CAPACITIVE DETECTION OF SURFACTANT ADSORPTION ON HYDROPHOBIZED GOLD ELECTRODES

Nonspecific adsorption of surfactants on polycrystalline gold electrod es, covered by a chemically adsorbed monomolecular layer of octadecane thiol, was studied by means of capacitive measurements. Homologous ser ies of fatty acids (from decane to tetradecane acids) and dodecanepyri dinium chloride were used as surfactants. The behavior of the electrod e was completely different in the first and subsequent cycles of adsor ption/desorption. In the first adsorption cycle, an initial capacitanc e jump at low concentrations (<10 mu M) occurs, while later the curves show the usual saturation behavior. The first surfactant layer could not be completely desorbed; only the electrode capacitance shown after the jump was reached. Subsequent cycles do not reveal any capacitance jumps and were completely reversible. Adsorption curves in the series of monoalkyl acids are shifted according to the Traube rule. A compar ison with the surfactant adsorption at the air/water interface has bee n done.