Electroactivity of poly(3-methyl-thiophene) in aqueous solutions of inorganic salts

Poly-(3-methyl-thiophene) (P3MeT) shows unusual strong sensitivity towards certain ions in aqueous solutions, unknown in organic solvents. Voltammograms of P3MeT in 0.1 M KNO₃(aq) exhibits a strong virginal anodic peak near 900 mV (Ag/AgCl), while the corresponding cathodic "peak" is smeared out over several hundred mV. The anodic current response of P3MeT is strong in NO₃(aq) and in ClO₄aq) solutions, and weak in Cl(aq) and SO₄^2- (aq) solutions, which may indicate a correlation with the oxidation power of the anions employed. The strong response towards nitrate ions suggests the use of P3MeT as a sensor material.