1,720,968 research outputs found
Compound-specific carbon and hydrogen isotope analysis of volatile organic compounds using headspace solid-phase microextraction
No full textNatural flavouring materials are in high demand, and a premium price is paid for all-natural flavourings, making them vulnerable to fraud. At present, compound-specific isotope analysis (CSIA) is perhaps the most sophisticated tool for determining flavour authenticity. Despite promising results, the method is not widely used, and the results are limited to the most common volatile organic compounds (VOCs). This paper describes a robust protocol for on-line measurements of δ13C and δ2H using HS-SPME coupled with GC-C-IRMS and GC-HTC-IRMS for common fruit VOCs. To achieve reproducible and accurate results, a combination of a peak size/linearity correction with drift correction were used. Finally, the results were normalised by multiple point linear regression using the known and measured values of reference materials. Special care was taken to avoid irreproducible isotopic fractionation and the effects of equilibration, adsorption, desorption times and temperatures on δ13C or δ2H values were examined. Method validation was performed, and the average combined measurement uncertainty (MU) was 0.42‰. All the δ13CVPDB values were below ±3*MU, regardless of analytical conditions. In contrast, for δ2HVSMOW-SLAP values, only low temperature (30 °C) with equilibration time (15 min) and shorter adsorption time (between 10 and 20 min) can produce an isotopic difference of <10‰. Therefore, method optimisation can minimise MU, and data normalisation and method validation are essential for obtaining meaningful data for use in flavour authenticity studie
Using stable isotope databases for authenticity assessment of commercial flavoured products
No full textGas Chromatography Combustion Isotope Ratio Mass Spectrometry for improving the detection of authenticity of grape must
Full text linkSince ancient times, grape must and wine have been considered one of the most sophisticated matrices and, in the last few years, the continuous rise in volumes and prices of grapes and wine has encouraged fraud and adulteration in the oenological field. One of the most common adulterations is sugar addition to grape must in the form of cane or beet sugar or syrup coming from vegetable sources, such as cereals or fruits. Since 1990, the International Organisation of Vine and Wine (OIV) has issued specific official isotopic methods to fight against this practice, but they are not always effective. With the aim to develop a new method able to identify sugar addition, we compared the δ13C value of sugar extracted from grape must analyzed by elemental analyzer/isotope ratio mass spectrometry (EA-IRMS) to the δ13C value of proline analyzed by gas chromatography-combustion isotope ratio mass spectrometry (GC–C–IRMS), after extraction and derivatization. δ13C and δ15N of proline have also been tested as potential geographical markers. In addition, the carbon isotopic composition of two characteristic grape must sugars (myo- and scyllo-inositols) was measured by GC–C–IRMS, after derivatization, to identify the illegal correction of their concentration. On the basis of the obtained results we can conclude that the compound-specific isotope analysis represents a novel analytical tool to support and improve certification and control procedure
C and H stable isotope ratio analysis using solid-phase microextraction and gas chromatography-isotope ratio mass spectrometry for vanillin authentication
No full textIt is possible to distinguish precious vanillin from Vanilla species (planifolia or tahitensis) from much less expensive synthetic and nature-identical vanillin on the basis of the stable isotope ratios of H and C ( 2 H/ 1 H, 13 C/ 12 C). Analysis is usually performed using GC-IRMS (Gas Chromatography - Isotope Ratio Mass Spectrometry) after solvent extraction of vanillin from the sample. Recently, head-space solid-phase microextraction (HS-SPME) has been proposed as an alternative for determining 13 C/ 12 C. The aim of this study was to develop a method to analyse 2 H/ 1 H in vanillin using SPME-GC-IRMS for the first time, by testing different operating conditions and comparing the results with those obtained after solvent extraction. The ultimate scope was to develop a quick, robust and effective method to measure 2 H/ 1 H and 13 C/ 12 C in vanillin to assess the authenticity of labelling. Almost 50 authentic samples from vanilla pods, nature-identical (ex) and synthetic vanillin and 4 commercial food products were taken into account. All the samples were subjected to HS-SPME-GC-IRMS analysis and most of them to GC-IRMS analysis after solvent extraction of vanillin. The SPME method developed for 2 H/ 1 H analysis guarantees the absence of isotopic fractionation, repeatability and reproducibility standard deviation of below 7‰ and savings in terms of time (from 30 to 5 min) and solvent. HS-SPME GC-IRMS analysis of δ 2 H and δ 13 C can be proposed as a rapid and robust method to discriminate different types of vanillin and assess the authenticity of natural vanillin, also contained in food matrice
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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