R. Demarco et al., ELECTROCHEMICAL IMPEDANCE SPECTROSCOPY STUDY OF THE RESPONSE MECHANISM OF THE JALPAITE CU-II ION-SELECTIVE ELECTRODE IN SEAWATER, Analytical chemistry (Washington), 70(22), 1998, pp. 4683-4689
This paper presents the results of a novel study into the response mec
hanism of the jalpaite copper(II) ion-selective electrode(ISE) using e
lectrochemical impedance spectroscopy (EIS) under conditions of minima
l overpotential stimulation (i.e., +/-10 mV). The EIS spectra of the j
alpaite ISE in seawater and other ionic media revealed a high-frequenc
y surface film impedance that is attributable to the modified hydrated
surface layers of the ISE, and a low-frequency charge-transfer impeda
nce that can be ascribed to the reductive ion-exchange of Cu-II at the
membrane/electrolyte interface. EIS data for a rotating disk electrod
e have shown that the charge-transfer process is under diffusion contr
ol. MS and potentiometric response data in UV-oxidized seawater spiked
with humic acid imply that organic complexation of Cu-I at the electr
ode diffusion layer is responsible for a weak interference effect. The
classical chloride interference effect of the jalpaite Cu-II ISE occu
rring at high concentrations of Cu-II (i.e., > 10(-6) M) yields an MS
response similar to the one observed with organic ligands. An EIS expe
riment for a jalpaite Cu-II ISE aged in seawater for 72 h demonstrated
that the charge-transfer impedance is constant until electrode releas
e of Cu-II exceeds the complexing capacity of seawater, and this mecha
nistic information is consistent with the hypothesis that electrode di
ssolution can be used to autotitrate the natural ligands in seawater.