Self-assembled monolayers (SAMs) of crown ether adsorbates on gold reversib
ly bind metal ions from aqueous solutions. The resulting changes of the ele
ctrochemical properties of the monolayers were monitored by impedance spect
roscopy. The increased dielectric constant of the layer due to the complexa
tion of ions results in an increase of the monolayer capacitance (C-ML). An
alysis of the response curves with a Langmuir isotherm enables the determin
ation of association constants of the SAMs with various metal ions. The cat
ion binding also influences the charge-transfer resistance (R-CT) Of a redo
x couple Ru(NH3)(6)(2+/3+) in the electrolyte. Comparison of both responses
allows an accurate interpretation of the origin of the resistive response.
Furthermore, the association constants enable the quantitative determinati
on of interactions between SAMs and metal ions, using either capacitive or
resistive responses.