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Gli isotopi per la tracciabilità geografica dei cibi e per applicazioni ambientali: strategie di sviluppo dei metodi
No full textLe misure di rapporto isotopico hanno conosciuto un notevole sviluppo dalla fine del XX secolo a oggi e sono state utilizzate nei più diversi contesti scientifici ed applicativi. Tra questi, il monitoraggio dell’evoluzione di prodotti e processi all’interno di cicli produttivi o di ecosistemi trova applicazioni particolarmente interessanti. Il dato di rapporto isotopico, da un lato può fungere da indicatore primario di riferibilità lungo un’intera filiera produttiva (caso del 87Sr/86Sr) mentre dall’altro, attraverso le piccole variazioni delle abbondanze isotopiche relative prodotte dai meccanismi di frazionamento, può fornire utili correlazioni in merito alle trasformazioni subite dall’elemento in questione (caso del δxxxHg).
Condizione necessaria e sufficiente per traguardare questi obiettivi è compiere misure di rapporto isotopico con elevate accuratezza e precisone, sia in termini di ripetibilità che di riproducibilità. La spettrometria di massa con sistema di ionizzazione mediante plasma accoppiato induttivamente e rilevazione a multicollettore, MC-ICP/MS, offre notevoli vantaggi rispetto alle più tradizionali tecniche a termoionizzazione, TIMS, quali l’alta produttività unita alla possibilità di determinare un maggior numero di elementi in virtù della elevata energia di ionizzazione del plasma ad Argon. Tuttavia, tale tecnica introduce una significativa discriminazione di massa strumentale sulle misure – instrumental mass bias – unitamente ad un drift del segnale nel tempo. Una efficace strategia di correzione del dato grezzo risulta dunque cruciale per ottenere misure accurate. Inoltre, le condizioni di misura devono essere attentamente ottimizzate per assicurare una buona precisione interna della determinazione stessa.
Il lavoro di tesi è incentrato su due case-study. Il primo ha riguardato l’ottimizzazione delle condizioni strumentali e di correzione del mass bias per la determinazione di rapporti isotopici del mercurio (Hg), su campioni di sedimenti e di materiali biologici. Questo studio ha rivelato una certa trasmissione della firma isotopica propria delle fonti dell’elemento, oltre a fenomeni di frazionamento sia massa-dipendenti (MDF) che massa-indipendenti (MIF) correlabili alle trasformazioni subite dal mercurio nell’ambiente.
Il secondo riguarda la determinazione dei rapporti isotopici dello stronzio, per uno studio pilota di tracciabilità geografica della Ciliegia di Vignola IGP. In questo studio, il mass bias strumentale è stato corretto utilizzando uno standard esterno di zirconio, permettendo di determinare sia il rapporto radiogenico 87Sr/86Sr, sia il rapporto tra gli isotopi stabili 88Sr/86Sr. I risultati preliminari confermano l’efficacia del rapporto 87Sr/86Sr radiogenico per la tracciabilità dal terreno di coltivazione dei ciliegi, ai tralci e ai frutti corrispondenti. Inoltre, sembrano verificarsi anche frazionamenti degli isotopi stabili dello stronzio, rivelati dalla differenza del rapporto 88Sr/86Sr tra terreno e tralci, mentre non si verificano frazionamenti significativi tra tralci e frutti.Isotopic ratio measurements have notably developed since the end of the XX century to date and have been used in the most different scientific contexts. Among those, monitoring the evolution of products and processes within a production cycle or in the environment finds particularly interesting applications.
The isotopic ratio datum, in fact, can act as primary traceability indicator along an entire production chain (e.g. 87Sr/86Sr). On the other hand, the small variations of isotope ratios determined on matrixes linked to each other identify the fractionation phenomena, which can be linked to the transformations that the considered element undergoes to in the environment (e.g. δxxxHg).
Necessary and sufficient condition to reach these goals is determining isotopic ratios with high precision and accuracy. The mass spectrometry by inductively-coulped-plasma ionization and multicollector detection, MC-ICP/MS, offers considerable advantages with respect to the more traditional thermal ionization mass spectrometry, TIMS, such as high throughput and ability to determinate a larger number of elements thanks to the high ionization energy of the Argon plasma. However, this technique introduces a significant instrumental mass bias on measurements, together with drift phenomena in time.
Effective correction strategies of raw data are thus critical for obtaining accurate measurements. Furthermore, measurement conditions have to be carefully optimized, to ensure a good internal precision of determinations.
Two case studies have been considered in this thesis work. The first one was about the optimization of the instrumental settings and of the mass bias correction for mercury (Hg) isotope ratio measurements on sediment and biological samples. This study revealed the isotopic signatures of the metal are transmitted to some degree into the environment, as well as mass dependent fractionation (MDF) and mass independent fractionation (MIF) phenomena possibly correlated to the mercury transformations occurred in the environment.
The other case study dealt with measurements of strontium isotope ratios for a pilot study about geographic traceability of Vignola Cherry PGI. In this study, instrumental mass bias was corrected by an external zirconium standard, allowing the determination of both the radiogenic ratio 87Sr/86Sr and the ratio between stable isotopes 88Sr/86Sr. Preliminary results confirm 88Sr/86Sr ratio is effective for the traceability from farming soils to the corresponding cherry tree branches and fruits. Furthermore, 88Sr/86Sr ratios differences point out that stable isotope fractionations seem to occur between soil and branches, whereas no significant fractionations take place within branches and fruits
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
MERCURY ISOTOPES DETERMINATIONS IN ENVIRONMENTAL SAMPLES BY MULTICOLLECTOR ICP/MS
No full textMercury isotopes can be an effective tool to investigate about the biogeochemical cycle of Hg, in order to
distinguish among different sources and prevent its well-known pollution in environment and food webs.
In this work, we set up a method for Hg isotopic ratio determination by multicollector ICP-MS
spectrometry by using a cold vapour generator system (CVG). Basically, the system permits to get
measures independent from any matrix effects achieving high precisions and sensitivities. The method
was optimized by Design of Experiment (DoE) technique to minimize inner uncertainty on isotopic
ratios. Instrumental mass bias on measures was accounted by simultaneously monitoring 205Tl/203Tl from
the isotopic SRM NIST 997 and applying the correction algorithm proposed by Yang and Sturgeon.
The method repeatability and reproducibility were evaluated for a two years period on a large data set
built by measuring the NIST 3133 standard solution with an Hg concentration of 20 ng g-1 for more than
500 times. Hg isotope ratios (expressed as mean ± 2 standard deviations), are comparable with those of
others works for all the monitored species, namely 199Hg/198Hg = 1.6881 ± 0.0006, 200Hg/198Hg = 2.3061
± 0.0011, 201Hg/198Hg = 1.3139 ± 0.0014 and 202Hg/198Hg = 2.9635 ± 0.0014.
Precisions and sensitivities of the method are fit for purpose to investigate fractionation phenomena, mass
dependent (MDF) and mass independent (MIF), for Hg that might occur during the uptake processes of
the element and its derivatives in living organisms
Tracing mercury pathways in Augusta Bay (southern Italy) by total concentration and isotope determination
No full textThe mercury (Hg) pollution of sediments is the main carrier of Hg for the biota and,
subsequently, for the local fish consumers in Augusta Bay area (SE Sicily, Italy), a coastal marine
system affected by relevant sewage from an important chlor-alkali factory. This relationship was
revealed by the determination of Mass Dependent (MDF) and Mass Independent Fractionation (MIF) of
Hg isotopes in sediment, fish and human hair samples. Sediments showed MDF but no MIF, while fish
showed MIF, possibly due to photochemical reduction in the water column and depending on the
feeding habitat of the species. Benthic and demersal fish exhibited MDF similar to that of sediments in
which anthropogenic Hg was deposited, while pelagic organisms evidenced higher MDF and MIF due to
photoreduction. Human hair showed high values of δ202Hg (offset of +2.2‰ with respect to the
consumed fish) and Δ199Hg, both associated to fish consumption
DoE optimization of a mercury isotope ratio determination method for environmental studies
No full textBy using the experimental design (DoE) technique, we optimized an analytical method for the determination of mercury isotope ratios by means of cold-vapor multicollector ICP/MS (CV-MC-ICP/MS) to provide absolute Hg isotopic ratio measurements with a suitable internal precision. By running 32 experiments, the influence of mercury and thallium internal standard concentrations, total measuring time and sample flow rate was evaluated. Method was optimized varying Hg concentration between 2 and 20 ng g-1. The model finds out some correlations within the parameters affect the measurements precision and predicts suitable sample measurement precisions for Hg concentrations from 5 ng g-1 Hg upwards.
The method was successfully applied to samples of Manila clams (Ruditapes Philippinarum) coming from the Marano and Grado lagoon (NE Italy), a coastal environment affected by long term mercury contamination mainly due to mining activity. Results show different extents of both mass dependent fractionation (MDF) and mass independent fractionation (MIF) phenomena in clams according to their size and sampling sites in the lagoon. The method is fit for determinations on real samples, allowing for the use of Hg isotopic ratios to study mercury biogeochemical cycles in complex ecosystems
Mercury isotopes to explore sources and fate of Hg in the environment: the case study of the Augusta Bay (southern Italy)
No full textThe Augusta Bay is a nearly closed marine basin located on the southeastern coast of Sicily (southern Italy) which has suffered, since the early 60s, the effect of the uncontrolled chemical discharge of Hg from the most important chlor-alkali plant in Italy (Le Donne and Ciafani, 2008), resulting in high Hg concentrations in sediments, seawater, atmosphere and fishes (Bagnato et al., 2013; Bonsignore et al., 2013; Sprovieri et al., 2001; Ficco et al., 2009; ICRAM, 2005; Ausili et al., 2008; Environ International Team, 2008; Di Leonardo et al., 2007, 2008). For the first time, here we report the results obtained by the measurements of mercury isotopes in sediments, fish muscles and human hair of resident populations, in order to trace sources of Hg and processes driving the biogeochemical cycle of this metal in the environment. Actually, Hg stable isotopes demonstrated an excellent tool for identifying sources and transformation processes of this element in different environmental compartments. Specifically, a positive relationship (r2=0.94; slope: 1.07±0.01) was found between Δ201Hg and Δ199Hg (MIF) for all the environmental matrices coming from the Augusta Bay. This primarily suggests the crucial link between the main Hg source in the Augusta Bay (sediment) and the final receptor (the man) related to fish consumption. Sediments display MIF (expressed as Δ201Hg and Δ199Hg) close to zero and negative MDF (expressed as δ202Hg) that we consider biologically mediated MeHg production. The lower δ202Hg values recorded in the southern area of the basin demonstrated the higher microbial activity occurred just in the zone with the highest mercury concentration in sediments. Furthermore, MIF fractionations in fishes plot on a single line (r2=0.84; slope 1.00±0.03) clearly testifying photochemical reduction of Hg (II) prior of the intake in the marine food web. Moreover, Hg fractionates according to fish ecology with MIF and MDF higher in pelagic fishes and lower ratios in demersal and benthic species. This observation suggests crucial effects of Hg(II) photoreduction processes in surface waters and relevant effects of microbial methylation in the deeper part of the basin. Finally, hair samples show a positive relationship on the base of Δ201Hg and Δ199Hg comparison (r2= 0.93; slope 1.00±0.14) and that we ascribe to the effects of photoreduction of Hg(II) in presence of organic substances. The role of sediments as primary source of Hg for the marine biotic compartment is testified by the overlapping δ202Hg values in fishes and sediments, while the 2‰ difference in δ202Hg values between fishes and hair samples appears consistent with a metabolic fractionation (Laffont et al., 2009)
Application of strontium isotopic analysis to the promotion of the Vignola sweet cherry PGI
Full text linkThe perceived quality of a food commodity may critically depend on the food origin, when regional traditions about the same food production are well-known [1]. This is certainly the case of Vignola Sweet Cherry, which is covered by the Protected Geographical Indication (PGI). The development of a territoriality model for Vignola Sweet Cherry PGI by means of analytical indicators hence represent a very intriguing task, useful for the promotion of the product itself.
In the framework of the pilot project “Ciliegia-UNIMORE2014”, we have assessed the effectiveness of the isotope ratio 87Sr/86Sr as direct traceability indicator, since this indicator have already provided excellent results in similar studies. [2].
Thanks to the collaboration of single producers and to the Association of sweet cherry, plum and typical fruit of Vignola, we have monitored the 87Sr/86Sr ratio in soils, branches and sweet cherry fruits of 3 producing fields, as well as in 100 fruit samples belonging to 20 different cultivars and coming from ten municipalities of the region of production. For a more complete characterization of the cherries, the concentration of 10 metals (major and trace constituents) and the polyphenols content have been determined
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
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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