1,720,960 research outputs found
Investigation of interfering species in phytodrug analysis using an inhibition tyrosinase enzyme electrode working both in water and in organic solvent
No full textIn recent years several inhibition biosensors have been proposed for the analysis of aqueous solutions of phytodrugs. We recently built an inhibition OPEE (organic phase enzyme electrode) based on the inhibition of tyrosinase for the analysis of triazine, carbamate, and organophosphate pesticides operating in water-saturated chloroform. It was possible to determine the concentration of these pesticides contained in lipophilic or aqueous samples by relating it to the inhibiting action measured directly in water, or in water-saturated chloroform, after using the same solvent to extract the pesticides themselves. In the present investigation, attention was focused above all on two points of particular interest: on the study of potential interferents, i.e., of other inhibitors of the tyrosinase enzyme consisting above all, when operating in aqueous solution, of different heavy metal ions or several carboxylic acids, such as cinnamic, sorbic, or benzoic acids, which can apparently interfere in inhibition analysis of pesticides in aqueous matrixes; in the second place, on a detailed comparison of the results of the analysis of triazine, organophosphate, and carbamate pesticides in the presence of the above-mentioned interferents operating both in aqueous solution and in water-saturated chloroform
Carbamate, triazinic and benzotriazinic pesticide analysis using an inhibition organic phase enzyme sensor
No full textTyrosinase inhibition organic phase biosensor for triazinic and benzotriazinic pesticide analysis (part two)
No full textSeveral triazine pesticides, such as atrazine, are much more soluble in several organic solvents, such as chloroform, than in water. Our recent research was aimed at analyzing this class of pesticides using tyrosinase OPEE (organic phase enzyme electrodes), exploiting their inhibiting action on the tyrosinase enzyme when operating in water-saturated chloroform medium. In this work we studied the response of a tyrosinase inhibition enzyme sensor to several triazinic (simazine, propazine, terbuthylazine) and benzotriazinic (azinphos-ethyl and azinphos-methyl) pesticides (LOD=0.5x10(-9) mol l(-1)). Recovery trials were also performed in vegetal matrixes (corn, barley, lentils). Lastly, the effect of the solvent (chloroform or water) on the inhibition process was investigated via Hill's equation and the diffusion of analyte from the solvent to the enzyme membrane
Reliable new immunosensor for atrazine pesticide analysis
No full textThe aim of the present research was to develop a highly selective and sensitive amperometric immunosensor for atrazine based on a "competition" assay procedure. An immunosensor device for the determination of triazinic pesticides based on two different competition procedures is therefore described. The immunosensor developed uses an amperometric electrode for hydrogen peroxide as transducer and the peroxidase enzyme as marker. The results demonstrate the full validity of this immunosensor method which was optimized by comparing two different "competition" operating procedures. The results obtained using the new immunosensor were then compared with those found using an inhibition OPEE (Organic Phase Enzyme Electrode) for triazinic pesticide detection, which showed no selectivity toward different classes of triazinic, carbamate or organophosphate pesticides. The immunosensor developed displayed on the contrary an appreciable selectivity both toward different classes of pesticides and toward triazinic or benzotriazinic products. In addition, the K(aff) value was evaluated. Lastly, the immunosensor was also used to test triazinic pesticide recovery from common real matrices such as milk and vegetal samples, obtaining good recoveries. (C) 2011 Elsevier B.V. All rights reserved
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
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