect of intangible resources and capabilities on export performance. Specifically, this study focuses on the proposition that entrepreneurial orientation potentiates the attraction of intangible resources, namely relational and informational resources. Moreover, we propose that these resources impact export performance both directly and indirectly through dynamic capabilities.

Processos cognitivos na performance musical

Existem, actualmente, facilidades e técnicas sem precedentes tendo como fim medir a interpretação musical: medição directa do instrumento, de gravações digitalizadas, medição de imagens vídeo de todo o corpo na interpretação ou só das mãos, medição das características espectrais da música interpretada, informação através de entrevistas com intérpretes e improvisadores, com grupos musicais, informação sobre o estudo do instrumento. Nunca até hoje houve tanto e tão detalhado conhecimento dos processos e manifestações da interpretação musical. Mas o que podem mostrar todas estas medições? Que questões colocam? Que características e que tipos de interpretação foram ignorados? Enfim, o que se aprendeu? E porque tem sido a interpretação musical alvo destas investigações? Este artigo considera e ilustra algumas das diferentes perspectivas de aproximação à interpretação musical, as questões que estes estudos levantam, e discute os sucessos, os fracassos e o futuro deste tipo de investigação.