XII Iberian Meeting of Electrochemistry XVI Meeting of the ...

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XII Iberian Meeting of Electrochemistry & XVI Meeting of the Portuguese Electrochemical Society O B 01 Application of a Membraneless Extraction Module in the Voltammetric Determination of Sulphites in Wine Luís M. Gonçalves, Miriam F. Anunciação, Inês M. Valente, João G. Pacheco, José M. Rodrigues, Aquiles A. Barros Requimte, Departamento de Química e Bioquímica, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre, no. 687, 4169-007 Porto, Portugal luis.goncalves@fc.up.pt In this work, a new methodology for the voltammetric analysis of sulphites in wine is proposed [1]. It makes use of a recently developed membraneless extraction module (MLEM) for the analysis of volatile and semi-volatile compounds [2]. Sulphites are widely used as preservatives in the food industry for their several roles including the prevention of undesirable microbial growth and oxidation processes. Among a whole variety of methodologies proposed for the determination of sulphites in wine, the most used are based on the classical Monier-Williams procedure and the also ancient Ripper method. Nevertheless, voltammetric-based methodologies appear to be the most accurate ones. Square-wave voltammetry (SWV) is very advantageous in the determination of sulphites since there is a direct detection, i.e. it is the SO 2 molecule that is instrumentally measured in the electrode [3]. The major drawback when using voltammetry is the previous analyte extraction step required since wine is such a complex matrix. The extraction process is based on a MLEM that works with the same principles of pervaporation however it does not require a membrane, and therefore does not have the associated problems with its use. The sample is placed inside the module and the volatile compounds evaporate to the headspace. Inside the module there is a suspended small reactor, where a small volume of an acceptor solution is placed. After a period of time, the acceptor solution is collected and analyzed by SWV. The proposed method was validated by comparison to the reference methodology. It showed repeatability (RSD lower than 5%) and linearity (between 20 to 200 mg L -1 ) as well as suitable limit of detection (6 mg L -1 ). Moreover, if needed, these limits can be easily lowered by increasing the time of extraction, which in this case was less than 5 minutes. Acknowledgments: LMG (SFRH/BD/36791/2007) and JGP (SFRH/BD/30279/2006) wish to acknowledge Portuguese Fundação para a Ciência e Tecnologia (F CT) for their PhD studentships. References [1] Gonçalves, L.M.; Anunciação, M.F., Valente, I.M., Pacheco, J.G.; Magalhães, P.J.; Rodrigues, J.A.; Barros, A.A. Collection of Czechoslovak Chemical Communications. Accepted manuscript [1] Pacheco, J.G.; Valente, I.M.; Gonçalves, L.M.; Magalhães, P.J.; Rodrigues, J.A.; Barros, A.A. Talanta. 2010, 81, 372 [3] Gonçalves, L.M.; Pacheco, J.G.; Magalhães, P.J.; Rodrigues, J.A.; Barros, A.A. Food Additives and Contaminants. 2010, 27, 175 September, 811, 2010. ISEL - Lisbon 34
XII Iberian Meeting of Electrochemistry & XVI Meeting of the Portuguese Electrochemical Society O B 02 activity. Gallic acid interference Maria J.F. Rebelo, Dulce M.A. Gil CCMM -Faculdade de Ciências da Universidade de Lisboa, Campo Grande, C 8 1749-016 Lisboa, Portugal, mjrebelo@fc.ul.pt It is, nowadays, common knowledge that wines contain polyphenols, which make them polyphen which had a good correlation to the antioxidant activity of several Portuguese wines, measured by the ABTS assay, r = 0.9795 (p < 0.05). Folin-Ciocalteu assay, which takes gallic acid as reference, most of the times. So, we studied the influence of gallic acid in enzymatic assays in more detail. The interaction of gallic acid in free (with UV-Vis spectrophotometric detection) and immobilized (with amperometric biosensor detection) Laccase enzyme oxidation of caffeic acid is presented. IC 50, was determined to be 19.15 ± 0.11 µM and 5.11 ± 0.19 µM for free and immobilized enzyme, respectively. The gallic acid study was complemented with cyclic voltammetry of separate and mixed solutions of caffeic and gallic acid, at bare or covered by membranes with immobilized laccase glassy carbon electrodes and will be presented. Aknowledgements: D.M.A Gil acknowledges F CT (Fundação para a Ciência e a Tecnologia) for a Ph.D. fellowship (SFRH/BD/34511/2006). The authors acknowledge Financial support from Faculdade de Ciências da Universidade de Lisboa September, 811, 2010. ISEL - Lisbon 35
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