Abstract: The adsorption process of cetyl pyridinium bromide (CPyBr) on glassy carbon (GC)electrode surface in a long optical path length thin-layer cell(LOPLTC) has been investigated by an AC impedance measurement. In the high freqency region of the AC impedance complex diagram, the capacity obtained from a large semicircle with rotation was 4 times larger than that theoretically calculated from a parallel plate condenser. In the low frequency region the impedance diagrams were related to the adsorption of CPyBr and the Warburg′s impedance. A charge transfer model between the layer of CPyBradsorbed on GC electrode surface and the bulk soluticn has been suggested. A low value ofdiffusion coefficient and large fluid dynamics radius of CPyBr (r=352Å) were calculated from Warburg′s impedance. An equivalent circuit for the impedance in the whole frequency tested has been suggested.

Key words: AC impedanoc measurement, Surfactant, Cetyl pyridinium bromide, Surface adsorption, Electrochemiscal analysis