Electrochemical recognition of metal cations by poly(crown ether ferrocene) films investigated by cyclic voltammetry and electrochemical impedance spectroscopy

The electrochemical behavior of the pyrrole-substituted crown ether ferroce ne 1 was investigated in detail in 0.1 A I TBAP + CH3CN by cyclic voltammet ry (CV) and chronoamperometry. In the potential range 0-0.7 V, a reversible diffusion-controlled process was observed with a formal potential of 0.53 V corresponding to the ferrocene/ferricinium redox couple. Electro-oxidativ e polymerization of 1 was accomplished either by repeated CV scans, or by c ontrolled potential electrolysis. The resulting polymer films were tested i n acetonitrile electrolyte for the amperometric recognition of alkali and a lkaline earth metal cations. Their remarkable recognition properties toward s Ca2+ and Ba2+ cations have been confirmed by electrochemical impedance sp ectroscopy (FIS). EIS allowed construction of a calibration curve based on the variation of the low frequency capacity of the film as a function of th e guest cation concentration, reflecting the variation of the formal potent ial between the free and the complexed immobilized redox couple. Capacity m easurements using EIS appear to be an attractive method for cation sensing with films based on molecular redox receptors. (C) 1999 Elsevier Science S. A. All rights reserved.