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

XII Iberian Meeting of Electrochemistry & XVI Meeting of the Portuguese Electrochemical Society PB 01
Voltammetric Analysis of Sulphites in Alcoholic Beverages
using Gas-Diffusion Microextraction
Manuel P. C ruz, Inês M. Valente, Luís M. Gonçalves,
João P. Pacheco, José A. Rodrigues, Aquiles A. Barros
Requimte, Departamento de Química e Bioquímica, Faculdade de Ciências da Universidade do
Porto. Rua do Campo Alegre, n.º 687, 4169-007 Porto, Portugal
jarodrig@fc.up.pt
The purpose of this study was to develop a voltammetric methodology aiming sulphite
determination using a hanging mercury drop electrode, based on prior extraction of
sulfur dioxide (SO 2 ) by gas-diffusion microextraction (GDME). Sulphites are widely
used as preservatives in the food industry for their several roles including the prevention
of undesirable microbial growth and oxidation processes [1]. 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 [2].
GDME is an innovative technique that combines the advantages of membrane aided gasdiffusion
with microextraction concepts [3,4]. GDME makes uses of a novel portable
and low-cost device that comprises a small, commercially available, semi-permeable
membrane. Volatile compounds released by the sample can permeate the membrane
pores and are collected by an adequate solution. Some of the advantages of this
extraction system are: the experimental simplicity of the sample preparation process, the
use of a disposable small sized membrane and the possibility of extraction of volatile
compounds at low temperatures. The methodology is based on the sample acidulation
transforming all sulphites into SO 2 that volatilizes and is collected, after passing through
the membrane, by the existing solution within the extraction module. Such solution is
acetate buffer in which there is a reaction of conversion of SO 2 into non volatile HSO 3 - .
After a certain period of time, this solution is collected and analyzed by SWV. The
results were compared with the method of Ripper (Portuguese Norm 2220).
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] Bird, D Understanding wine technology: The science of wine explained, The Wine Appreciation
Guild, 4th ed., EUA, 2005
[2] Almeida, P.J.; Rodrigues, J.A.; Guido, L.F.; Santos, J.R.; Barros, A.A.; Fogg, A.G.
Electroanalysis, 2003, 15, 587
[3] Rodrigues, J.A.; Gonçalves, L.M.; Pacheco, J.G.; Barros, A.A.; PT Patent 104789 (pending),
2009
[4] Gonçalves, L.M.; Magalhães, P.J.; Valente, I.M.; Pacheco, J.G.; Dostálek, P.; Sýkora, D.;
Rodrigues, J.A.; Barros, A.A. Journal Chromatography A, In Press.
September, 811, 2010. ISEL - Lisbon 67