Abstract: The impedance of SnO₂ electrode modified by ferrocene derivative——ferrocenyl-n-octadecanoale L-B films was measured. The estimation of element parameter values occurring in equivalent circuit was performed by using simplex method. Reaction rate constant K_s was also determined. Analysis of interface impedance and electrode reaction kenitic performances indicated that modified ferrocenyl-n-octadec-anoale L-B films show impedance behaviours of electroactive molecules differing obviously with that obtained in solid state. The fact that ferrocenyl-n-octadecanoale L-B films act as charge transfer mediator in SnO₂/Fe(CN)₆^3-/4- redox reaction was proved.

Key words: modified electrode, interface impedance, equivalent circuit, charge transfer, L-B films