Polypyrrole Films Doped with an Electroactive Sulfonated Chelating Reagent: Electrochemical Characterization and the Detection of Metal Ions

Polypyrrole films doped with the electroactive chelating reagent 3-(2-pyridyl)-5,6-diphenyl-4,4′-disulfonate-1,2,4-triazine (PDTDS2–) were prepared and characterized. The electroactive azo bond in PDTDS2– was detected in the polymer film by cyclic voltammetry. The ratio of pyrrole to PDTDS2– in the films (as evaluated from azo reduction and polymer growth charges) was 11.7:1 (s =2.03, n=38), quite close to the expected ratio of 8:1 for a doubly charged anion-doped film. The azo bond electrochemistry in the polypyrrole exhibited Nernstian pH behavior (ΔEf/Δ pH=–54.7±1.3 mV dec–1). Copper detection by medium-exchange cyclic voltammetry at these films was examined and it was found that both reduction and stripping, oxidation responses were obtained but the latter was better as it was narrower and larger in magnitude. Thinner films gave better copper responses and detection of Cu2+ down to 1×10 –6 mol dm–3 was possible at films prepared with a growth charge of about 40 μC. Selectivity was evaluated in mixture experiments and a range of commonly occurring ions did not interfere in the Cu2+ electrochemical detection. The most severe interferents were mercury(II) and EDTA; new voltammetric peaks for Ag(I) and Hg(II) were observed.