1,721,019 research outputs found
Accurate area determination of a solid gold electrode coupled with anodic stripping voltammetry for reliable measurements of mercury content in foodstuffs
Full text linkMercury is one of the most toxic elements even at ultratrace levels. Fish accumulates substantial concentrations of this metal in its tissues becoming the primary source of mercury in food chain for humans. For this reason, it is important to develop reliable methods for its determination. Electrochemistry offers attractive routine analysis capabilities, with low-cost instrumentation and applicability to in situ measurements. In particular, anodic stripping voltammetry (ASV), in specific conditions, has the characteristics to become a primary method of measurement, where all the variables are completely understood and traceable to International System of Units (SI).
An effective determination of the available electrode area is the first factor to investigate in these measurements. The area of a solid gold electrode (SGE) was determined with two voltammetric techniques: one consists of cyclic voltage ramps at different scan rates, referred to the Randles-Sevcik equation; the other consists of voltage sweeps at different electrode rotation rates, based on the Levich equation. In both cases, a diffusion controlled process is developed. The redox system ferrocene/ferrocenium was chosen for its well-known reversible process of diffusion-controlled single electron transfer. Acetonitrile and tetrabutylammonium esafluorophosphate were used as solvent and supporting electrolyte respectively. SGE, Ag/AgCl/KCl and graphite wire configuration was adopted.
The estimated areas were compared with that obtained by the elaboration of electrode images taken with a scanning electron microscopy.
ASV coupled with SGE was used firstly for the determination of mercury in tuna certified reference materials (BCR463 and BCR464) and, then, in fresh matrices.
Repeatability, linearity, accuracy and detection limit of the procedure were evaluated.
The medium exchange technique was also tested to reduce matrix effects. Consistent results were obtained.
Aim of this work is the establishment of the traceability to SI units of the ASV in order to apply it to food analysis
Gold nanostructured electrode for the electrochemical determination of mercury in canned tuna
Full text linkThe presence of mercury even at trace and ultratrace level in food constitutes a risk for human health. Therefore, it is important to develop reliable and sensitive analytical methods for the determination of this metal to study how it affects the food chain. Since fish accumulates substantial amounts of mercury in its tissues and constitutes the first source of this element in humans diet, a widespread monitoring of mercury levels in seafood is needed. The applicability of the square wave anodic stripping voltammetry (SW-ASV) for mercury quantification was evaluated adopting a solid gold electrode (SGE) and a nanoparticle-modified glassy carbon electrode (AuNPs-GCE) in certified reference materials and in samples of canned tuna. The achieved results were compared with those obtained by conventional cold vapour atomic absorption spectroscopy (CV-AAS) and by a direct mercury analyser (DMA) based on AAS detection. The evaluation pointed out that SW-ASV is well suited for mercury detection, since a good agreement between spectroscopic and electrochemical approaches was observed. Therefore, SW-ASV can be used with both mentioned electrodes to monitor the mercury content in tuna fish, since the maximum admissible level has been set by European Legislation to 1 mg/kgfw. Furthermore, the SW-ASV coupled with AuNPs-GCE displayed a higher sensitivity than that recorded with SGE: accurate mercury determinations at concentrations lower than 0.1 mg/kg fresh weight (fw) were obtained, showing a limit of quantification comparable to that of DMA. Further advantages of the SW-ASV regard the instrumentation cost that is lower than that required for DMA or CV-AAS, and the presence of this instrumentation in the most of analytical laboratories. Thus, SW-ASV coupled with AuNPs-GCE can be considered suitable for mercury determination even at ultratrace level in tuna fish, and can be adopted as an alternative method by the designated laboratories for routine analysis
Adsorption of heavy metals on vermiculite. Influence of pH and organic ligands
No full textThe sorption behaviour of vermiculite has been studied with respect to cadmium, copper, lead, manganese, nickel, and zinc as a function of pH and in the presence of different ligands. The continuous column method was used in order to evaluate the feasibility to use the clay in wastewater purification systems. The total capacity of vermiculite was found to decrease in the following order: Mn > Ni > Zn > Cd > Cu > Pb. The adsorption of metal ions on vermiculite decreases with decreasing pH and increasing ionic strength. In general, the metal uptake on the clay was hindered by the presence of strong complexing agents in solution and it decreases with increasing of the complexation constants of the ligands with exception of cysteine and tiron. It is necessary, hence, to consider all these factors to effectively predict the uptake efficiency of this sorbent. However, it is possible to conclude that the vermiculite has good potentialities for cost-effective treatments of metal-contaminated wastewaters
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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