1,720,997 research outputs found
Determinazione di ritardanti di fiamma bromurati contaminanti matrici acquose mediante LC/APPI-MS/MS
No full textI ritardanti di fiamma sono composti chimici utilizzati come additivi, aggiunti durante o al termine della lavorazione di un materiale, per ritardare la fase iniziale del processo di combustione, per ridurre l’infiammabilità di materiali polimerici nel rispetto delle norme antincendio, per impedire o rallentare lo sviluppo di incendi. La tipologia dei ritardanti di fiamma copre un ampio spettro di composti che soddisfano le più svariate esigenze. Il gruppo dei ritardanti di fiamma a base di bromo comprende diversi composti organobromurati utilizzati per impedire la combustione e/o per ritardare la diffusione delle fiamme in diversi tipi di plastica, prodotti tessili ed altri materiali.
Sono tre i gruppi chimici impiegati più comunemente: i difenileteri polibromurati (PBDE), l’esabromociclododecano (HBCD), usati come additivi, ed i bisfenoli bromurati (in particolare il TBBP-A) più comunemente usati come reagenti data la loro maggiore capacità di legarsi con i polimeri in cui vengono incorporati.
Il problema ambientale dei ritardanti di fiamma nasce negli anni novanta, quando nei sedimenti del Mar Baltico è stato rilevato un aumento sensibile delle concentrazioni di PBB (difenilipolibromurati) e PBDE. Studi successivi condotti in Svezia, hanno dimostrato che tali composti sono persistenti e soggetti a notevole bioaccumulo nella catena alimentare. Infine, la Direttiva 2003/11/CE ha posto limitazioni alla produzione ed utilizzo di questo tipo di composti per le ragioni sinteticamente esposte, sebbene in presenza di caratteristiche di tossicità acuta non preoccupanti.
I metodi analitici finora sviluppati per la determinazione di queste sostanze comprendono l’estrazione e la micro-estrazione in fase solida (SPE e SPME), l’estrazioni liquido-liquido con membrana microporosa (MMLLE) e la mirco-estrazione liquido-liquido (DLLME) utilizzate su campioni liquidi; l’estrazione Soxhlet utilizzata su campioni atmosferici di particolato.
Le tecniche analitiche sin qui utilizzate sono: cromatografia liquida ad alte prestazioni accoppiata a rivelatore ultravioletto (HPLC-VWD), gascromatografia con rivelatore a cattura di elettroni (GC-ECD) e gascromatografia con ionizzazione chimica (CI) o elettronica (EI) e rivelazione mass-spettrometrica (GC-CI–MS, GC-EI–MS, GC-NCI-MS).
Lo scopo di questo lavoro è la messa a punto di un nuovo metodo di conferma, rapido e robusto, basato sulla HPLC APPI*-MS/MS per la determinazione di basse concentrazioni di ritardanti di fiamma polibromurati in campioni di acqua; in tabella I sono riportati i composti investigati, caratteristici della classe
Profilo metabolico urinario di soggetti coinvolti nell’esperimento Mars500 mediante LC-QTOF MS e analisi multivariata multivariata
No full textLiquid chromatography–negative ion atmospheric pressure photoionization tandem mass spectrometry for the determination of brominated flame retardants in environmental water and industrial effluents
No full textWe describe the development of a liquid chromatography with negative-ion atmospheric pressure photoionization tandem mass spectrometric (LC/NI-APPI/MS/MS) method for the simultaneous determination of tetrabromobisphenol A (TBBP-A) and five polybrominated diphenyl ethers (BDE-47, BDE-99, BDE-100, BDE-153 and BDE-154) in water. A mobile phase methanol/acetone/water was used, where acetone acts also as dopant. NI-APPI produced precursor ions corresponding to [M?H]? for TBBP-A, [M?Br+O]?, and [M?2Br+O]? for the BDE congeners studied. Each compound was quantified operating in multiple reaction monitoring mode. Linearity was observed in the range 0.025–10 ng injected for all compounds. Coefficients of determination R2 ranged from0.9934 to 0.9982. BDEswere poorly retained by solid-phase extraction (SPE) from river water and sewage treatment plant effluent, thus liquid–liquid extraction (LLE) by n-hexane should be used for these samples. The recoveries of TBBP-A and PBDEs from tap water (SPE), river water and industrial wastewater (LLE) were in the range of 81–88%, 78–92%, and 43–99%, respectively, with relative standard deviations below 17%. The limits of detection, based on signal-to-noise ratio of 3, ranged from 0.004 to 0.1 ng injected, and method quantification limits were 0.2–3.3 ng L?1 but BDE47 (20.3 ng L?1). Only TBBP-A was found in a treated industrial sewage at 4 ng L?1, while BDE-99 and BDE-100 were detected on suspended solids
Recent developments in matrix solid-phase dispersion extraction
No full textMatrix solid-phase dispersion is a sample preparation strategy widely applied to solid, semisolid or viscous samples, including animal tissues and foods with a high lipidic content. The process consists in blending the matrix onto a solid support, allowing the matrix cell disruption and the subsequent extraction of target analytes by means of a suitable elution solvent. First introduced in 1989, MSPD employment and developments are still growing because of the feasibility and versatility of the process, as evidenced by the several reviews that have been published since nineties. Therefore, the aim of the present review is to provide a general overview and an update of the last developments of MSPD. (C) 2010 Elsevier B.V. All rights reserved
Multidimensional chromatography: An essential tool for proteomics
No full textThe general strategy in proteomic research consists in sample preparation, protein or peptide separation, their identification, and data interpretation. A critical step is certainly protein or peptide separation. Since increasingly complicated biological structures are studied by mass spectrometry (MS), the need for more powerful and highly resolving separation methods is growing. Consequently, multidimensional separation techniques in combination with MS have emerged as a powerful tool for the large-scale proteomic analysis. Until recently, two dimensional gel electrophoresis (2-DE) was the technique most often used for protein separation. The limitations of 2-DE in detecting low abundance, very small or large proteins, basic and membrane/ hydrophobic ones, as well as difficulties with process automation, have forced researchers to look for other methods of protein separation, such as multidimensional liquid chromatography coupled to MS (MDLC-MS) or LC to increase the peak capacity, and thus the resolving power of separation, to better fractionate peptides prior to entering the mass spectrometer. In this chapter, we analyze status and recent developments of the MDLC experiments in their fundamental components. It describes a variety of separation modes that have been employed to achieve protein-level or peptide-level separation, including size exclusion chromatography, ion exchange chromatography, and reversed-phase chromatography. We also discuss the advantages and disadvantages of two different approaches that can be followed for the studies of proteomics: protein-level separation or peptide-level separation. © 2011 by Nova Science Publishers, Inc. 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
Flavonoids: chemical properties and analytical methodologies of identification and quantitation in foods and plants
No full textFlavonoids have been recognised as one of the largest and most widespread groups of plant secondary metabolites, with marked antioxidant properties. The general name flavonoid refers to a class of more than 6500 molecules based upon a 15-carbon skeleton. In this paper a general overview of flavonoids, their classification, structures and analytical methods for their determination is presented
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
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