Soluble semiconducting poly(3-octylthiophene) as a solid-contact material in all-solid-state chloride sensors

All-solid-state chloride sensors based on poly(3-octylthiophene) (POT) as ion-to-electron transducer were studied by electrochemical impedance spectroscopy (EIS) and potentiometric measurements. POT was deposited by solution casting on a glassy carbon (GC) substrate and then coated with a layer of plasticized PVC, containing tridodecylmethylammonium chloride (TDMACl) as the ion-exchanger. Highly reproducible and stable chloride sensors were fabricated with the concentration of TDMACl in the PVC membrane varying in the range of 5–15% (w/w). The presence of TDMACl also in the POT layer was found to significantly decrease the electrode impedance but did not influence the potentiometric response of the chloride sensors studied. Conditioning of the POT layer in AgNO3, prior to casting of the PVC membrane, slightly improved the potential stability of the electrode (due to the presence of silver in POT) but did not lower the detection limit. The response of the GC/POT/PVC–TDMACl electrode was comparable to that of GC/PEDOT/PVC–TDMACl electrode studied earlier. However, the GC/POT/PVC–TDMACl electrodes are easier to prepare, as the electropolymerization step of PEDOT solid-contact can be avoided. The absence of water (layers) between the solid-contact and the PVC–TDMACl membranes was verified by performing the so-called “water-layer test”.