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“Desarrollo de una metodología electroanalítica para la determinación de Se(IV) utilizando un electrodo película de bismuto, libre de mercurio”
Get PDFEste trabajo se enfoca en el desarrollo de un método electroanalítico que permita la detección y
cuantificación de selenio (IV) mediante voltamperometría de stripping catódico (CSV) utilizando
un electrodo de carbono vitreo modificado con una película de bismuto (BiFE) ex-situ libre de
mercurio. Se optimizaron los diferentes parámetros experimentales para la obtención de un método
sensible, selectivo y reproducible. Los parámetros experimentales optimizados para la formación
de la película fueron: tampón ácido acético/acetato pH 4,5, potencial y tiempo de depósito -0,8 V
y 300 segundos respectivamente, concentración de Bi(III) 100 mg L-1
. Las mejores condiciones
para la medición de Se(IV) fueron: 50 mmol L-1
de HClO4 , pH ≤ 2,9, potencial y tiempo de
preconcentración de Se(IV) -0,5 V y 60 segundos respectivamente, potencial y tiempo de limpieza
-0,9 V y 3 segundos respectivamente
Los límites de detección y cuantificación obtenidos fueron: LD: 0,143 µg L
-1
y LQ: 0,435 µg L
-1
de Se(IV) en ausencia de AcN y en presencia de AcN se obtuvo, LD: 0,428 µg L
-1
y LQ: 1,297 µg
L
-1
de Se(IV). Se estudió la posible interferencia de tres aniones comunes presentes en muestras de
agua, tres agentes enmascarantes y 34 iones metálicos. Cu(II) fue el mayor interferente, se logró
disminuir la interferencia de Cu(II) mediante la adición de AcN al 50% en la celda electroquímica.
Este método fue validado utilizando dos materiales de referencia certificados (TM-28,4 y TDMA 62,2) y fue aplicado en cuatro muestras reales (agua mineral comercial fortificada en selenio, agua
de pozo de la zona de Batuco (Padre Hurtado), agua del río Loa (Calama) y agua potable del
laboratorio. Este trabajo presenta un método alternativo para la determinación de Se(IV) de forma
rápida, sencilla y económica, con la ventaja de poder eliminar el uso de mercurio en el electrodo
de trabajoThis work focuses on the development of an electroanalytical method that allows the detection and
quantification of selenium (IV) by means of cathodic stripping voltammetry (CSV) using a glassy
carbon electrode modified with an ex-situ bismuth film (BiFE) free of mercury. The different
experimental parameters were optimized to obtain a sensitive, selective, and reproducible method.
The optimized experimental parameters for the formation of the film were: acetic acid/acetate
buffer pH 4.5, potential and deposition time -0.8 V and 300 seconds respectively, Bi(III)
concentration 100 mg L-1. The best conditions for Se(IV) measurement were: 50 mmol L-1 of
HClO4 , pH ≤ 2.9, potential and Se(IV) preconcentration time -0.5 V and 60 seconds respectively,
potential and time cleaning -0.9 V and 3 seconds respectively. The detection and quantification
limits obtained were: LD: 0.143 µg L-1 and LQ: 0.435 µg L-1 of Se(IV) in the absence of AcN
and in the presence of AcN, LD: 0.428 µg L-1 and LQ was obtained: 1.297 µg L-1 of Se(IV). The
possible interference of three common anions presents in water samples, three masking agents and
34 metal ions were studied. Cu(II) was the major interferent, it was possible to reduce the
interference of Cu(II) by adding 50% AcN in the electrochemical cell. This method was validated
using two certified reference materials (TM-28.4 and TDMA-62.2) and was applied to four real
samples (selenium-fortified commercial mineral water, well water from the Batuco area (Padre
Hurtado), from the Loa River (Calama) and drinking water from the laboratory. This work presents
an alternative method for the determination of Se(IV) in a fast, simple, and economic way, with
the advantage of being able to eliminate the use of mercury in the working electrodeVersión original del auto
Determinación de Ga(III) mediante el uso de un electrodo modificado con película de bismuto. Uso de un agente complejante para aumentar la sensibilidad
Get PDFEste seminario tiene como objetivo principal el desarrollo y optimización de una metodología
electroanalítica rápida para la detección y cuantificación de Ga(III), utilizando voltamperometría
de redisolución anódica de onda cuadrada y un electrodo de carbono vítreo modificado con una
película in situ de bismuto y en presencia del agente complejante sulfonado rojo de alizarina s
(ARS), ya que su adición demostró incrementar la sensibilidad del método. La optimización de las
condiciones experimentales se realizó considerando el depósito de la película de bismuto y
acumulación de galio en la base del electrodo de trabajo, definiendo como electrolito soporte una
solución tampón ácido acético/acetato de sodio 34,5 mmol L-1 a pH 4,5, concentración de Bi(III)
2,5 mg L-1, concentración de ARS 1,0 µmol L-1, tiempo y potencial de depósito respectivos de 60
s y -1,2 V. También se realizó un proceso de limpieza sobre el electrodo de trabajo, para asegurar
una menor variabilidad entre medidas, definiendo un tiempo y potencial de limpieza de 15 s y 1,0
V, respectivamente. Obteniendo límites de detección y cuantificación respectivos de 0,182 µg L-1
y 0,551 µg L-1
de Ga, para un rango lineal de concentración de galio desde 1,0 hasta 30,0 µg L-1.
La precisión de este método se expresa mediante una repetibilidad de 7,44%, calculada a partir de
la respuesta analítica de 20 medidas consecutivas y, una reproducibilidad del 8,57%, a partir de 25
mediciones realizadas en distintas oportunidades, manteniendo en ambos estudios las mismas
condiciones experimentales.
Se estudió la posible interferencia de aniones comunes de detectar en muestras reales de agua,
como cloruros, sulfatos y nitratos. En el caso de Cl hubo un aumento en la intensidad de la señal
de galio a una concentración del anión de 10,0 mmol L
-1, mientras que para una misma cantidad de SO4-2 y NO3- se obtuvo una disminución en la respuesta analítica. También se evaluó el efecto
de una serie de iones metálicos, entre los cuales destacan como interferentes relevantes sobre la
intensidad de la señal de galio, V(V), Cr(III), Co(II), Ni(II), Cu(II), Mo(VI), Cd(II)y Pb(II), debido a que bajas proporciones de estos iones aumentaron o redujeron de manera significativa (<10,0%),
la respuesta analítica de una concentración fija de galio. Se realizó un estudio de agentes
enmascarantes CDTA, EDTA y NaF, para disminuir la interferencia de estos metales. De los cuales
se obtuvieron resultados favorables al añadir CDTA y NaF en concentraciones respectivas de 2,5
y 50,0 µmol L-1, para reducir el efecto de Cd(II) y Pb(II) y en cierto grado la interferencia de
Cu(II). Esta adaptación del método desarrollado no modificó significativamente los límites de
detección y cuantificación, pero, disminuyó la selectividad en la detección de Ga (III), además de
ser menos preciso, con una repetibilidad de 18,33% (n=10).
No fue posible validar la metodología con material de referencia certificado TMDA-62,2 (MRC),
al no poder reducir la interferencia de todas las especies metálicas presentes en el MRC. Sin
embargo, su aplicación si fue posible en muestras reales de agua potable (Ñuñoa), agua mineral
purificada, agua de pozo (Padre Hurtado), dopadas con galio. Reduciendo el efecto matriz con el
método de adición de estándar.The main objective of this seminar is developing and optimizing a rapid electroanalytical
methodology for detecting and quantifying Ga(III), using square wave anodic stripping
voltammetry and a glassy carbon electrode modified with an in situ bismuth film and in the
presence of the sulfonate complexing agent alizarin red s (ARS), since its addition was shown to
increase the sensitivity of the method. The optimization of the experimental conditions was
performed considering the deposition of the bismuth film and gallium accumulation at the base of
the working electrode, defining as supporting electrolyte an acetic acid/sodium acetate buffer
solution 34.5 mmol L-1 at pH 4.5, Bi(III) concentration 2.5 mg L-1, ARS concentration 1.0 µmol
L-1, respective deposition time and potential of 60 s and -1.2 V. A cleaning process was also
performed on the working electrode to ensure a lower variability between measurements, defining
a cleaning time and potential of 15 s and 1.0 V, respectively. The respective limits of detection
and quantification were 0.182 µg L
-1 and 0.551 µg L
-1 of Ga, for a linear range of gallium
concentration from 1.0 to 30.0 µg L
-1. The precision of this method is expressed by a repeatability
of 7.44%, calculated from the analytical response of 20 consecutive measurements, and a
reproducibility of 8.57%, from 25 measurements made on different occasions, maintaining the
same experimental conditions in both studies.
The possible interference of anions common to detect in real water samples, such as chlorides,
sulfates and nitrates, was studied. In the case of Cl there was an increase in the intensity of the
gallium signal at an anion concentration of 10.0 mmol L-1, while for the same amount of SO4-2
and NO3- a decrease in the analytical response was obtained. The effect of a series of metal ions was
also evaluated, among which V(V), Cr(III), Co(II), Co(II), Ni(II), Cu(II), Mo(VI), Cd(II) and
Pb(II) stand out as relevant interferents on the gallium signal intensity, since low proportions of
these ions significantly increased or reduced (<10.0%) the analytical response of a fixed gallium
concentration. A study of masking agents CDTA, EDTA and NaF was carried out to reduce the
interference of these metals. Favorable results were obtained by adding CDTA and NaF at
respective concentrations of 2.5 and 50.0 µmol L
-1
, to reduce the effect of Cd(II) and Pb(II) and to
some extent the interference of Cu(II). This adaptation of the developed method did not
significantly modify the detection and quantification limits, but, it decreased the selectivity in the
detection of Ga(III), besides being less precise, with a repeatability of 18.33% (n=10).
It was not possible to validate the methodology with certified reference material TMDA-62,2
(CRM), since it was not possible to reduce the interference of all the metallic species present in
the CRM. However, its application was possible in real samples of drinking water (Ñuñoa),
purified mineral water, well water (Padre Hurtado), doped with gallium. Reducing the matrix
effect with standard addition method.Proyecto PAI Nº 77190012Versión original del auto
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Get PDFWe 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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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