Electrochemical behavior and analytical utility of a controlled porosity cellulose acetate film bearing 2,6-dichlorophenolindophenol

Glassy carbon electrodes coated with a cellulose acetate film incorporating 2,6-dichlorophenoiindophenol (CA/DCPI) were developed. At this multifuncti onal coating DCPI serves as a mediator for the electron transfer kinetics a nd in conjunction with the cellulose acetate's size exclusion properties it results in a chemical sensor with great selectivity and stability. Access to the surface can be manipulated via controlled hydrolysis of the film in KOH or ZnCl2 solutions. Different permeabilities are obtainable by hydrolyz ing the him over different time periods. Diffusion coefficients D-app of th ese films for analytes of different molecular sizes were determined with do uble step chronocoulometry. The electrochemical characteristics of the immo bilized DCPI were explored using cyclic voltammetry. The formal potentials of the immobilized DCPI coating hydrolyzed in KOH, ZnCl2 and with ZnCl2 in the casting solution were found to be 70, 75, and 79 mV (vs. Ag/AgCl/ 3M KC l), respectively, at pH 6.5. The dissociation constants of the DCPI redox c ouple were found to be 5.2 +/- 0.1 (pKr) and 7.4 +/- 0.05 (pKo). The electr ochemical rate constant k(o) of the of DCPI redox couple within the film wa s also evaluated. The behavior of the sensor towards different reducing com pounds was investigated. The sensors showed good operational and storage st ability.