POTENTIOMETRIC ANION RESPONSE OF POLY(TETRAKIS(P-AMINOPHENYL)PORPHYRIN) FILM-MODIFIED ELECTRODES

The potentiometric response to anions of glassy carbon electrodes coated with thin unmetallated poly(tetrakis(p-aminophenyl)porphyrin) (poly(H2(p-TAPP))) films is examined. The polymer films are introduced onto the glassy carbon surface by constant-potential anodic electrolysis of the porphyrin monomer from a solution of dichloromethane containing a quaternary ammonium perchlorate salt. The thickness of the film is controlled by the electrodeposition time. Oxidized poly(porphyrin) modified electrodes exhibit near Nernstian response to iodide in the concentration range of 5 x 10(-5) - 1 x 10(-1) M with significant selectivity over a wide range of other anions tested. The mechanism of the electrode's iodide ion response is considered in light of its response to other redox-active anions, and a recent literature report describing the selective iodide response of electrodes coated with electropolymerized poly(3-methylthiophene) films. Spectroelectrochemical studies with poly(porphyrin)-modified tin oxide electrodes are used to confirm the redox-type response mechanism of the sensors toward iodide. The analytical limitations of using such polymer film-modified electrodes for potentiometric ion sensing are discussed.