Polypyrrole ion-gate membranes were produced by electrochemical polyme
rization of pyrrole onto a gold-covered quartz crystal from aqueous so
dium tosylate solutions under varying experimental conditions with the
aim of finding the optimum conditions for the use of such a membrane
for the release of anionic drugs. The variables studied were the poten
tial of polymerization, pH, temperature and the relative permittivity
of the solution. The n Values determined for the polymerization reacti
on were about 2.24 and they were found to be quite independent of the
polymerization conditions used. The effect of temperature and the rela
tive permittivity of the solvent on the doping levels and the ion exch
ange properties was of minor importance. The cathodic reduction of the
ion-gate membrane, however, showed that if mainly anions are to be re
leased from the membrane the polymerization potential has to be above
900 mV (on the calomel electrode scale) and the pH of the electrolyte
solution should be neutral or acidic. If this potential is kept below
800 mV and the pH of the solution in which reduction of the membrane i
s performed is alkaline, cations should be the main species moving. Im
pedance measurements and a separate determination of the apparent acti
vation energy (6.8 kJ mol(-1)) confirmed that, in the oxidized state o
f the membrane, ion transport within the film is the main rate-limitin
g process. (C) 1998 Elsevier Science S.A.