A chem. modified platinum electrode with coated poly[tetra(4-animophenyl)porphyrin] (PTAPP) was to be used as a new potentiometric iodide selective electrode. The mechanism of the electrode potential response is based on strong host-guest effect between protonized three-dimensional cross linked polycyclic PTAPP film and I- ion. The resulting electrode demonstrates a selectivity sequence different from this conventional Hofmeister series and the behavior of ordinary metal porphyrin complexes: I- ?SCN- ?ClO4- > Br- > NO2- > NO3- > Cl- > SO42-. The response of the electrode is linear in the 10-1 to 2.6 ?10-6 mol dm-3 I- with a detection limit of 8.2 ?10-7 mol dom-3 and a slope 61 ?0.2 mV/pI-(n = 5, 27癈). The PTAPP electrode has the advantages of simplicity, low resistance, fast response, fair stability and reproducibility, and resistance to poison. The a.c. impedance spectra of the polymer membrane have also been studied.

Key words: PORPHINE P, PLATINUM, ION SELECTIVE ELECTRODE, MEMBRANE ELECTRODES, IODIDE ION, ELECTROCHEMICAL REACTION, CHEMICAL MODIFIED ELECTRODE