1,720,988 research outputs found
Calibration in Thermal Field Flow Fractionation with Polydisperse Standards: Application to Polyolefin characterization
No full textA new procedure for calibrating ThFFF systems by using broad molecular weight standards based on a non-linear least squares fitting of the fractogram to the Molecular Weight Distribution to derive the system calibration parameters is presented and
explored by simulation. This procedure proved robust with respect to noise and it is able to account for detector nonlinearity. The effect of band broadening was evaluated
and it was found that significant bias is observed only for polydispersities lower than 1.3. The method was experimentally validated by using polystyrene in decalin and was then applied to polypropylene under conditions of high temperature ThFFF (Tc = 394 K). It appears that the presented method can be useful in characterising polyolefins polymers for which monodisperse standards are not available
A quick and efficient non-targeted screening test for saffron authentication: Application of chemometrics to gas-chromatographic data
No full textSaffron is one of the most adulterated food products all over the world because of its high market prize. Therefore, a non-targeted approach based on the combination of headspace flash gas-chromatography with flame ionization detection (HS-GC-FID) and chemometrics was tested and evaluated to check adulteration of this spice with two of the principal plant-derived adulterants: turmeric (Curcuma longa L.) and marigold (Calendula officinalis L.). Chemometric models were carried out through both linear discriminant analysis (LDA) and partial least squares discriminant analysis (PLS-DA) from the gas-chromatographic data. These models were also validated by cross validation (CV) and external validation, which were performed by testing both models on pure spices and artificial mixtures capable of simulating adulterations of saffron with the two adulterants examined. These models gave back satisfactory results. Indeed, both models showed functional internal and external prediction ability. The achieved results point out that the method based on a combination of chemometrics with gas-chromatography may provide a rapid and low-cost screening method for the authentication of saffron
Rapid discrimination of Italian Prosecco wines by head-space gas-chromatography basing on the volatile profile as a chemometric fingerprint
Full text linkProsecco wine is one of the most important products of the Italian oenological landscape. Its production is strictly regulated by several disciplinary. Thus, it is important to verify the quality of the final product, to defend the uniqueness of this wine. This work describes a rapid method to discriminate among varieties of Italian Prosecco wine using the volatile-fraction distribution as an untargeted fingerprint. The volatile profile corresponds to gas-chromatograms obtained in head-space mode. Principal components analysis of chromatograms allows discriminating the Prosecco samples depending on geographical origin, cultivation practices, and wine-making technologies. In particular, conventional vs. biological agriculture and manual vs. mechanical harvesting give well-separated clusters when projected on a scores plot. Influence plots allow evaluating which variables are the most effective to describe the differences between oenological classes, which are declared in the label and coded in the disciplinary of origin denomination. The identification of discriminating molecules in the volatile profile is also performed by Kovats indexes. Thus, possible chemical markers for the classification of Italian Prosecco wines are appointed
New polluting metals. Quantification in herbal medicines by voltammetric and spectroscopic analytical methods
Full text linkA new application of voltammetric techniques in stripping mode to the quantitative determination of metals belonging to the platinum group (PGM) in herbal medicines, at the ultra-trace level, is reported. Pd (II), Pt (II) and Rh (III) are determined by means of square-wave adsorption voltammetry (SWAdSV); Os (VIII) and Ru (III) are determined through square-wave voltammetry in catalytic mode (SWCV); Ir (III) is determined through the application of square-wave catalytic voltammetry in adsorption mode (SWAdCSV). In all the applied methods, the voltammetric cell has the conventional setting with three-electrodes, which sees the presence of a suspended mercury-drop electrode (HMDE) or a glassy carbon electrode (GCE) as working electrodes for the determination of Ir (III). The auxiliary electrode was a platinum electrode, and an Ag∣AgCl∣KClsatd. electrode was employed as reference electrode. Validation of the analytical procedure here proposed has been achieved using reference standards: NIST-SRM 1570a (Spinach Leaves) and NIST-SRM 1573a (Tomato Leaves), both added with pure metal standards, obtaining satisfying precision values, better than the limits set for the validation of quantitative methods. Following the verification of the validity of the here presented procedure, commercially available herbal medicines, based on Eucalyptus globulus, Harpagophytum procumbens DC and Taraxacun officinale weber, were analyzed. Standard samples were also analyzed by atomic absorption spectroscopy, in order to have a reference technique for validating the entire procedure
DETERMINATION OF TOXIC METALS IN MARINE BIO-MONITORS BY MULTIVARIATE ANALYSIS OF VOLTAMMETRIC AND SPECTROSCOPIC DATA. APPLICATION TO MUSSELS, ALGAE AND FISHES OF THE NORTHERN ADRIATIC SEA
No full textAn analytical procedure regarding the sequen¬tial voltammetric determination of mercury(II), cop¬per(II), lead(II), cadmium(II) and zinc(II) at trace levels by square wave anodic stripping voltammetry is proposed, and validated by standard reference materials through comparison with spectroscopic analytical methods.
The validated analytical procedure was trans¬ferred and applied to fishes, mussels, and algae as possible biological monitors. Five sampling sites were chosen, located in the Adriatic Sea (Italy) be¬tween the Goro Bay and the Ravenna Lagoon. Multivariate analysis of data by Principal compo¬nents analysis (PCA) and Soft Independent Models of Class Analogy (SIMCA) allowed to explore data: similarities among samples and correlation of varia¬bles was evidenced
Self-organizing maps as a data-driven approach to elucidate the packing motifs of perylene diimide derivatives
Full text linkThe efficient classification or prediction of crystal structures into a small number of families of related structures can be extremely important in the design of materials with specific packing and properties. In this respect, the traditional way to classify the crystal packing of organic semiconductors as herringbone, sandwich-herringbone, and beta- or gamma-sheets by visual inspection has its limitations. Herein, we present the use of a clustering method based on a combination of self-organizing maps and principal component analysis as a data-driven approach to classify different pi-stacking arrangements into families of similar crystal packing. We explored the pi-stacking arrangements within the crystal structures deposited in the Cambridge Structural Database of perylene diimide (PDI) derivatives with different types and positions of the substituents. The structures were characterised by a set of descriptors that were then used for classification. Six different packing families of PDIs were identified and their characteristics are discussed here. Finally, the effects of different substituent types and positions on the resulting packing arrangement are discussed
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
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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