Conducting Polymers as Sensor Materials for the Electrochemical Detection of Pesticides
An interaction study between the pesticides methylparathion, paraquat, bentazon, glyphosate and the conducting polymers (polyaniline and polypyrrole) was carried out using optical and electrochemical methods, in order to evaluate their use in modified polymer–carbon paste electrodes for the electrochemical detection of these pesticides. The UV-visible spectrophotometric analysis was applied to investigate the doping characteristics of these conducting polymers and the sorption processes of these pesticides on these polymers. Kinetic sorption studies showed that the pesticides presented variable sorption behavior on each of the polymer studied. Cyclic voltammetric analysis of these pesticides with two types of modified carbon paste electrodes (CPE1: mixed graphite paste+5% polymer; CPE2: direct polymerization of the polymer on graphite powder) was performed in phosphate buffer. Results obtained with the CPE2-polyaniline electrode showed a linear increase of the cathodic and anodic currents with the pesticide concentration in potentials around 200 mV and 0 mV, for the bentazon, glyphosate and 2,4-D, whereas no response was observed for paraquat and methylparathion. The electrochemical response on the modified carbon paste-polypyrrole electrode was more intense for the CPE1 electrode. Based on the sorption studies using UV-visible spectrophotometry and on the voltammetric analysis with the modified carbon paste/polymer electrodes it can be shown that the pesticides with acidic characteristics (2,4-D, gliphosate and bentazon) are readily sorbed on the dedoped polymer, increasing the voltammetric response of the CPE2 electrode. However, low interaction was observed between these acidic pesticides and the polypyrrole, suggesting that electrostatic interaction are dominant in the sorption of such pesticides without doping of the polypyrrole by protonation, since the paraquat is an ionic pesticide.
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Document Type: Research Article
Publication date: September 1, 2006
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