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 PB 06 Thiol monolayers on bismuth electrodes for organic matter fouling prevention in the voltammetric stripping analysis of heavy metals María de la Gala Morales, Eduardo Pinilla Gil, Lorenzo Calvo Blázquez Department of Analytical Chemistry, University of Extremadura, Av. de Elvas, s/n 06006 Badajoz, Spain mgalamor@gmail.com Stripping voltammetric measurements of heavy metals are frequently hampered by electrode fouling due to adsorption of organic compound naturally occurring in a variety of real samples (e.g. ambient and residual waters or biological fluids). A strategy to manage this problem is electrode protection by an isolating layer permeable to the small ionic analytes but not to the much larger interfering organic compounds. Disorganized monolayers of thiols with short alkyl chains and bulky end group have been proven useful for gold electrode protection against model surfactants [1] and humic acid [2]. Thiol monolayers deposition on bismuth electrodes, a widely used environmentally friendly alternative to mercury electrodes, has been studied and their general electrochemical behaviour described [3], but no data is available about the applicability of thiol protected bismuth electrodes for the determination of heavy metals in presence of organic surfactants. In this work, we have explored the voltammetric stripping behaviour of Zn(II), Cd(II) and Pb(II) on a homemade bismuth disk electrode before and after deposition of a disorganized monolayer of different thiols, using Triton X-100 as a model organic interfering compound. Chemical and instrumental parameters were explored for obtaining the optimal metal ions response in the µg/L range. We found that mercaptoacetic acid effectively protects the electrode against fouling by relatively high Triton X-100 concentration, in the range 100 to 200 mg/L without significantly affecting the Pb(II) response, which is almost completely suppressed when the bare bismuth electrode is exposed to the surfactant. These preliminary results are promising for the possible application of voltammetric sensors based on bismuth working electrode surfaces for the direct determination of heavy metals in untreated real samples. Acknowledgments: This work is supported by the Spanish Ministry of Science and Innovation (project CTQ2008-06657/BQU). References [1] Herzog, G; Arrigan, D.W. Anal. Chem., 2003, 75, 319 [2] Herzog, G; Beni, V.; Dillon, P.H.; Barry, T.; Arrigan, D.W. Anal. Chim. Acta, 2004, 511, 137 [3] Adamovski, M.; Zajac, A.; Gründler, P.; Flechsig, G.U. Electrochem. Commun., 2006, 8, 932 September, 811, 2010. ISEL - Lisbon 72
XII Iberian Meeting of Electrochemistry & XVI Meeting of the Portuguese Electrochemical Society PB 07 Electrochemiluminescence of luminol/H 2 O 2 system catalyzed by ferrocenes derivatives in solution on I T O electrode Diogo Ramadas 1,2 , Ana S. Viana 2 , A.C. Cascalheira 1 1 Lumisense,Lda, Edifício ICAT, Campo Grande, 1749-016 Lisboa, Portugal 2 CQB, Departamento de Química e Bioquímica, Faculdade de Ciências da Universidade de Lisboa, Campo Grande, 1749-016 Lisboa, Portugal drsousa@fc.ul.pt Luminol is one of the earliest known synthetic compounds exhibiting chemiluminescence and has been extensively studied regarding its analytical applications. The employment of electrochemiluminescence (ECL) of luminol systems onto analytical determinations suffers from a continuous decrease of the light signal during consecutive electrode perturbation, which results on poor reproducibility [1]. The decrease in the signal has been attributed to the electrode fouling/passivation due to deposition of poisoning compounds, products of the ECL reaction. The use of ferrocene derivatives as catalysts in the ECL of luminol/H 2 O 2 system was investigated on several authors in various electrode materials [2-4]. Most of those studies concern the use of ferrocene derivatives as labels for biomolecules and optical ECL detection. However, since these derivatives can also function as mediators for the ECL reaction it can be envisaged that they can prevent the electrode fouling and consecutively increase the stability of ECL systems based on the luminol reaction. In this study, we compare the ECL response of an alkaline solution of luminol and H 2 O 2 in the presence of three different ferrocene derivatives (ferrocene monocarboxylic acid, ferrocene dicarboxylic acid, ferrocene carboxaldehyde) onto a ITO electrode, by linear voltammetry or potential pulse application. The obtained results indicate that ferrocene monocarboxylic acid is the most promising derivative, since it catalyzes the reaction by 120 mV; the light emission of the system without ferrocene starts at 360mV (vs. SCE) whereas in the presence this mediator can be detected at 240mV (vs. SCE). The recorded currents corroborate the optical results revealing that the onset of the optical signal corresponds to the beginning of the oxidation of the ferrocene derivatives. A systematic studied has been also performed in order to study the influence of the: ratio concentration of Ferrocene/Luminol, pH, and buffer nature on the reproducibility and intensity of the optical signal. Acknowledgments: Diogo Ramadas acknowledge Fundação para Ciência e Tecnologia, for financial support, project SFRH / BDE / 33797 / 2009 References [1] C. A. Marquettc and L.J. Blum. Anal. Chim. Acta , 1999, 381, p. 1 [2] R. Wilson and D. Schiffrin. J. Electroanal. Chem., 1998, 448, p. 125 [3] R. Wilson and D. Schiffrin. Anal. Chem., 1996, 68, p. 1254 [4] C. E. Taylor, Stephen E. Creager, J.Electroanal.Chem., 2000, 485, p. 114 September, 811, 2010. ISEL - Lisbon 73
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