Electrochemistry of conductive polymer X: Polyaniline‐based potentiometric sensor for dissolved oxygen

Abstract

A platinum electrode coated with plyaniline (PA) was examined as a potentiometric or an optical .sensor for dissolved oxygen, and the results are reported. While the polymer-modified electrode behaved satisfactorily a s a potentiometric sensor, i Ls optical response (i.e., absorbance) gave a narrow linear region for varied oxygen concentrations. This conducting polymer-coated electrode was characterized to give approximately 97 mV/decade of the oxygen concentration and a voltage signal range of about 400 mV, representing at least three orders of magnitudes of dynamic linearity over the dissolved oxygen concentration. The potentiometric sensing electrode showed reasonably short response times, excellent reproducibility, and good stability. A detection limit of about 5 X lo-' mol/L of dissolved oxygen was estimated from the potentiometric response of PA-coated electrodes. ZNTRODUCTIONOxygen sensors have received a great deal of interest due to their importance in analyzing oxygen in industrial, environmental, and medical applications [ 1-41. Oxygen sensors can be classified broadly into three categories:( 1 ) a solid-state type operating normally at high temperatures [ 11, which includes solid electrolytes such as calciadoped zirconia and semiconductors such as titania or other metal oxides; ( 2 ) fluoroescence or phosphorescence sensors [2], which utilize the ability of oxygen to quench fluorescence or phosphorescence of polycyclic aromatic hydrocarbons such a s 9,lO-diphenylanthracene or pyrene derivatives; and ( 3 ) electrochemical sensors [3,4], which usually measure the faradaic current for oxygen reduction. The first two categories of sensors are suitable for quantitating oxygen in a gas mixture at various temperatures, while the electrochemical sensor is generally used for the dissolved oxygen analysis.The importance of analysis of dissolved oxygen in various liquids is well summarized by Hitchman To whom correspondence should be addressed. electrode (MPOE) [ 4 ], requires that both the ca'thode and anode be sealed by a membrane through which oxygen permeates and is reduced at the cathode. Thus, selection of materials for a membrane as well a s a working electrode constitutes a major problem for the Clark cell. Due to the irreversible nature of the oxygen reduction at almost any electrode, properly chosing the electrode material is very important. Gold is regarded a s the best electrode material because of its low adsorption of oxygen and of the high overpotential for the formation of its oxide [4]. The loss of electrolyte through the membrane is another problem. Kecently, silver has also been used as a cathode along with an Ag/AgCI anode/reference electrode [ 5 ] . Polyaniline (PA) has been studied extensively as one of conducting polymers due primarily to its straightforward preparation methods and the stabihy of its doped state under ambient experimental conditions [6-231. During the course of these studies, we [24-291 discovered that PA has four different oxidation states depending on the potenti...

Potentiometric Ion Sensors Based on Conducting Polymers

“…In addition to redox potential measurements [168], the redox response of a conducting polymer may be utilized for potentiometric sensing of the respective monomer [170] or other neutral species like oxygen [171,172]. The redox response plays a role also in the signal generation of the PPybased amperometric ammonia sensor [173 ± 175].…”

Transdutores potenciométricos a base de polímeros condutores: aplicações analíticas

“…Um sensor potenciométrico para O 2 dissolvido baseado em polianilina, PANI, é descrito por Shim et al 41 . Filmes de PANI foram depositados por voltametria cíclica sobre eletrodos de platina, sendo caracterizados por apresentarem cerca de 97 mV/ década, vs. Ag/AgCl saturado com KCl, em concentração de O 2 , e sinal potenciométrico na faixa de 400 mV, representando no mínimo 3 ordens de magnitude para faixa linear de O 2 dissolvido.…”

“…Respostas ópticas para o sensor foram também estudadas, porém apresentando menor região linear para detecção de O 2 dissolvido, cerca de 50% da concentração obtida. O método utiliza medidas no aumento da banda de absorção a 800 nm, pela oxidação do PANI, sendo diretamente proporcional à concentração de O 2 inicial presente na solução 41 . Bobacka et al 44 mostram um novo conceito de eletrodos íon-seletivos (EIS) de membrana sólida, onde polímeros condutores, polioctiltiofeno (POT) e polianilina (PANI), são incorporados juntamente com membranas matrizes de cloreto de polivinila (PVC) e ionóforos para Li + e Ca 2+ , respectivamente.…”

“…Idealmente, a dependência da concentração com o potencial é obtida pela equação de Nernst: E = E' + RT/nF ln (a PANIox /a PANIred ) onde a PANIox e a PANIred são as respectivas atividades do polímero nos estados oxidado e reduzido dentro do filme, gerados pela reação com O 2 . O valor de n=0,5/unidade de PANI, foi calculado por métodos espectroscópicos e coulométricos; a reação provável que ocorre na interface polímero-solução (omitindo a dependência de protonação da anilina pela variação de pH) é dada por 41 :…”

The Scientific Legacy of Su-Moon Park: a Personal View

“…These papers are among the most highly cited of Park's impressive list of publications. [42][43][44][45][46][47] The general theme of imbuing organic polymers with interesting, useful properties such as electronic conductivity was then just at the very beginning, but it continues even today. Polyaniline, for example, has turned out to be an exceedingly versatile material, finding applications in electroanalysis, batteries and fuel cells.…”