Sensitivity and Selectivity of Polypyrrole Based AC-Amperometric Sensors for Electroinactive Ions – Frequency and Applied Potential Influence
Abstract
Oxidation/reduction of polypyrrole films coupled with ion exchange on the polymer/solution interface can be utilized for amperometric sensing of electroinactive ions. Anion or cation exchanging films (polypyrrole doped by chloride or poly(4-styrenesulfonate) ions, respectively) can be used to determine common anions (as Cl−, NO, SO etc) or cations (K+, Na+, Li+, Ca2+, Mg2+) under conditions of alternating current (AC) amperometry in the range 10−4–1 M. A sensitivity can be tuned by choosing appropriate electrode potential, corresponding to polypyrrole oxidation (anion-exchanging films) or reduction (cation-exchangers). Electrochemical impedance spectroscopy and AC-voltammetry studies have shown that applied frequency and potential could also affect the observed dependence of the signal (admittance or AC-current) on ion concentration. For high frequency the sensitivity is higher but selectivity lower, due to influence of solution conductivity on the response. For low frequencies the sensitivity is lower; however, a selectivity increase was observed due to diverse mobility of ions in the polymer film. Selectivity of AC-amperometric responses was studied both in separate and mixed solutions.