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Kapillärelektrofores kopplad till matrisassisterad laserdesorption-joniserings-masspektrometri med flygtidsanalysator för analys av hindrade aminljusstabilisatorer
No full textPolyolefiner såsom polyeten (PE) och polypropen (PP) utgör en stor andel av den globala plastproduktionen tack vare deras kostnadseffektivitet, kemiska resistens och mekaniska mångsidighet. Däremot är dessa material mycket känsliga för fotooxidation, som främst drivs av ultraviolett (UV) strålning. Detta leder till bildande av fria radikaler, kedjebrott och förlust av strukturell integritet. Hindered Amine Light Stabilizers (HALS) är vanligt förekommande UV-stabilisatorer som motverkar denna nedbrytning genom att fungera som effektiva radikaluppfångare. Trots deras viktiga funktion är analysen av HALS fortsatt utmanande. Detta examensarbete undersöker tillämpningen av kapillärelektrofores (CE) kombinerat med Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Masspektrometri (MALDI-TOF MS) som en metod för separation och detektion av HALS. Sex HALS-substanser tillhandahållna av Norner AS studerades: HALS 2020, 944, 119, 3346, N30 och 62. En omfattande löslighetsanalys med metanol, etanol, isopropanol och acetonitril visade att samtliga HALS var lösliga i alkoholer, med undantag för HALS 62, som i stort sett var olöslig i alla testade lösningsmedel. Trettio olika bakgrundselektrolyter (BGE) designades med kombinationer av ättiksyra/myrsyra, ammoniumsalter och organiska lösningsmedel, både i vattenbaserade och icke-vattenbaserade lösningar. Kapillär zon-elektrofores (CZE) och micellär elektrokinetisk kapillär-kromatografi (MEKC) utvärderades med hjälp av ett Agilent 7100 CE-system. Flera av BGE-systemen möjliggjorde detektion av HALS genom UV-absorbans (framför allt vid 230 nm), där system med alkohol:vatten (60:40) visade de mest lovande resultaten. Trots detta var det svårt att uppnå konsekvent separation på grund av överlappande elektroforetiska mobiliteter (EPM). Dimetylsulfoxid användes som en neutral markör för att utvärdera elektroosmotiska flöden (EOF), vilket förekom i vissa BGE-system men saknades i andra. Kopplingen mellan CE och MALDI-TOF MS möjliggjorde bekräftelse av eluering för HALS 119 och 944. Metoden gav även insikt i molekylviktfördelningar, särskilt för att särskilja mellan monomera och oligomera varianter av HALS 2020, 944 och 119. Vidare forskning bör undersöka användningen av dynamiska kapillärsystem eller bufferttillsatser för att förbättra separationen av HALS med liknande EPM. Att koppla CE till elektrosprayjoniserings-masspektroskopi (ESI-MS) istället för MALDI-TOF MS kan potentiellt leda till högre upplösning, minskad kontaminationsrisk och möjliggöra automatisk provhantering. Sådana förbättringar skulle öka metodens reproducerbarhet och göra den mer lämpad för rutinmässig HALS-analys. Sammanfattningsvis visar CE-MALDI-TOF MS stor potential för kvalitativ detektion av HALS med små provvolymer, men ytterligare arbete krävs för att förbättra separationen. Dessa resultat stödjer utvecklingen av robustare analysmetoder för att spåra stabilisatorer i plast, vilket bidrar till en cirkulär ekonomi.Polyolefins, such as polyethylene (PE) and polypropylene (PP), constitute a major share of global plastic production due to their cost-efficiency, chemical resistance, and mechanical versatility. However, they are highly susceptible to photodegradation, primarily driven by ultraviolet (UV) radiation, which results in the formation of free radicals, chain scission, and a loss of structural integrity. Hindered Amine Light Stabilizers (HALS) are widely used UV stabilizers that mitigate degradation by acting as efficient radical scavengers. Despite their importance, HALS analysis remains analytically challenging. This thesis explores the application of Capillary Electrophoresis (CE) combined with Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry (MALDI-TOF MS) as a method for HALS separation and detection. Six HALS compounds provided by Norner AS were studied: HALS 2020, 944, 119, 3346, N30, and 62. A comprehensive solubility study in methanol, ethanol, isopropanol, and acetonitrile showed that all HALS were soluble in alcohol-based solvents except HALS 62, which remained largely insoluble in all tested solvents. Thirty different background electrolyte (BGE) systems were designed using combinations of acetic/formic acid, ammonium salts, and organic solvents, in both aqueous and non-aqueous formats. Both Capillary Zone Electrophoresis (CZE) and Micellar Electrokinetic Capillary Chromatography (MEKC) were evaluated using an Agilent 7100 CE system. Several BGE systems allowed the detection of HALS via UV absorbance (notably at 230 nm), with alcohol:water (60:40) systems yielding the most promising results. Dimethyl sulfoxide was used as a neutral marker to evaluate electroosmotic flow (EOF), which was present in some BGEs but absent in others. Nevertheless, consistent separation proved difficult due to overlapping electrophoretic mobilities (EPMs). Coupling CE to MALDI-TOF MS enabled the confirmation of HALS elution for HALS 119 and 944, providing insight into molecular weight distributions, particularly when distinguishing between monomeric and oligomeric species in HALS 2020, 944 and 119. In conclusion, CE-MALDI-TOF MS shows strong potential for qualitative HALS detection with minimal sample volume. These findings support the development of more robust analytical methods for tracking stabilizers in plastics, contributing to a circular economy. Further research could explore dynamic capillary coatings or buffer additives to improve the separation of HALS with similar EPM. Coupling CE with electrospray ionization mass spectroscopy (ESI-MS) instead of MALDI-TOF may allow for higher resolution, improved detection, less contamination and automatic sampling
Kapillärelektrofores kopplad till matrisassisterad laserdesorption-joniserings-masspektrometri med flygtidsanalysator för analys av hindrade aminljusstabilisatorer
No full textPolyolefiner såsom polyeten (PE) och polypropen (PP) utgör en stor andel av den globala plastproduktionen tack vare deras kostnadseffektivitet, kemiska resistens och mekaniska mångsidighet. Däremot är dessa material mycket känsliga för fotooxidation, som främst drivs av ultraviolett (UV) strålning. Detta leder till bildande av fria radikaler, kedjebrott och förlust av strukturell integritet. Hindered Amine Light Stabilizers (HALS) är vanligt förekommande UV-stabilisatorer som motverkar denna nedbrytning genom att fungera som effektiva radikaluppfångare. Trots deras viktiga funktion är analysen av HALS fortsatt utmanande. Detta examensarbete undersöker tillämpningen av kapillärelektrofores (CE) kombinerat med Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Masspektrometri (MALDI-TOF MS) som en metod för separation och detektion av HALS. Sex HALS-substanser tillhandahållna av Norner AS studerades: HALS 2020, 944, 119, 3346, N30 och 62. En omfattande löslighetsanalys med metanol, etanol, isopropanol och acetonitril visade att samtliga HALS var lösliga i alkoholer, med undantag för HALS 62, som i stort sett var olöslig i alla testade lösningsmedel. Trettio olika bakgrundselektrolyter (BGE) designades med kombinationer av ättiksyra/myrsyra, ammoniumsalter och organiska lösningsmedel, både i vattenbaserade och icke-vattenbaserade lösningar. Kapillär zon-elektrofores (CZE) och micellär elektrokinetisk kapillär-kromatografi (MEKC) utvärderades med hjälp av ett Agilent 7100 CE-system. Flera av BGE-systemen möjliggjorde detektion av HALS genom UV-absorbans (framför allt vid 230 nm), där system med alkohol:vatten (60:40) visade de mest lovande resultaten. Trots detta var det svårt att uppnå konsekvent separation på grund av överlappande elektroforetiska mobiliteter (EPM). Dimetylsulfoxid användes som en neutral markör för att utvärdera elektroosmotiska flöden (EOF), vilket förekom i vissa BGE-system men saknades i andra. Kopplingen mellan CE och MALDI-TOF MS möjliggjorde bekräftelse av eluering för HALS 119 och 944. Metoden gav även insikt i molekylviktfördelningar, särskilt för att särskilja mellan monomera och oligomera varianter av HALS 2020, 944 och 119. Vidare forskning bör undersöka användningen av dynamiska kapillärsystem eller bufferttillsatser för att förbättra separationen av HALS med liknande EPM. Att koppla CE till elektrosprayjoniserings-masspektroskopi (ESI-MS) istället för MALDI-TOF MS kan potentiellt leda till högre upplösning, minskad kontaminationsrisk och möjliggöra automatisk provhantering. Sådana förbättringar skulle öka metodens reproducerbarhet och göra den mer lämpad för rutinmässig HALS-analys. Sammanfattningsvis visar CE-MALDI-TOF MS stor potential för kvalitativ detektion av HALS med små provvolymer, men ytterligare arbete krävs för att förbättra separationen. Dessa resultat stödjer utvecklingen av robustare analysmetoder för att spåra stabilisatorer i plast, vilket bidrar till en cirkulär ekonomi.Polyolefins, such as polyethylene (PE) and polypropylene (PP), constitute a major share of global plastic production due to their cost-efficiency, chemical resistance, and mechanical versatility. However, they are highly susceptible to photodegradation, primarily driven by ultraviolet (UV) radiation, which results in the formation of free radicals, chain scission, and a loss of structural integrity. Hindered Amine Light Stabilizers (HALS) are widely used UV stabilizers that mitigate degradation by acting as efficient radical scavengers. Despite their importance, HALS analysis remains analytically challenging. This thesis explores the application of Capillary Electrophoresis (CE) combined with Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry (MALDI-TOF MS) as a method for HALS separation and detection. Six HALS compounds provided by Norner AS were studied: HALS 2020, 944, 119, 3346, N30, and 62. A comprehensive solubility study in methanol, ethanol, isopropanol, and acetonitrile showed that all HALS were soluble in alcohol-based solvents except HALS 62, which remained largely insoluble in all tested solvents. Thirty different background electrolyte (BGE) systems were designed using combinations of acetic/formic acid, ammonium salts, and organic solvents, in both aqueous and non-aqueous formats. Both Capillary Zone Electrophoresis (CZE) and Micellar Electrokinetic Capillary Chromatography (MEKC) were evaluated using an Agilent 7100 CE system. Several BGE systems allowed the detection of HALS via UV absorbance (notably at 230 nm), with alcohol:water (60:40) systems yielding the most promising results. Dimethyl sulfoxide was used as a neutral marker to evaluate electroosmotic flow (EOF), which was present in some BGEs but absent in others. Nevertheless, consistent separation proved difficult due to overlapping electrophoretic mobilities (EPMs). Coupling CE to MALDI-TOF MS enabled the confirmation of HALS elution for HALS 119 and 944, providing insight into molecular weight distributions, particularly when distinguishing between monomeric and oligomeric species in HALS 2020, 944 and 119. In conclusion, CE-MALDI-TOF MS shows strong potential for qualitative HALS detection with minimal sample volume. These findings support the development of more robust analytical methods for tracking stabilizers in plastics, contributing to a circular economy. Further research could explore dynamic capillary coatings or buffer additives to improve the separation of HALS with similar EPM. Coupling CE with electrospray ionization mass spectroscopy (ESI-MS) instead of MALDI-TOF may allow for higher resolution, improved detection, less contamination and automatic sampling
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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