1,721,106 research outputs found
Determination of trace zinc in seawater by coupling solid phase extraction and fluorescence detection in the Lab-On-Valve format
No full textBy virtue of their compactness, long-term stability, minimal reagent consumption and robustness, miniaturized sequential injection instruments are well suited for automation of assays onboard research ships. However, in order to reach the sensitivity and limit of detection required for open-ocean determinations of trace elements, it is necessary to preconcentrate the analyte prior its derivatization and subsequent detection by fluorescence. In this work, a novel method for the determination of dissolved zinc (Zn) at subnanomolar levels in seawater is described. The proposed method combines, for the first time, automated matrix removal, extraction of the target element, and fluorescence detection within a miniaturized flow manifold, based on the Lab-On-Valve (LOV) concept. The key feature of the microfluidic manipulation of the sample is flow programming, designed to pass sample through a mini-column where the target analyte and other complexable cations are retained, while the seawater matrix is washed out. Next, zinc is eluted and merged with a Zn selective fluorescent probe (FluoZin-3) at the confluence point of the LOV central channel using two high-precision stepper motor driven pumps that are operated in concert. Finally, the thus formed Zn complex is transported to the LOV flow cell for selective fluorescence measurement. This work describes the characterization and optimization of the method including Solid Phase Extraction using the Toyopearl AF-Chelate-650M resin, and detailed assay protocol controlled by a commercially available software and instrument. The proposed method features a LOD of 0.02 nM, high precision (<3% at 0.1 and 2 nM Zn levels), an assay cycle of 13 min and a reagent consumption of 150 ?L FluoZin-3 per sample, which makes the method highly suitable for oceanographic shipboard analysis. The accuracy of the method has been validated through the analysis of seawater reference standards and comparison with ICP-MS determinations on seawater samples collected in the upper 1300 m of the subtropical south Indian Ocean. This work confirms that integration of sample pretreatment with optical detection in the LOV format offers a widely applicable approach to trace analysis of seawater
Multilayered particle-packed column: Evaluation and comparison with monolithic and core-shell particle columns for the determination of red azo dyes in Sequential Injection Chromatography
Get PDFA recently presented new type of "multilayered" organic-inorganic hybrid silica particle packed column YMC-Triart C18 (50 mm × 4.6 mm, 5 μm) was used for the development of a sequential injection chromatography method for determination of five azo dyes (Sudan I, Sudan II, Sudan III, Sudan orange G, and para red) in selected food seasonings. The use of a novel sorbent brings attractive features, reduced backpressure, and broader chemical stability together with high separation performance, which are discussed and compared with that of three types of columns typically used in medium-pressure flow chromatography techniques (classic monolithic, narrow monolithic, and core-shell particle columns). The separation was performed in gradient elution mode created by the zone mixing of two mobile phases (acetonitrile/water 90:10, 1.5 mL + acetonitrile/water 100:0, 2.3 mL) at a flow rate of 0.60 mL/min and time of analysis <9.5 min. The spectrophotometric detection wavelengths were set to 400, 480, and 500 nm. The high performance of the developed method with multilayered particle column was well documented and the results indicate a broad capability of sequential injection chromatography.Fil: Chocholouš, Petr. Charles University Hradec Králové; República ChecaFil: Gil, Renato. Universidad de Porto; PortugalFil: Acebal, Carolina Cecilia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; ArgentinaFil: Kubala, Victor. Charles University Hradec Králové; República ChecaFil: Šatínský, Dalibor. Charles University Hradec Králové; República ChecaFil: Solich, Petr. Charles University Hradec Králové; República Chec
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
Application of DV-SIA manifold for determination of thiocyanate ions in human saliva samples
Get PDFAn automated, simple and inexpensive double-valve sequential injection analysis (DV-SIA) spectrophotometic method with online liquid-liquid extraction, for the determination of thiocyanate has been developed. The method has been based on the formation of an ion associate between thiocyanate and Astra Phloxine in acidic medium, and the subsequent extraction with amylacetate. The absorbance of the extracted ion associate was measured at 550 nm. The calibration function was linear in the range 0.05-0.50 mmol L-1 and the regression equation was A = (1.887 ± 0.053) [SCN- mmol L-1] + (0.037 ± 0.014) with a correlation coefficient of 0.995. The precision of the proposed method was evaluated by the relative standard deviation (RSD) values at two concentration levels: 0.20 and 0.50 mmol L-1. The obtained results were 1.0 and 2.8%, respectively, for the intra-day precision, and 4.2 and 3.8%, respectively for the inter-day precision. The calculated detection limit was 0.02 mmol L-1. The developed method has been successfully applied for determining thiocyanate ions in human saliva samples. © 2012 Elsevier B.V. All rights reserved.Fil: Acebal, Carolina Cecilia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; Argentina. Charles University; República ChecaFil: Sklená?ová, Hana. Charles University; República ChecaFil: Skrlíková, Jana. Charles University; República Checa. University of Pavol Jozef Šafárik; República ChecaFil: Srámková, Ivana. Charles University; República ChecaFil: Andruch, Vasil. University of Pavol Jozef Šafárik; República ChecaFil: Balogh, Ioseph S.. College of Nyíregyház; HungríaFil: Solich, Petr. Charles University; República Chec
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
Development of HPLC method for assesment of stability of amorphous compounds
No full textCharles University in Prague Faculty of Pharmacy in Hradec Králové Department of Analytical Chemistry Candidate: Daniela Číhalová Supervisor: Prof. RNDr. Petr Solich, CSc., Prof. Seppo Auriola, MSc. Marko Lehtonen Title of diploma thesis: Development of HPLC method for assessment of stability of amorphous compounds Solid materials can be found in many diverse forms which are distinguishable by different properties. In my thesis, I focus on amorphous solids, their properties, significance, occurrence and, most of all, characterization. The most widely used methods are introduced and described, focusing on their practical use in characterizing polymorphic and amorphous compounds. During the preparation of an amorphous solid, rapid heating and cooling down occurs and therefore degradation can be expected. To prove thermal stability, an HPLC method has been developed and validated for the determination of concentration decrease of an active pharmaceutical ingredient in amorphous state of 8 compounds. The compounds (benzocaine, chlorpropamide, clotrimazole, furosemide, piroxicam, salicylic acid, thiosalicylic acid, and tolbutamide) were determined separately. The method was carried out on a reversed-phase column (1.8µm, 50 × 4.6 mm) maintained at 40řC. The mobile phase was acetonitrile-water containing..
Analýza atorvastatonu metodou kapalinové chromatografie s využitím fluorescenční derivatizace
Get PDF10.2 Determination of atorvastatin by high performance liquid chromatography with fluorescence detection The main aim of this work was to develop a method for determination of atorvastatin by HPLC, which would be sensitive enough to determine plasmatic concentration of atorvastatin (ng/ml). UV-VIS detection is not sensitive enough for this purpose, therefore fluorescence detection was used. Atorvastatin was derived by 4-brommethyl-6,7-dimethoxycoumarin in N,N- dimethylformamide. Potassium carbonate and 18-crown-6-ether were used as catalysts. Optimal conditions for the reaction were determined as follows: 45 minutes, 20řC in dark. The method of purification of sample from undesired substances was not successful. However HPLC conditions were fully optimized, the column-switching technique was not effective enough. Chromatograms were not so selective, and desired level of sensitivity was not reached.10 Abstrakty 10.1 Analýza atorvastatinu metódou kvapalinovej chromatografie s využitím fluorescenčnej derivatizacie Hlavným cieľom tejto práce bolo vyvinúť metódu stanovenia atorvastatinu pomocou HPLC, ktorá by bola dostatočne citlivá na stanovenie plazmatických hladín, teda koncentrácii v jednotkách ng/ml. UV-VIS detekcia nie je dostatočne citlivá na tento účel, preto bola použitá fluorescenčná detekcia. Atorvastatin bol derivatizovaný pomocou 4-bromometyl-6,7-dimetoxykumarínu v prostredí N,N-dimethylformamidu, ako katalyzátory boli použité uhličitan draselný a 18-crown-6- ether. Bola prevedená optimalizácia reakčných podmienok, pričom sa zistilo, že optimálne podmienky sú inkubácia v tme po dobu 45 minút pri teplote 20řC. Metódu vyčistenia vzorky od nežiaducich látok sa však optimalizovať nepodarilo. Technika prepínania kolón nebola s použitými kolónami dostatočne účinná, takže výsledné chromatogramy boli aj napriek maximálnej optimalizácii chromatografických podmienok stále značne znečistené interferujúcimi látkami, a teda požadovaná úroveň citlivosti nebola dosiahnutá.Department of Analytical ChemistryKatedra analytické chemieFarmaceutická fakulta v Hradci KrálovéFaculty of Pharmacy in Hradec Králov
- …
