1,720,955 research outputs found
Innovative LC-MS Approaches for PFAS Detection and Quantification.
Get PDFPer- and polyfluoroalkyl substances (PFAS) comprise a large group of synthetics perfluorinated aliphatic compounds, with over 3,000 known variations. Often referred to as "forever chemicals," these substances are recognized for their exceptional persistence in the environment. They are categorized as contaminants of concern (CECs) and are frequently produced as byproducts in various industrial processes, raising potential environmental and health concerns. Traditional analytical methods often fall short in addressing the unique challenges posed by PFAS due to their complex chemistry, wide variety, and low concentrations typically encountered in environmental samples. Moreover, the growing regulatory scrutiny surrounding PFAS compounds highlights the urgency for advanced detection methodologies. Regulatory agencies and environmental organizations are increasingly setting stringent limits on PFAS levels, necessitating analytical approaches that can reliably detect low concentrations, often in parts per trillion (ppt).
The first part of the dissertation presents the optimization of an advanced method utilizing UHPLC coupled with LEI-NCI-MS for the analysis of PFAS. The adaptability of the LEI interface is highlighted, effectively facilitating the NCI process of the target compounds after chromatographic separation. The investigation examines NCI fragmentations and proposes a series of fragmentation pathways that clarify the mechanisms governing the NCI ionization of PFAS, as well as the processes occurring during ionization. The use of ACN as the sole reagent gas enhances these findings. Through the optimization of the UHPLC-LEI-NCI-MS approach, this research contributes to the understanding of PFAS analysis, focusing on the interactions that occur during NCI ionization. For all samples analyzed, corresponding methyl esters were formed, which can be considered specific ions for PFAS detection and identification.
In the second part, preliminary studies investigate the adsorption and desorption mechanisms associated with ion-exchange extraction phases for 18 per- and polyfluoroalkyl substances (PFAS). The solid-phase microextraction (SPME) device equipped with blade geometry coated in HLB-WAX/PAN exhibited superior extraction efficiency for most of the analyzed compounds. However, non-polar PFAS demonstrated reduced extraction rates, attributed to their hydrophobic properties leading to significant adsorption onto sample container surfaces, which interferes with extraction efficiency. Various desorption parameters were optimized to enhance analysis effectiveness. The determination of the extraction time profile indicated that 30 minutes is optimal for effective PFAS extraction, ensuring adequate quantity extraction and improving throughput for environmental analytical applications. The pre-experiment calibration curve achieved a detection limit of 1 ppt for MOI-MS.Per- and polyfluoroalkyl substances (PFAS) comprise a large group of synthetics perfluorinated aliphatic compounds, with over 3,000 known variations. Often referred to as "forever chemicals," these substances are recognized for their exceptional persistence in the environment. They are categorized as contaminants of concern (CECs) and are frequently produced as byproducts in various industrial processes, raising potential environmental and health concerns. Traditional analytical methods often fall short in addressing the unique challenges posed by PFAS due to their complex chemistry, wide variety, and low concentrations typically encountered in environmental samples. Moreover, the growing regulatory scrutiny surrounding PFAS compounds highlights the urgency for advanced detection methodologies. Regulatory agencies and environmental organizations are increasingly setting stringent limits on PFAS levels, necessitating analytical approaches that can reliably detect low concentrations, often in parts per trillion (ppt).
The first part of the dissertation presents the optimization of an advanced method utilizing UHPLC coupled with LEI-NCI-MS for the analysis of PFAS. The adaptability of the LEI interface is highlighted, effectively facilitating the NCI process of the target compounds after chromatographic separation. The investigation examines NCI fragmentations and proposes a series of fragmentation pathways that clarify the mechanisms governing the NCI ionization of PFAS, as well as the processes occurring during ionization. The use of ACN as the sole reagent gas enhances these findings. Through the optimization of the UHPLC-LEI-NCI-MS approach, this research contributes to the understanding of PFAS analysis, focusing on the interactions that occur during NCI ionization. For all samples analyzed, corresponding methyl esters were formed, which can be considered specific ions for PFAS detection and identification.
In the second part, preliminary studies investigate the adsorption and desorption mechanisms associated with ion-exchange extraction phases for 18 per- and polyfluoroalkyl substances (PFAS). The solid-phase microextraction (SPME) device equipped with blade geometry coated in HLB-WAX/PAN exhibited superior extraction efficiency for most of the analyzed compounds. However, non-polar PFAS demonstrated reduced extraction rates, attributed to their hydrophobic properties leading to significant adsorption onto sample container surfaces, which interferes with extraction efficiency. Various desorption parameters were optimized to enhance analysis effectiveness. The determination of the extraction time profile indicated that 30 minutes is optimal for effective PFAS extraction, ensuring adequate quantity extraction and improving throughput for environmental analytical applications. The pre-experiment calibration curve achieved a detection limit of 1 ppt for MOI-MS
High-Throughput Screening of Polyfluoroalkyl Substances Using Solid-Phase Microextraction Coupled to Microfluidic Open Interface-Mass Spectrometry
No full text: Efficient and sustainable methods for large-scale PFAS monitoring are critical for addressing environmental and public health challenges. This work presents a high-throughput sample preparation system capable of processing up to 48 samples simultaneously using solid-phase microextraction (SPME) and was directly coupled with mass spectrometry (MS) via an automated microfluidic open interface (MOI), bypassing the need for chromatographic separation. The SPME-MOI-MS approach achieves sensitive detection of 18 PFAS in drinking water, with limits of detection (LODs) between 1 and 10 pg/mL, using just 1.5 mL of sample and an average analysis time of 2.8 min per sample. The SPME blades, employed to enhance sensitivity in place of standard SPME fibers, incorporate a matrix-compatible coating material that enables effective PFAS screening in water as well as complex matrices including blood, beer, and beef. In addition, significantly low recovery and reproducibility of nonpolar PFAS in water analysis have been found and studied, indicating that using a glass container and adding a small percentage of acetonitrile can address this issue
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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